what is review related literature and studies

Review of Related Literature: What Is RRL & How to Write It + Examples

A review of related literature is a separate paper or a part of an article that collects and synthesizes discussion on a topic. Its purpose is to show the current state of research on the issue and highlight gaps in existing knowledge. A literature review can be included in a research paper or scholarly article, typically following the introduction and before the research methods section.

This article will clarify the definition, significance, and structure of a review of related literature. You’ll also learn how to organize your literature review and discover ideas for an RRL in different subjects.

🔤 What Is RRL?

• ❗ Significance of Literature Review
• 🔎 How to Search for Literature
• 🧩 Literature Review Structure
• ✍️ How to Write an RRL
• 📚 Examples of RRL

🔗 References

A review of related literature (RRL) is a part of the research report that examines significant studies, theories, and concepts published in scholarly sources on a particular topic. An RRL includes 3 main components:

• A short overview and critique of the previous research.
• Similarities and differences between past studies and the current one.
• An explanation of the theoretical frameworks underpinning the research.

❗ Significance of Review of Related Literature

Although the goal of a review of related literature differs depending on the discipline and its intended use, its significance cannot be overstated. Here are some examples of how a review might be beneficial:

• It helps determine knowledge gaps .
• It saves from duplicating research that has already been conducted.
• It provides an overview of various research areas within the discipline.
• It demonstrates the researcher’s familiarity with the topic.

🔎 How to Perform a Literature Search

Including a description of your search strategy in the literature review section can significantly increase your grade. You can search sources with the following steps:

🧩 Literature Review Structure Example

The majority of literature reviews follow a standard introduction-body-conclusion structure. Let’s look at the RRL structure in detail.

Introduction of Review of Related Literature: Sample

An introduction should clarify the study topic and the depth of the information to be delivered. It should also explain the types of sources used. If your lit. review is part of a larger research proposal or project, you can combine its introductory paragraph with the introduction of your paper.

Here is a sample introduction to an RRL about cyberbullying:

Bullying has troubled people since the beginning of time. However, with modern technological advancements, especially social media, bullying has evolved into cyberbullying. As a result, nowadays, teenagers and adults cannot flee their bullies, which makes them feel lonely and helpless. This literature review will examine recent studies on cyberbullying.

Sample Review of Related Literature Thesis

A thesis statement should include the central idea of your literature review and the primary supporting elements you discovered in the literature. Thesis statements are typically put at the end of the introductory paragraph.

Look at a sample thesis of a review of related literature:

This literature review shows that scholars have recently covered the issues of bullies’ motivation, the impact of bullying on victims and aggressors, common cyberbullying techniques, and victims’ coping strategies. However, there is still no agreement on the best practices to address cyberbullying.

Literature Review Body Paragraph Example

The main body of a literature review should provide an overview of the existing research on the issue. Body paragraphs should not just summarize each source but analyze them. You can organize your paragraphs with these 3 elements:

• Claim . Start with a topic sentence linked to your literature review purpose.
• Evidence . Cite relevant information from your chosen sources.
• Discussion . Explain how the cited data supports your claim.

Here’s a literature review body paragraph example:

Scholars have examined the link between the aggressor and the victim. Beran et al. (2007) state that students bullied online often become cyberbullies themselves. Faucher et al. (2014) confirm this with their findings: they discovered that male and female students began engaging in cyberbullying after being subject to bullying. Hence, one can conclude that being a victim of bullying increases one’s likelihood of becoming a cyberbully.

Review of Related Literature: Conclusion

A conclusion presents a general consensus on the topic. Depending on your literature review purpose, it might include the following:

• Introduction to further research . If you write a literature review as part of a larger research project, you can present your research question in your conclusion .
• Overview of theories . You can summarize critical theories and concepts to help your reader understand the topic better.
• Discussion of the gap . If you identified a research gap in the reviewed literature, your conclusion could explain why that gap is significant.

Check out a conclusion example that discusses a research gap:

There is extensive research into bullies’ motivation, the consequences of bullying for victims and aggressors, strategies for bullying, and coping with it. Yet, scholars still have not reached a consensus on what to consider the best practices to combat cyberbullying. This question is of great importance because of the significant adverse effects of cyberbullying on victims and bullies.

✍️ How to Write Review of Related Literature – Sample

Literature reviews can be organized in many ways depending on what you want to achieve with them. In this section, we will look at 3 examples of how you can write your RRL.

Thematic Literature Review

A thematic literature review is arranged around central themes or issues discussed in the sources. If you have identified some recurring themes in the literature, you can divide your RRL into sections that address various aspects of the topic. For example, if you examine studies on e-learning, you can distinguish such themes as the cost-effectiveness of online learning, the technologies used, and its effectiveness compared to traditional education.

Chronological Literature Review

A chronological literature review is a way to track the development of the topic over time. If you use this method, avoid merely listing and summarizing sources in chronological order. Instead, try to analyze the trends, turning moments, and critical debates that have shaped the field’s path. Also, you can give your interpretation of how and why specific advances occurred.

Methodological Literature Review

A methodological literature review differs from the preceding ones in that it usually doesn’t focus on the sources’ content. Instead, it is concerned with the research methods . So, if your references come from several disciplines or fields employing various research techniques, you can compare the findings and conclusions of different methodologies, for instance:

• empirical vs. theoretical studies;
• qualitative vs. quantitative research.

📚 Examples of Review of Related Literature and Studies

Have you ever struggled with finding the topic for an RRL in different subjects? Read the following paragraphs to get some ideas!

Nursing Literature Review Example

Many topics in the nursing field require research. For example, you can write a review of literature related to dengue fever . Give a general overview of dengue virus infections, including its clinical symptoms, diagnosis, prevention, and therapy.

Another good idea is to review related literature and studies about teenage pregnancy . This review can describe the effectiveness of specific programs for adolescent mothers and their children and summarize recommendations for preventing early pregnancy.

📝 Check out some more valuable examples below:

• Hospital Readmissions: Literature Review .
• Literature Review: Lower Sepsis Mortality Rates .
• Breast Cancer: Literature Review .
• Sexually Transmitted Diseases: Literature Review .
• PICO for Pressure Ulcers: Literature Review .
• COVID-19 Spread Prevention: Literature Review .
• Chronic Obstructive Pulmonary Disease: Literature Review .
• Hypertension Treatment Adherence: Literature Review .
• Neonatal Sepsis Prevention: Literature Review .
• Healthcare-Associated Infections: Literature Review .
• Understaffing in Nursing: Literature Review .

Psychology Literature Review Example

If you look for an RRL topic in psychology , you can write a review of related literature about stress . Summarize scientific evidence about stress stages, side effects, types, or reduction strategies. Or you can write a review of related literature about computer game addiction . In this case, you may concentrate on the neural mechanisms underlying the internet gaming disorder, compare it to other addictions, or evaluate treatment strategies.

A review of related literature about cyberbullying is another interesting option. You can highlight the impact of cyberbullying on undergraduate students’ academic, social, and emotional development.

📝 Look at the examples that we have prepared for you to come up with some more ideas:

• Mindfulness in Counseling: A Literature Review .
• Team-Building Across Cultures: Literature Review .
• Anxiety and Decision Making: Literature Review .
• Literature Review on Depression .
• Literature Review on Narcissism .
• Effects of Depression Among Adolescents .
• Causes and Effects of Anxiety in Children .

Literature Review — Sociology Example

Sociological research poses critical questions about social structures and phenomena. For example, you can write a review of related literature about child labor , exploring cultural beliefs and social norms that normalize the exploitation of children. Or you can create a review of related literature about social media . It can investigate the impact of social media on relationships between adolescents or the role of social networks on immigrants’ acculturation .

📝 You can find some more ideas below!

• Single Mothers’ Experiences of Relationships with Their Adolescent Sons .
• Teachers and Students’ Gender-Based Interactions .
• Gender Identity: Biological Perspective and Social Cognitive Theory .
• Gender: Culturally-Prescribed Role or Biological Sex .
• The Influence of Opioid Misuse on Academic Achievement of Veteran Students .
• The Importance of Ethics in Research .
• The Role of Family and Social Network Support in Mental Health .

Education Literature Review Example

For your education studies , you can write a review of related literature about academic performance to determine factors that affect student achievement and highlight research gaps. One more idea is to create a review of related literature on study habits , considering their role in the student’s life and academic outcomes.

You can also evaluate a computerized grading system in a review of related literature to single out its advantages and barriers to implementation. Or you can complete a review of related literature on instructional materials to identify their most common types and effects on student achievement.

📝 Find some inspiration in the examples below:

• Literature Review on Online Learning Challenges From COVID-19 .
• Education, Leadership, and Management: Literature Review .
• Literature Review: Standardized Testing Bias .
• Bullying of Disabled Children in School .
• Interventions and Letter & Sound Recognition: A Literature Review .
• Social-Emotional Skills Program for Preschoolers .
• Effectiveness of Educational Leadership Management Skills .

Business Research Literature Review

If you’re a business student, you can focus on customer satisfaction in your review of related literature. Discuss specific customer satisfaction features and how it is affected by service quality and prices. You can also create a theoretical literature review about consumer buying behavior to evaluate theories that have significantly contributed to understanding how consumers make purchasing decisions.

📝 Look at the examples to get more exciting ideas:

• Leadership and Communication: Literature Review .
• Human Resource Development: Literature Review .
• Project Management. Literature Review .
• Strategic HRM: A Literature Review .
• Customer Relationship Management: Literature Review .
• Literature Review on International Financial Reporting Standards .
• Cultures of Management: Literature Review .

To conclude, a review of related literature is a significant genre of scholarly works that can be applied in various disciplines and for multiple goals. The sources examined in an RRL provide theoretical frameworks for future studies and help create original research questions and hypotheses.

When you finish your outstanding literature review, don’t forget to check whether it sounds logical and coherent. Our text-to-speech tool can help you with that!

• Literature Reviews | University of North Carolina at Chapel Hill
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• Learn How to Write a Review of Literature | University of Wisconsin-Madison
• The Literature Review: A Few Tips on Conducting It | University of Toronto
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• Methods for Literature Reviews | National Library of Medicine
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Literature Review Research

Literature review, types of literature reviews.

• Finding information
• Additional Resources
• Explains the background of research on a topic
• Demonstrates why a topic is significant to a subject area
• Helps focus your own research questions or problems
• Discovers relationships between research studies/ideas
• Suggests unexplored ideas or populations
• Identifies major themes, concepts, and researchers on a topic
• Tests assumptions; may help counter preconceived ideas and remove unconscious bias.
• Identifies critical gaps, points of disagreement, or potentially flawed methodology or theoretical approaches

Argumentative Review This form examines literature selectively in order to support or refute an argument, deeply imbedded assumption, or philosophical problem already established in the literature. 

Integrative Review Considered a form of research that reviews, critiques, and synthesizes representative literature on a topic in an integrated way such that new frameworks and perspectives on the topic are generated. The body of literature includes all studies that address related or identical hypotheses. A well-done integrative review meets the same standards as primary research in regard to clarity, rigor, and replication.

Historical Review Historical reviews are focused on examining research throughout a period of time, often starting with the first time an issue, concept, theory, phenomena emerged in the literature, then tracing its evolution within the scholarship of a discipline. The purpose is to place research in a historical context to show familiarity with state-of-the-art developments and to identify the likely directions for future research.

Methodological Review This approach provides a framework of understanding at different levels (i.e. those of theory, substantive fields, research approaches and data collection and analysis techniques), enables researchers to draw on a wide variety of knowledge ranging from the conceptual level to practical documents for use in fieldwork.

Systematic Review Uses pre-specified and standardized methods to identify and critically appraise relevant research, and to collect, report, and analyze data from the studies that are included in the review. Typically it focuses on a very specific empirical question.

Theoretical Review

Examines the theory that has accumulated in regard to an issue, concept, theory, phenomena. Helps to establish what theories already exist, the relationships between them, to what degree the existing theories have been investigated, and to develop new hypotheses to be tested. Often this form is used to help establish a lack of appropriate theories or reveal that current theories are inadequate for explaining new or emerging research problems.

* Kennedy, Mary M. "Defining a Literature."  Educational Researcher  36 (April 2007): 139-147.

All content in this section is from The Literature Review created by Dr. Robert Larabee USC

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What are Literature Reviews?

So, what is a literature review? "A literature review is an account of what has been published on a topic by accredited scholars and researchers. In writing the literature review, your purpose is to convey to your reader what knowledge and ideas have been established on a topic, and what their strengths and weaknesses are. As a piece of writing, the literature review must be defined by a guiding concept (e.g., your research objective, the problem or issue you are discussing, or your argumentative thesis). It is not just a descriptive list of the material available, or a set of summaries." Taylor, D.  The literature review: A few tips on conducting it . University of Toronto Health Sciences Writing Centre.

Goals of Literature Reviews

What are the goals of creating a Literature Review?  A literature could be written to accomplish different aims:

• To develop a theory or evaluate an existing theory
• To summarize the historical or existing state of a research topic
• Identify a problem in a field of research 

Baumeister, R. F., & Leary, M. R. (1997). Writing narrative literature reviews .  Review of General Psychology , 1 (3), 311-320.

What kinds of sources require a Literature Review?

• A research paper assigned in a course
• A thesis or dissertation
• A grant proposal
• An article intended for publication in a journal

All these instances require you to collect what has been written about your research topic so that you can demonstrate how your own research sheds new light on the topic.

Types of Literature Reviews

What kinds of literature reviews are written?

Narrative review: The purpose of this type of review is to describe the current state of the research on a specific topic/research and to offer a critical analysis of the literature reviewed. Studies are grouped by research/theoretical categories, and themes and trends, strengths and weakness, and gaps are identified. The review ends with a conclusion section which summarizes the findings regarding the state of the research of the specific study, the gaps identify and if applicable, explains how the author's research will address gaps identify in the review and expand the knowledge on the topic reviewed.

• Example : Predictors and Outcomes of U.S. Quality Maternity Leave: A Review and Conceptual Framework:  10.1177/08948453211037398  

Systematic review : "The authors of a systematic review use a specific procedure to search the research literature, select the studies to include in their review, and critically evaluate the studies they find." (p. 139). Nelson, L. K. (2013). Research in Communication Sciences and Disorders . Plural Publishing.

• Example : The effect of leave policies on increasing fertility: a systematic review:  10.1057/s41599-022-01270-w

Meta-analysis : "Meta-analysis is a method of reviewing research findings in a quantitative fashion by transforming the data from individual studies into what is called an effect size and then pooling and analyzing this information. The basic goal in meta-analysis is to explain why different outcomes have occurred in different studies." (p. 197). Roberts, M. C., & Ilardi, S. S. (2003). Handbook of Research Methods in Clinical Psychology . Blackwell Publishing.

• Example : Employment Instability and Fertility in Europe: A Meta-Analysis:  10.1215/00703370-9164737

Meta-synthesis : "Qualitative meta-synthesis is a type of qualitative study that uses as data the findings from other qualitative studies linked by the same or related topic." (p.312). Zimmer, L. (2006). Qualitative meta-synthesis: A question of dialoguing with texts .  Journal of Advanced Nursing , 53 (3), 311-318.

• Example : Women’s perspectives on career successes and barriers: A qualitative meta-synthesis:  10.1177/05390184221113735

Literature Reviews in the Health Sciences

• UConn Health subject guide on systematic reviews Explanation of the different review types used in health sciences literature as well as tools to help you find the right review type
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What is a literature review?

A literature review is an integrated analysis -- not just a summary-- of scholarly writings and other relevant evidence related directly to your research question.  That is, it represents a synthesis of the evidence that provides background information on your topic and shows a association between the evidence and your research question.

A literature review may be a stand alone work or the introduction to a larger research paper, depending on the assignment.  Rely heavily on the guidelines your instructor has given you.

Why is it important?

A literature review is important because it:

• Explains the background of research on a topic.
• Demonstrates why a topic is significant to a subject area.
• Discovers relationships between research studies/ideas.
• Identifies major themes, concepts, and researchers on a topic.
• Identifies critical gaps and points of disagreement.
• Discusses further research questions that logically come out of the previous studies.

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APA Style Blog - for those harder to find answers

1. Choose a topic. Define your research question.

Your literature review should be guided by your central research question.  The literature represents background and research developments related to a specific research question, interpreted and analyzed by you in a synthesized way.

• Make sure your research question is not too broad or too narrow.  Is it manageable?
• Begin writing down terms that are related to your question. These will be useful for searches later.
• If you have the opportunity, discuss your topic with your professor and your class mates.

2. Decide on the scope of your review

How many studies do you need to look at? How comprehensive should it be? How many years should it cover? 

• This may depend on your assignment.  How many sources does the assignment require?

3. Select the databases you will use to conduct your searches.

Make a list of the databases you will search. 

Where to find databases:

• use the tabs on this guide
• Find other databases in the Nursing Information Resources web page
• More on the Medical Library web page
• ... and more on the Yale University Library web page

4. Conduct your searches to find the evidence. Keep track of your searches.

• Use the key words in your question, as well as synonyms for those words, as terms in your search. Use the database tutorials for help.
• Save the searches in the databases. This saves time when you want to redo, or modify, the searches. It is also helpful to use as a guide is the searches are not finding any useful results.
• Review the abstracts of research studies carefully. This will save you time.
• Use the bibliographies and references of research studies you find to locate others.
• Check with your professor, or a subject expert in the field, if you are missing any key works in the field.
• Ask your librarian for help at any time.
• Use a citation manager, such as EndNote as the repository for your citations. See the EndNote tutorials for help.

Review the literature

Some questions to help you analyze the research:

• What was the research question of the study you are reviewing? What were the authors trying to discover?
• Was the research funded by a source that could influence the findings?
• What were the research methodologies? Analyze its literature review, the samples and variables used, the results, and the conclusions.
• Does the research seem to be complete? Could it have been conducted more soundly? What further questions does it raise?
• If there are conflicting studies, why do you think that is?
• How are the authors viewed in the field? Has this study been cited? If so, how has it been analyzed?

Tips: 

• Review the abstracts carefully.  
• Keep careful notes so that you may track your thought processes during the research process.
• Create a matrix of the studies for easy analysis, and synthesis, across all of the studies.
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A literature review surveys prior research published in books, scholarly articles, and any other sources relevant to a particular issue, area of research, or theory, and by so doing, provides a description, summary, and critical evaluation of these works in relation to the research problem being investigated. Literature reviews are designed to provide an overview of sources you have used in researching a particular topic and to demonstrate to your readers how your research fits within existing scholarship about the topic.

Fink, Arlene. Conducting Research Literature Reviews: From the Internet to Paper . Fourth edition. Thousand Oaks, CA: SAGE, 2014.

Importance of a Good Literature Review

A literature review may consist of simply a summary of key sources, but in the social sciences, a literature review usually has an organizational pattern and combines both summary and synthesis, often within specific conceptual categories . A summary is a recap of the important information of the source, but a synthesis is a re-organization, or a reshuffling, of that information in a way that informs how you are planning to investigate a research problem. The analytical features of a literature review might:

• Give a new interpretation of old material or combine new with old interpretations,
• Trace the intellectual progression of the field, including major debates,
• Depending on the situation, evaluate the sources and advise the reader on the most pertinent or relevant research, or
• Usually in the conclusion of a literature review, identify where gaps exist in how a problem has been researched to date.

Given this, the purpose of a literature review is to:

• Place each work in the context of its contribution to understanding the research problem being studied.
• Describe the relationship of each work to the others under consideration.
• Identify new ways to interpret prior research.
• Reveal any gaps that exist in the literature.
• Resolve conflicts amongst seemingly contradictory previous studies.
• Identify areas of prior scholarship to prevent duplication of effort.
• Point the way in fulfilling a need for additional research.
• Locate your own research within the context of existing literature [very important].

Fink, Arlene. Conducting Research Literature Reviews: From the Internet to Paper. 2nd ed. Thousand Oaks, CA: Sage, 2005; Hart, Chris. Doing a Literature Review: Releasing the Social Science Research Imagination . Thousand Oaks, CA: Sage Publications, 1998; Jesson, Jill. Doing Your Literature Review: Traditional and Systematic Techniques . Los Angeles, CA: SAGE, 2011; Knopf, Jeffrey W. "Doing a Literature Review." PS: Political Science and Politics 39 (January 2006): 127-132; Ridley, Diana. The Literature Review: A Step-by-Step Guide for Students . 2nd ed. Los Angeles, CA: SAGE, 2012.

Types of Literature Reviews

It is important to think of knowledge in a given field as consisting of three layers. First, there are the primary studies that researchers conduct and publish. Second are the reviews of those studies that summarize and offer new interpretations built from and often extending beyond the primary studies. Third, there are the perceptions, conclusions, opinion, and interpretations that are shared informally among scholars that become part of the body of epistemological traditions within the field.

In composing a literature review, it is important to note that it is often this third layer of knowledge that is cited as "true" even though it often has only a loose relationship to the primary studies and secondary literature reviews. Given this, while literature reviews are designed to provide an overview and synthesis of pertinent sources you have explored, there are a number of approaches you could adopt depending upon the type of analysis underpinning your study.

Argumentative Review This form examines literature selectively in order to support or refute an argument, deeply embedded assumption, or philosophical problem already established in the literature. The purpose is to develop a body of literature that establishes a contrarian viewpoint. Given the value-laden nature of some social science research [e.g., educational reform; immigration control], argumentative approaches to analyzing the literature can be a legitimate and important form of discourse. However, note that they can also introduce problems of bias when they are used to make summary claims of the sort found in systematic reviews [see below].

Integrative Review Considered a form of research that reviews, critiques, and synthesizes representative literature on a topic in an integrated way such that new frameworks and perspectives on the topic are generated. The body of literature includes all studies that address related or identical hypotheses or research problems. A well-done integrative review meets the same standards as primary research in regard to clarity, rigor, and replication. This is the most common form of review in the social sciences.

Historical Review Few things rest in isolation from historical precedent. Historical literature reviews focus on examining research throughout a period of time, often starting with the first time an issue, concept, theory, phenomena emerged in the literature, then tracing its evolution within the scholarship of a discipline. The purpose is to place research in a historical context to show familiarity with state-of-the-art developments and to identify the likely directions for future research.

Methodological Review A review does not always focus on what someone said [findings], but how they came about saying what they say [method of analysis]. Reviewing methods of analysis provides a framework of understanding at different levels [i.e. those of theory, substantive fields, research approaches, and data collection and analysis techniques], how researchers draw upon a wide variety of knowledge ranging from the conceptual level to practical documents for use in fieldwork in the areas of ontological and epistemological consideration, quantitative and qualitative integration, sampling, interviewing, data collection, and data analysis. This approach helps highlight ethical issues which you should be aware of and consider as you go through your own study.

Systematic Review This form consists of an overview of existing evidence pertinent to a clearly formulated research question, which uses pre-specified and standardized methods to identify and critically appraise relevant research, and to collect, report, and analyze data from the studies that are included in the review. The goal is to deliberately document, critically evaluate, and summarize scientifically all of the research about a clearly defined research problem . Typically it focuses on a very specific empirical question, often posed in a cause-and-effect form, such as "To what extent does A contribute to B?" This type of literature review is primarily applied to examining prior research studies in clinical medicine and allied health fields, but it is increasingly being used in the social sciences.

Theoretical Review The purpose of this form is to examine the corpus of theory that has accumulated in regard to an issue, concept, theory, phenomena. The theoretical literature review helps to establish what theories already exist, the relationships between them, to what degree the existing theories have been investigated, and to develop new hypotheses to be tested. Often this form is used to help establish a lack of appropriate theories or reveal that current theories are inadequate for explaining new or emerging research problems. The unit of analysis can focus on a theoretical concept or a whole theory or framework.

NOTE : Most often the literature review will incorporate some combination of types. For example, a review that examines literature supporting or refuting an argument, assumption, or philosophical problem related to the research problem will also need to include writing supported by sources that establish the history of these arguments in the literature.

Baumeister, Roy F. and Mark R. Leary. "Writing Narrative Literature Reviews."  Review of General Psychology 1 (September 1997): 311-320; Mark R. Fink, Arlene. Conducting Research Literature Reviews: From the Internet to Paper . 2nd ed. Thousand Oaks, CA: Sage, 2005; Hart, Chris. Doing a Literature Review: Releasing the Social Science Research Imagination . Thousand Oaks, CA: Sage Publications, 1998; Kennedy, Mary M. "Defining a Literature." Educational Researcher 36 (April 2007): 139-147; Petticrew, Mark and Helen Roberts. Systematic Reviews in the Social Sciences: A Practical Guide . Malden, MA: Blackwell Publishers, 2006; Torracro, Richard. "Writing Integrative Literature Reviews: Guidelines and Examples." Human Resource Development Review 4 (September 2005): 356-367; Rocco, Tonette S. and Maria S. Plakhotnik. "Literature Reviews, Conceptual Frameworks, and Theoretical Frameworks: Terms, Functions, and Distinctions." Human Ressource Development Review 8 (March 2008): 120-130; Sutton, Anthea. Systematic Approaches to a Successful Literature Review . Los Angeles, CA: Sage Publications, 2016.

Structure and Writing Style

I.  Thinking About Your Literature Review

The structure of a literature review should include the following in support of understanding the research problem :

• An overview of the subject, issue, or theory under consideration, along with the objectives of the literature review,
• Division of works under review into themes or categories [e.g. works that support a particular position, those against, and those offering alternative approaches entirely],
• An explanation of how each work is similar to and how it varies from the others,
• Conclusions as to which pieces are best considered in their argument, are most convincing of their opinions, and make the greatest contribution to the understanding and development of their area of research.

The critical evaluation of each work should consider :

• Provenance -- what are the author's credentials? Are the author's arguments supported by evidence [e.g. primary historical material, case studies, narratives, statistics, recent scientific findings]?
• Methodology -- were the techniques used to identify, gather, and analyze the data appropriate to addressing the research problem? Was the sample size appropriate? Were the results effectively interpreted and reported?
• Objectivity -- is the author's perspective even-handed or prejudicial? Is contrary data considered or is certain pertinent information ignored to prove the author's point?
• Persuasiveness -- which of the author's theses are most convincing or least convincing?
• Validity -- are the author's arguments and conclusions convincing? Does the work ultimately contribute in any significant way to an understanding of the subject?

II.  Development of the Literature Review

Four Basic Stages of Writing 1.  Problem formulation -- which topic or field is being examined and what are its component issues? 2.  Literature search -- finding materials relevant to the subject being explored. 3.  Data evaluation -- determining which literature makes a significant contribution to the understanding of the topic. 4.  Analysis and interpretation -- discussing the findings and conclusions of pertinent literature.

Consider the following issues before writing the literature review: Clarify If your assignment is not specific about what form your literature review should take, seek clarification from your professor by asking these questions: 1.  Roughly how many sources would be appropriate to include? 2.  What types of sources should I review (books, journal articles, websites; scholarly versus popular sources)? 3.  Should I summarize, synthesize, or critique sources by discussing a common theme or issue? 4.  Should I evaluate the sources in any way beyond evaluating how they relate to understanding the research problem? 5.  Should I provide subheadings and other background information, such as definitions and/or a history? Find Models Use the exercise of reviewing the literature to examine how authors in your discipline or area of interest have composed their literature review sections. Read them to get a sense of the types of themes you might want to look for in your own research or to identify ways to organize your final review. The bibliography or reference section of sources you've already read, such as required readings in the course syllabus, are also excellent entry points into your own research. Narrow the Topic The narrower your topic, the easier it will be to limit the number of sources you need to read in order to obtain a good survey of relevant resources. Your professor will probably not expect you to read everything that's available about the topic, but you'll make the act of reviewing easier if you first limit scope of the research problem. A good strategy is to begin by searching the USC Libraries Catalog for recent books about the topic and review the table of contents for chapters that focuses on specific issues. You can also review the indexes of books to find references to specific issues that can serve as the focus of your research. For example, a book surveying the history of the Israeli-Palestinian conflict may include a chapter on the role Egypt has played in mediating the conflict, or look in the index for the pages where Egypt is mentioned in the text. Consider Whether Your Sources are Current Some disciplines require that you use information that is as current as possible. This is particularly true in disciplines in medicine and the sciences where research conducted becomes obsolete very quickly as new discoveries are made. However, when writing a review in the social sciences, a survey of the history of the literature may be required. In other words, a complete understanding the research problem requires you to deliberately examine how knowledge and perspectives have changed over time. Sort through other current bibliographies or literature reviews in the field to get a sense of what your discipline expects. You can also use this method to explore what is considered by scholars to be a "hot topic" and what is not.

III.  Ways to Organize Your Literature Review

Chronology of Events If your review follows the chronological method, you could write about the materials according to when they were published. This approach should only be followed if a clear path of research building on previous research can be identified and that these trends follow a clear chronological order of development. For example, a literature review that focuses on continuing research about the emergence of German economic power after the fall of the Soviet Union. By Publication Order your sources by publication chronology, then, only if the order demonstrates a more important trend. For instance, you could order a review of literature on environmental studies of brown fields if the progression revealed, for example, a change in the soil collection practices of the researchers who wrote and/or conducted the studies. Thematic [“conceptual categories”] A thematic literature review is the most common approach to summarizing prior research in the social and behavioral sciences. Thematic reviews are organized around a topic or issue, rather than the progression of time, although the progression of time may still be incorporated into a thematic review. For example, a review of the Internet’s impact on American presidential politics could focus on the development of online political satire. While the study focuses on one topic, the Internet’s impact on American presidential politics, it would still be organized chronologically reflecting technological developments in media. The difference in this example between a "chronological" and a "thematic" approach is what is emphasized the most: themes related to the role of the Internet in presidential politics. Note that more authentic thematic reviews tend to break away from chronological order. A review organized in this manner would shift between time periods within each section according to the point being made. Methodological A methodological approach focuses on the methods utilized by the researcher. For the Internet in American presidential politics project, one methodological approach would be to look at cultural differences between the portrayal of American presidents on American, British, and French websites. Or the review might focus on the fundraising impact of the Internet on a particular political party. A methodological scope will influence either the types of documents in the review or the way in which these documents are discussed.

Other Sections of Your Literature Review Once you've decided on the organizational method for your literature review, the sections you need to include in the paper should be easy to figure out because they arise from your organizational strategy. In other words, a chronological review would have subsections for each vital time period; a thematic review would have subtopics based upon factors that relate to the theme or issue. However, sometimes you may need to add additional sections that are necessary for your study, but do not fit in the organizational strategy of the body. What other sections you include in the body is up to you. However, only include what is necessary for the reader to locate your study within the larger scholarship about the research problem.

Here are examples of other sections, usually in the form of a single paragraph, you may need to include depending on the type of review you write:

• Current Situation : Information necessary to understand the current topic or focus of the literature review.
• Sources Used : Describes the methods and resources [e.g., databases] you used to identify the literature you reviewed.
• History : The chronological progression of the field, the research literature, or an idea that is necessary to understand the literature review, if the body of the literature review is not already a chronology.
• Selection Methods : Criteria you used to select (and perhaps exclude) sources in your literature review. For instance, you might explain that your review includes only peer-reviewed [i.e., scholarly] sources.
• Standards : Description of the way in which you present your information.
• Questions for Further Research : What questions about the field has the review sparked? How will you further your research as a result of the review?

IV.  Writing Your Literature Review

Once you've settled on how to organize your literature review, you're ready to write each section. When writing your review, keep in mind these issues.

Use Evidence A literature review section is, in this sense, just like any other academic research paper. Your interpretation of the available sources must be backed up with evidence [citations] that demonstrates that what you are saying is valid. Be Selective Select only the most important points in each source to highlight in the review. The type of information you choose to mention should relate directly to the research problem, whether it is thematic, methodological, or chronological. Related items that provide additional information, but that are not key to understanding the research problem, can be included in a list of further readings . Use Quotes Sparingly Some short quotes are appropriate if you want to emphasize a point, or if what an author stated cannot be easily paraphrased. Sometimes you may need to quote certain terminology that was coined by the author, is not common knowledge, or taken directly from the study. Do not use extensive quotes as a substitute for using your own words in reviewing the literature. Summarize and Synthesize Remember to summarize and synthesize your sources within each thematic paragraph as well as throughout the review. Recapitulate important features of a research study, but then synthesize it by rephrasing the study's significance and relating it to your own work and the work of others. Keep Your Own Voice While the literature review presents others' ideas, your voice [the writer's] should remain front and center. For example, weave references to other sources into what you are writing but maintain your own voice by starting and ending the paragraph with your own ideas and wording. Use Caution When Paraphrasing When paraphrasing a source that is not your own, be sure to represent the author's information or opinions accurately and in your own words. Even when paraphrasing an author’s work, you still must provide a citation to that work.

V.  Common Mistakes to Avoid

These are the most common mistakes made in reviewing social science research literature.

• Sources in your literature review do not clearly relate to the research problem;
• You do not take sufficient time to define and identify the most relevant sources to use in the literature review related to the research problem;
• Relies exclusively on secondary analytical sources rather than including relevant primary research studies or data;
• Uncritically accepts another researcher's findings and interpretations as valid, rather than examining critically all aspects of the research design and analysis;
• Does not describe the search procedures that were used in identifying the literature to review;
• Reports isolated statistical results rather than synthesizing them in chi-squared or meta-analytic methods; and,
• Only includes research that validates assumptions and does not consider contrary findings and alternative interpretations found in the literature.

Cook, Kathleen E. and Elise Murowchick. “Do Literature Review Skills Transfer from One Course to Another?” Psychology Learning and Teaching 13 (March 2014): 3-11; Fink, Arlene. Conducting Research Literature Reviews: From the Internet to Paper . 2nd ed. Thousand Oaks, CA: Sage, 2005; Hart, Chris. Doing a Literature Review: Releasing the Social Science Research Imagination . Thousand Oaks, CA: Sage Publications, 1998; Jesson, Jill. Doing Your Literature Review: Traditional and Systematic Techniques . London: SAGE, 2011; Literature Review Handout. Online Writing Center. Liberty University; Literature Reviews. The Writing Center. University of North Carolina; Onwuegbuzie, Anthony J. and Rebecca Frels. Seven Steps to a Comprehensive Literature Review: A Multimodal and Cultural Approach . Los Angeles, CA: SAGE, 2016; Ridley, Diana. The Literature Review: A Step-by-Step Guide for Students . 2nd ed. Los Angeles, CA: SAGE, 2012; Randolph, Justus J. “A Guide to Writing the Dissertation Literature Review." Practical Assessment, Research, and Evaluation. vol. 14, June 2009; Sutton, Anthea. Systematic Approaches to a Successful Literature Review . Los Angeles, CA: Sage Publications, 2016; Taylor, Dena. The Literature Review: A Few Tips On Conducting It. University College Writing Centre. University of Toronto; Writing a Literature Review. Academic Skills Centre. University of Canberra.

Writing Tip

Break Out of Your Disciplinary Box!

Thinking interdisciplinarily about a research problem can be a rewarding exercise in applying new ideas, theories, or concepts to an old problem. For example, what might cultural anthropologists say about the continuing conflict in the Middle East? In what ways might geographers view the need for better distribution of social service agencies in large cities than how social workers might study the issue? You don’t want to substitute a thorough review of core research literature in your discipline for studies conducted in other fields of study. However, particularly in the social sciences, thinking about research problems from multiple vectors is a key strategy for finding new solutions to a problem or gaining a new perspective. Consult with a librarian about identifying research databases in other disciplines; almost every field of study has at least one comprehensive database devoted to indexing its research literature.

Frodeman, Robert. The Oxford Handbook of Interdisciplinarity . New York: Oxford University Press, 2010.

Another Writing Tip

Don't Just Review for Content!

While conducting a review of the literature, maximize the time you devote to writing this part of your paper by thinking broadly about what you should be looking for and evaluating. Review not just what scholars are saying, but how are they saying it. Some questions to ask:

• How are they organizing their ideas?
• What methods have they used to study the problem?
• What theories have been used to explain, predict, or understand their research problem?
• What sources have they cited to support their conclusions?
• How have they used non-textual elements [e.g., charts, graphs, figures, etc.] to illustrate key points?

When you begin to write your literature review section, you'll be glad you dug deeper into how the research was designed and constructed because it establishes a means for developing more substantial analysis and interpretation of the research problem.

Hart, Chris. Doing a Literature Review: Releasing the Social Science Research Imagination . Thousand Oaks, CA: Sage Publications, 1 998.

Yet Another Writing Tip

When Do I Know I Can Stop Looking and Move On?

Here are several strategies you can utilize to assess whether you've thoroughly reviewed the literature:

• Look for repeating patterns in the research findings . If the same thing is being said, just by different people, then this likely demonstrates that the research problem has hit a conceptual dead end. At this point consider: Does your study extend current research?  Does it forge a new path? Or, does is merely add more of the same thing being said?
• Look at sources the authors cite to in their work . If you begin to see the same researchers cited again and again, then this is often an indication that no new ideas have been generated to address the research problem.
• Search Google Scholar to identify who has subsequently cited leading scholars already identified in your literature review [see next sub-tab]. This is called citation tracking and there are a number of sources that can help you identify who has cited whom, particularly scholars from outside of your discipline. Here again, if the same authors are being cited again and again, this may indicate no new literature has been written on the topic.

Onwuegbuzie, Anthony J. and Rebecca Frels. Seven Steps to a Comprehensive Literature Review: A Multimodal and Cultural Approach . Los Angeles, CA: Sage, 2016; Sutton, Anthea. Systematic Approaches to a Successful Literature Review . Los Angeles, CA: Sage Publications, 2016.

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Research Methods

• Getting Started
• Literature Review Research
• Research Design
• Research Design By Discipline
• SAGE Research Methods
• Teaching with SAGE Research Methods

Literature Review

• What is a Literature Review?
• What is NOT a Literature Review?
• Purposes of a Literature Review
• Types of Literature Reviews
• Literature Reviews vs. Systematic Reviews
• Systematic vs. Meta-Analysis

Literature Review  is a comprehensive survey of the works published in a particular field of study or line of research, usually over a specific period of time, in the form of an in-depth, critical bibliographic essay or annotated list in which attention is drawn to the most significant works.

Also, we can define a literature review as the collected body of scholarly works related to a topic:

• Summarizes and analyzes previous research relevant to a topic
• Includes scholarly books and articles published in academic journals
• Can be an specific scholarly paper or a section in a research paper

The objective of a Literature Review is to find previous published scholarly works relevant to an specific topic

• Help gather ideas or information
• Keep up to date in current trends and findings
• Help develop new questions

A literature review is important because it:

• Explains the background of research on a topic.
• Demonstrates why a topic is significant to a subject area.
• Helps focus your own research questions or problems
• Discovers relationships between research studies/ideas.
• Suggests unexplored ideas or populations
• Identifies major themes, concepts, and researchers on a topic.
• Tests assumptions; may help counter preconceived ideas and remove unconscious bias.
• Identifies critical gaps, points of disagreement, or potentially flawed methodology or theoretical approaches.
• Indicates potential directions for future research.

All content in this section is from Literature Review Research from Old Dominion University 

Keep in mind the following, a literature review is NOT:

Not an essay 

Not an annotated bibliography  in which you summarize each article that you have reviewed.  A literature review goes beyond basic summarizing to focus on the critical analysis of the reviewed works and their relationship to your research question.

Not a research paper   where you select resources to support one side of an issue versus another.  A lit review should explain and consider all sides of an argument in order to avoid bias, and areas of agreement and disagreement should be highlighted.

A literature review serves several purposes. For example, it

• provides thorough knowledge of previous studies; introduces seminal works.
• helps focus one’s own research topic.
• identifies a conceptual framework for one’s own research questions or problems; indicates potential directions for future research.
• suggests previously unused or underused methodologies, designs, quantitative and qualitative strategies.
• identifies gaps in previous studies; identifies flawed methodologies and/or theoretical approaches; avoids replication of mistakes.
• helps the researcher avoid repetition of earlier research.
• suggests unexplored populations.
• determines whether past studies agree or disagree; identifies controversy in the literature.
• tests assumptions; may help counter preconceived ideas and remove unconscious bias.

As Kennedy (2007) notes*, it is important to think of knowledge in a given field as consisting of three layers. First, there are the primary studies that researchers conduct and publish. Second are the reviews of those studies that summarize and offer new interpretations built from and often extending beyond the original studies. Third, there are the perceptions, conclusions, opinion, and interpretations that are shared informally that become part of the lore of field. In composing a literature review, it is important to note that it is often this third layer of knowledge that is cited as "true" even though it often has only a loose relationship to the primary studies and secondary literature reviews.

Given this, while literature reviews are designed to provide an overview and synthesis of pertinent sources you have explored, there are several approaches to how they can be done, depending upon the type of analysis underpinning your study. Listed below are definitions of types of literature reviews:

Argumentative Review      This form examines literature selectively in order to support or refute an argument, deeply imbedded assumption, or philosophical problem already established in the literature. The purpose is to develop a body of literature that establishes a contrarian viewpoint. Given the value-laden nature of some social science research [e.g., educational reform; immigration control], argumentative approaches to analyzing the literature can be a legitimate and important form of discourse. However, note that they can also introduce problems of bias when they are used to to make summary claims of the sort found in systematic reviews.

Integrative Review      Considered a form of research that reviews, critiques, and synthesizes representative literature on a topic in an integrated way such that new frameworks and perspectives on the topic are generated. The body of literature includes all studies that address related or identical hypotheses. A well-done integrative review meets the same standards as primary research in regard to clarity, rigor, and replication.

Historical Review      Few things rest in isolation from historical precedent. Historical reviews are focused on examining research throughout a period of time, often starting with the first time an issue, concept, theory, phenomena emerged in the literature, then tracing its evolution within the scholarship of a discipline. The purpose is to place research in a historical context to show familiarity with state-of-the-art developments and to identify the likely directions for future research.

Methodological Review      A review does not always focus on what someone said [content], but how they said it [method of analysis]. This approach provides a framework of understanding at different levels (i.e. those of theory, substantive fields, research approaches and data collection and analysis techniques), enables researchers to draw on a wide variety of knowledge ranging from the conceptual level to practical documents for use in fieldwork in the areas of ontological and epistemological consideration, quantitative and qualitative integration, sampling, interviewing, data collection and data analysis, and helps highlight many ethical issues which we should be aware of and consider as we go through our study.

Systematic Review      This form consists of an overview of existing evidence pertinent to a clearly formulated research question, which uses pre-specified and standardized methods to identify and critically appraise relevant research, and to collect, report, and analyse data from the studies that are included in the review. Typically it focuses on a very specific empirical question, often posed in a cause-and-effect form, such as "To what extent does A contribute to B?"

Theoretical Review      The purpose of this form is to concretely examine the corpus of theory that has accumulated in regard to an issue, concept, theory, phenomena. The theoretical literature review help establish what theories already exist, the relationships between them, to what degree the existing theories have been investigated, and to develop new hypotheses to be tested. Often this form is used to help establish a lack of appropriate theories or reveal that current theories are inadequate for explaining new or emerging research problems. The unit of analysis can focus on a theoretical concept or a whole theory or framework.

* Kennedy, Mary M. "Defining a Literature."  Educational Researcher  36 (April 2007): 139-147.

All content in this section is from The Literature Review created by Dr. Robert Larabee USC

Robinson, P. and Lowe, J. (2015),  Literature reviews vs systematic reviews.  Australian and New Zealand Journal of Public Health, 39: 103-103. doi: 10.1111/1753-6405.12393

What's in the name? The difference between a Systematic Review and a Literature Review, and why it matters . By Lynn Kysh from University of Southern California

Systematic review or meta-analysis?

A  systematic review  answers a defined research question by collecting and summarizing all empirical evidence that fits pre-specified eligibility criteria.

A  meta-analysis  is the use of statistical methods to summarize the results of these studies.

Systematic reviews, just like other research articles, can be of varying quality. They are a significant piece of work (the Centre for Reviews and Dissemination at York estimates that a team will take 9-24 months), and to be useful to other researchers and practitioners they should have:

• clearly stated objectives with pre-defined eligibility criteria for studies
• explicit, reproducible methodology
• a systematic search that attempts to identify all studies
• assessment of the validity of the findings of the included studies (e.g. risk of bias)
• systematic presentation, and synthesis, of the characteristics and findings of the included studies

Not all systematic reviews contain meta-analysis. 

Meta-analysis is the use of statistical methods to summarize the results of independent studies. By combining information from all relevant studies, meta-analysis can provide more precise estimates of the effects of health care than those derived from the individual studies included within a review.  More information on meta-analyses can be found in  Cochrane Handbook, Chapter 9 .

A meta-analysis goes beyond critique and integration and conducts secondary statistical analysis on the outcomes of similar studies.  It is a systematic review that uses quantitative methods to synthesize and summarize the results.

An advantage of a meta-analysis is the ability to be completely objective in evaluating research findings.  Not all topics, however, have sufficient research evidence to allow a meta-analysis to be conducted.  In that case, an integrative review is an appropriate strategy. 

Some of the content in this section is from Systematic reviews and meta-analyses: step by step guide created by Kate McAllister.

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Frequently asked questions

What is the purpose of a literature review.

There are several reasons to conduct a literature review at the beginning of a research project:

• To familiarize yourself with the current state of knowledge on your topic
• To ensure that you’re not just repeating what others have already done
• To identify gaps in knowledge and unresolved problems that your research can address
• To develop your theoretical framework and methodology
• To provide an overview of the key findings and debates on the topic

Writing the literature review shows your reader how your work relates to existing research and what new insights it will contribute.

Frequently asked questions: Academic writing

A rhetorical tautology is the repetition of an idea of concept using different words.

Rhetorical tautologies occur when additional words are used to convey a meaning that has already been expressed or implied. For example, the phrase “armed gunman” is a tautology because a “gunman” is by definition “armed.”

A logical tautology is a statement that is always true because it includes all logical possibilities.

Logical tautologies often take the form of “either/or” statements (e.g., “It will rain, or it will not rain”) or employ circular reasoning (e.g., “she is untrustworthy because she can’t be trusted”).

You may have seen both “appendices” or “appendixes” as pluralizations of “ appendix .” Either spelling can be used, but “appendices” is more common (including in APA Style ). Consistency is key here: make sure you use the same spelling throughout your paper.

The purpose of a lab report is to demonstrate your understanding of the scientific method with a hands-on lab experiment. Course instructors will often provide you with an experimental design and procedure. Your task is to write up how you actually performed the experiment and evaluate the outcome.

In contrast, a research paper requires you to independently develop an original argument. It involves more in-depth research and interpretation of sources and data.

A lab report is usually shorter than a research paper.

The sections of a lab report can vary between scientific fields and course requirements, but it usually contains the following:

• Title: expresses the topic of your study
• Abstract: summarizes your research aims, methods, results, and conclusions
• Introduction: establishes the context needed to understand the topic
• Method: describes the materials and procedures used in the experiment
• Results: reports all descriptive and inferential statistical analyses
• Discussion: interprets and evaluates results and identifies limitations
• Conclusion: sums up the main findings of your experiment
• References: list of all sources cited using a specific style (e.g. APA)
• Appendices: contains lengthy materials, procedures, tables or figures

A lab report conveys the aim, methods, results, and conclusions of a scientific experiment . Lab reports are commonly assigned in science, technology, engineering, and mathematics (STEM) fields.

The abstract is the very last thing you write. You should only write it after your research is complete, so that you can accurately summarize the entirety of your thesis , dissertation or research paper .

If you’ve gone over the word limit set for your assignment, shorten your sentences and cut repetition and redundancy during the editing process. If you use a lot of long quotes , consider shortening them to just the essentials.

If you need to remove a lot of words, you may have to cut certain passages. Remember that everything in the text should be there to support your argument; look for any information that’s not essential to your point and remove it.

To make this process easier and faster, you can use a paraphrasing tool . With this tool, you can rewrite your text to make it simpler and shorter. If that’s not enough, you can copy-paste your paraphrased text into the summarizer . This tool will distill your text to its core message.

Revising, proofreading, and editing are different stages of the writing process .

• Revising is making structural and logical changes to your text—reformulating arguments and reordering information.
• Editing refers to making more local changes to things like sentence structure and phrasing to make sure your meaning is conveyed clearly and concisely.
• Proofreading involves looking at the text closely, line by line, to spot any typos and issues with consistency and correct them.

The literature review usually comes near the beginning of your thesis or dissertation . After the introduction , it grounds your research in a scholarly field and leads directly to your theoretical framework or methodology .

A literature review is a survey of scholarly sources (such as books, journal articles, and theses) related to a specific topic or research question .

It is often written as part of a thesis, dissertation , or research paper , in order to situate your work in relation to existing knowledge.

Avoid citing sources in your abstract . There are two reasons for this:

• The abstract should focus on your original research, not on the work of others.
• The abstract should be self-contained and fully understandable without reference to other sources.

There are some circumstances where you might need to mention other sources in an abstract: for example, if your research responds directly to another study or focuses on the work of a single theorist. In general, though, don’t include citations unless absolutely necessary.

An abstract is a concise summary of an academic text (such as a journal article or dissertation ). It serves two main purposes:

• To help potential readers determine the relevance of your paper for their own research.
• To communicate your key findings to those who don’t have time to read the whole paper.

Abstracts are often indexed along with keywords on academic databases, so they make your work more easily findable. Since the abstract is the first thing any reader sees, it’s important that it clearly and accurately summarizes the contents of your paper.

In a scientific paper, the methodology always comes after the introduction and before the results , discussion and conclusion . The same basic structure also applies to a thesis, dissertation , or research proposal .

Depending on the length and type of document, you might also include a literature review or theoretical framework before the methodology.

Whether you’re publishing a blog, submitting a research paper , or even just writing an important email, there are a few techniques you can use to make sure it’s error-free:

• Take a break : Set your work aside for at least a few hours so that you can look at it with fresh eyes.
• Proofread a printout : Staring at a screen for too long can cause fatigue – sit down with a pen and paper to check the final version.
• Use digital shortcuts : Take note of any recurring mistakes (for example, misspelling a particular word, switching between US and UK English , or inconsistently capitalizing a term), and use Find and Replace to fix it throughout the document.

If you want to be confident that an important text is error-free, it might be worth choosing a professional proofreading service instead.

Editing and proofreading are different steps in the process of revising a text.

Editing comes first, and can involve major changes to content, structure and language. The first stages of editing are often done by authors themselves, while a professional editor makes the final improvements to grammar and style (for example, by improving sentence structure and word choice ).

Proofreading is the final stage of checking a text before it is published or shared. It focuses on correcting minor errors and inconsistencies (for example, in punctuation and capitalization ). Proofreaders often also check for formatting issues, especially in print publishing.

The cost of proofreading depends on the type and length of text, the turnaround time, and the level of services required. Most proofreading companies charge per word or page, while freelancers sometimes charge an hourly rate.

For proofreading alone, which involves only basic corrections of typos and formatting mistakes, you might pay as little as $0.01 per word, but in many cases, your text will also require some level of editing , which costs slightly more.

It’s often possible to purchase combined proofreading and editing services and calculate the price in advance based on your requirements.

There are many different routes to becoming a professional proofreader or editor. The necessary qualifications depend on the field – to be an academic or scientific proofreader, for example, you will need at least a university degree in a relevant subject.

For most proofreading jobs, experience and demonstrated skills are more important than specific qualifications. Often your skills will be tested as part of the application process.

To learn practical proofreading skills, you can choose to take a course with a professional organization such as the Society for Editors and Proofreaders . Alternatively, you can apply to companies that offer specialized on-the-job training programmes, such as the Scribbr Academy .

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Learn how to write a review of literature

What is a review of literature.

The format of a review of literature may vary from discipline to discipline and from assignment to assignment.

A review may be a self-contained unit — an end in itself — or a preface to and rationale for engaging in primary research. A review is a required part of grant and research proposals and often a chapter in theses and dissertations.

Generally, the purpose of a review is to analyze critically a segment of a published body of knowledge through summary, classification, and comparison of prior research studies, reviews of literature, and theoretical articles.

Writing the introduction

In the introduction, you should:

Define or identify the general topic, issue, or area of concern, thus providing an appropriate context for reviewing the literature.

Point out overall trends in what has been published about the topic; or conflicts in theory, methodology, evidence, and conclusions; or gaps in research and scholarship; or a single problem or new perspective of immediate interest.

Establish the writer’s reason (point of view) for reviewing the literature; explain the criteria to be used in analyzing and comparing literature and the organization of the review (sequence); and, when necessary, state why certain literature is or is not included (scope).

Writing the body

In the body, you should:

Group research studies and other types of literature (reviews, theoretical articles, case studies, etc.) according to common denominators such as qualitative versus quantitative approaches, conclusions of authors, specific purpose or objective, chronology, etc.

Summarize individual studies or articles with as much or as little detail as each merits according to its comparative importance in the literature, remembering that space (length) denotes significance.

Provide the reader with strong “umbrella” sentences at beginnings of paragraphs, “signposts” throughout, and brief “so what” summary sentences at intermediate points in the review to aid in understanding comparisons and analyses.

Writing the conclusion

In the conclusion, you should:

Summarize major contributions of significant studies and articles to the body of knowledge under review, maintaining the focus established in the introduction.

Evaluate the current “state of the art” for the body of knowledge reviewed, pointing out major methodological flaws or gaps in research, inconsistencies in theory and findings, and areas or issues pertinent to future study.

Conclude by providing some insight into the relationship between the central topic of the literature review and a larger area of study such as a discipline, a scientific endeavor, or a profession.

For further information see our handouts on Writing a Critical Review of a Nonfiction Book or Article or Reading a Book to Review It .

To learn more about literature reviews, take a look at our workshop on Writing Literature Reviews of Published Research.

Sample Literature Reviews

An important strategy for learning how to compose literature reviews in your field or within a specific genre is to locate and analyze representative examples. The following collection of annotated sample literature reviews written and co-written by colleagues associated with UW-Madison showcases how these reviews can do different kind of work for different purposes. Use these successful examples as a starting point for understanding how other writers have approached the challenging and important task of situating their idea in the context of established research.

• Sample 1 (PDF) A brief literature review within a political scientists’  National Science Foundation Graduate Research Fellowship  grant
• Sample 2 (PDF) A several-page literature review at the beginning of a published, academic article about philosophy
• Sample 3 (PDF) A brief literature review at the beginning of a published, academic article about photochemistry

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What is a Literature Review?

A literature or narrative review is a comprehensive review and analysis of the published literature on a specific topic or research question. The literature that is reviewed contains: books, articles, academic articles, conference proceedings, association papers, and dissertations. It contains the most pertinent studies and points to important past and current research and practices. It provides background and context, and shows how your research will contribute to the field. 

A literature review should: 

• Provide a comprehensive and updated review of the literature;
• Explain why this review has taken place;
• Articulate a position or hypothesis;
• Acknowledge and account for conflicting and corroborating points of view

From  S age Research Methods

Purpose of a Literature Review

A literature review can be written as an introduction to a study to:

• Demonstrate how a study fills a gap in research
• Compare a study with other research that's been done

Or it can be a separate work (a research article on its own) which:

• Organizes or describes a topic
• Describes variables within a particular issue/problem

Limitations of a Literature Review

Some of the limitations of a literature review are:

• It's a snapshot in time. Unlike other reviews, this one has beginning, a middle and an end. There may be future developments that could make your work less relevant.
• It may be too focused. Some niche studies may miss the bigger picture.
• It can be difficult to be comprehensive. There is no way to make sure all the literature on a topic was considered.
• It is easy to be biased if you stick to top tier journals. There may be other places where people are publishing exemplary research. Look to open access publications and conferences to reflect a more inclusive collection. Also, make sure to include opposing views (and not just supporting evidence).

Source: Grant, Maria J., and Andrew Booth. “A Typology of Reviews: An Analysis of 14 Review Types and Associated Methodologies.” Health Information & Libraries Journal, vol. 26, no. 2, June 2009, pp. 91–108. Wiley Online Library, doi:10.1111/j.1471-1842.2009.00848.x.

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For help in other subject areas, please see the guide to library specialists by subject .

Periodically, UT Libraries runs a workshop covering the basics and library support for literature reviews. While we try to offer these once per academic year, we find providing the recording to be helpful to community members who have missed the session. Following is the most recent recording of the workshop, Conducting a Literature Review. To view the recording, a UT login is required.

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Educational resources and simple solutions for your research journey

How to write review of related literature (RRL) in research

A review of related literature (a.k.a RRL in research) is a comprehensive review of the existing literature pertaining to a specific topic or research question. An effective review provides the reader with an organized analysis and synthesis of the existing knowledge about a subject. With the increasing amount of new information being disseminated every day, conducting a review of related literature is becoming more difficult and the purpose of review of related literature is clearer than ever.  

All new knowledge is necessarily based on previously known information, and every new scientific study must be conducted and reported in the context of previous studies. This makes a review of related literature essential for research, and although it may be tedious work at times , most researchers will complete many such reviews of varying depths during their career. So, why exactly is a review of related literature important?    

Table of Contents

Why a review of related literature in research is important  

Before thinking how to do reviews of related literature , it is necessary to understand its importance. Although the purpose of a review of related literature varies depending on the discipline and how it will be used, its importance is never in question. Here are some ways in which a review can be crucial.  

• Identify gaps in the knowledge – This is the primary purpose of a review of related literature (often called RRL in research ). To create new knowledge, you must first determine what knowledge may be missing. This also helps to identify the scope of your study.  
• Avoid duplication of research efforts – Not only will a review of related literature indicate gaps in the existing research, but it will also lead you away from duplicating research that has already been done and thus save precious resources.  
• Provide an overview of disparate and interdisciplinary research areas – Researchers cannot possibly know everything related to their disciplines. Therefore, it is very helpful to have access to a review of related literature already written and published.  
• Highlight researcher’s familiarity with their topic 1  – A strong review of related literature in a study strengthens readers’ confidence in that study and that researcher.

Tips on how to write a review of related literature in research

Given that you will probably need to produce a number of these at some point, here are a few general tips on how to write an effective review of related literature 2 .

• Define your topic, audience, and purpose: You will be spending a lot of time with this review, so choose a topic that is interesting to you. While deciding what to write in a review of related literature , think about who you expect to read the review – researchers in your discipline, other scientists, the general public – and tailor the language to the audience. Also, think about the purpose of your review of related literature .  
• Conduct a comprehensive literature search: While writing your review of related literature , emphasize more recent works but don’t forget to include some older publications as well. Cast a wide net, as you may find some interesting and relevant literature in unexpected databases or library corners. Don’t forget to search for recent conference papers.
• Review the identified articles and take notes: It is a good idea to take notes in a way such that individual items in your notes can be moved around when you organize them. For example, index cards are great tools for this. Write each individual idea on a separate card along with the source. The cards can then be easily grouped and organized.  
• Determine how to organize your review: A review of related literature should not be merely a listing of descriptions. It should be organized by some criterion, such as chronologically or thematically.  
• Be critical and objective: Don’t just report the findings of other studies in your review of related literature . Challenge the methodology, find errors in the analysis, question the conclusions. Use what you find to improve your research. However, do not insert your opinions into the review of related literature. Remain objective and open-minded.  
• Structure your review logically: Guide the reader through the information. The structure will depend on the function of the review of related literature. Creating an outline prior to writing the RRL in research is a good way to ensure the presented information flows well.  

As you read more extensively in your discipline, you will notice that the review of related literature appears in various forms in different places. For example, when you read an article about an experimental study, you will typically see a literature review or a RRL in research , in the introduction that includes brief descriptions of similar studies. In longer research studies and dissertations, especially in the social sciences, the review of related literature will typically be a separate chapter and include more information on methodologies and theory building. In addition, stand-alone review articles will be published that are extremely useful to researchers.  

The review of relevant literature or often abbreviated as, RRL in research , is an important communication tool that can be used in many forms for many purposes. It is a tool that all researchers should befriend.  

• University of North Carolina at Chapel Hill Writing Center. Literature Reviews.  https://writingcenter.unc.edu/tips-and-tools/literature-reviews/  [Accessed September 8, 2022]
• Pautasso M. Ten simple rules for writing a literature review. PLoS Comput Biol. 2013, 9. doi: 10.1371/journal.pcbi.1003149.

Q:  Is research complete without a review of related literature?

A research project is usually considered incomplete without a proper review of related literature. The review of related literature is a crucial component of any research project as it provides context for the research question, identifies gaps in existing literature, and ensures novelty by avoiding duplication. It also helps inform research design and supports arguments, highlights the significance of a study, and demonstrates your knowledge an expertise.

Q: What is difference between RRL and RRS?

The key difference between an RRL and an RRS lies in their focus and scope. An RRL or review of related literature examines a broad range of literature, including theoretical frameworks, concepts, and empirical studies, to establish the context and significance of the research topic. On the other hand, an RRS or review of research studies specifically focuses on analyzing and summarizing previous research studies within a specific research domain to gain insights into methodologies, findings, and gaps in the existing body of knowledge. While there may be some overlap between the two, they serve distinct purposes and cover different aspects of the research process.

Q: Does review of related literature improve accuracy and validity of research?

Yes, a comprehensive review of related literature (RRL) plays a vital role in improving the accuracy and validity of research. It helps authors gain a deeper understanding and offers different perspectives on the research topic. RRL can help you identify research gaps, dictate the selection of appropriate research methodologies, enhance theoretical frameworks, avoid biases and errors, and even provide support for research design and interpretation. By building upon and critically engaging with existing related literature, researchers can ensure their work is rigorous, reliable, and contributes meaningfully to their field of study.

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Research on research? If you find this idea rather peculiar, know that nowadays, with the huge amount of information produced daily all around the world, it is becoming more and more difficult to keep up to date with all of it. In addition to the sheer amount of research, there is also its origin. We are witnessing the economic and intellectual emergence of countries like China, Brazil, Turkey, and United Arab Emirates, for example, that are producing scholarly literature in their own languages. So, apart from the effort of gathering information, there must also be translators prepared to unify all of it in a single language to be the object of the literature survey. At Elsevier, our team of translators is ready to support researchers by delivering high-quality scientific translations , in several languages, to serve their research – no matter the topic.

What is a literature review?

A literature review is a study – or, more accurately, a survey – involving scholarly material, with the aim to discuss published information about a specific topic or research question. Therefore, to write a literature review, it is compulsory that you are a real expert in the object of study. The results and findings will be published and made available to the public, namely scientists working in the same area of research.

How to Write a Literature Review

First of all, don’t forget that writing a literature review is a great responsibility. It’s a document that is expected to be highly reliable, especially concerning its sources and findings. You have to feel intellectually comfortable in the area of study and highly proficient in the target language; misconceptions and errors do not have a place in a document as important as a literature review. In fact, you might want to consider text editing services, like those offered at Elsevier, to make sure your literature is following the highest standards of text quality. You want to make sure your literature review is memorable by its novelty and quality rather than language errors.

Writing a literature review requires expertise but also organization. We cannot teach you about your topic of research, but we can provide a few steps to guide you through conducting a literature review:

• Choose your topic or research question: It should not be too comprehensive or too limited. You have to complete your task within a feasible time frame.
• Set the scope: Define boundaries concerning the number of sources, time frame to be covered, geographical area, etc.
• Decide which databases you will use for your searches: In order to search the best viable sources for your literature review, use highly regarded, comprehensive databases to get a big picture of the literature related to your topic.
• Search, search, and search: Now you’ll start to investigate the research on your topic. It’s critical that you keep track of all the sources. Start by looking at research abstracts in detail to see if their respective studies relate to or are useful for your own work. Next, search for bibliographies and references that can help you broaden your list of resources. Choose the most relevant literature and remember to keep notes of their bibliographic references to be used later on.
• Review all the literature, appraising carefully it’s content: After reading the study’s abstract, pay attention to the rest of the content of the articles you deem the “most relevant.” Identify methodologies, the most important questions they address, if they are well-designed and executed, and if they are cited enough, etc.

If it’s the first time you’ve published a literature review, note that it is important to follow a special structure. Just like in a thesis, for example, it is expected that you have an introduction – giving the general idea of the central topic and organizational pattern – a body – which contains the actual discussion of the sources – and finally the conclusion or recommendations – where you bring forward whatever you have drawn from the reviewed literature. The conclusion may even suggest there are no agreeable findings and that the discussion should be continued.

Why are literature reviews important?

Literature reviews constantly feed new research, that constantly feeds literature reviews…and we could go on and on. The fact is, one acts like a force over the other and this is what makes science, as a global discipline, constantly develop and evolve. As a scientist, writing a literature review can be very beneficial to your career, and set you apart from the expert elite in your field of interest. But it also can be an overwhelming task, so don’t hesitate in contacting Elsevier for text editing services, either for profound edition or just a last revision. We guarantee the very highest standards. You can also save time by letting us suggest and make the necessary amendments to your manuscript, so that it fits the structural pattern of a literature review. Who knows how many worldwide researchers you will impact with your next perfectly written literature review.

Know more: How to Find a Gap in Research .

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Literature Reviews within a Scholarly Work

Literature reviews as a scholarly work.

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Literature reviews summarize and analyze what has been written on a particular topic and identify gaps or disagreements in the scholarly work on that topic.

Within a scholarly work, the literature review situates the current work within the larger scholarly conversation and emphasizes how that particular scholarly work contributes to the conversation on the topic. The literature review portion may be as brief as a few paragraphs focusing on a narrow topic area.

When writing this type of literature review, it's helpful to start by identifying sources most relevant to your research question. A citation tracking database such as Web of Science can also help you locate seminal articles on a topic and find out who has more recently cited them. See "Your Literature Search" for more details.

A literature review may itself be a scholarly publication and provide an analysis of what has been written on a particular topic without contributing original research. These types of literature reviews can serve to help keep people updated on a field as well as helping scholars choose a research topic to fill gaps in the knowledge on that topic. Common types include:

Systematic Review

Systematic literature reviews follow specific procedures in some ways similar to setting up an experiment to ensure that future scholars can replicate the same steps. They are also helpful for evaluating data published over multiple studies. Thus, these are common in the medical field and may be used by healthcare providers to help guide diagnosis and treatment decisions. Cochrane Reviews are one example of this type of literature review.

Semi-Systematic Review

When a systematic review is not feasible, a semi-systematic review can help synthesize research on a topic or how a topic has been studied in different fields (Snyder 2019). Rather than focusing on quantitative data, this review type identifies themes, theoretical perspectives, and other qualitative information related to the topic. These types of reviews can be particularly helpful for a historical topic overview, for developing a theoretical model, and for creating a research agenda for a field (Snyder 2019). As with systematic reviews, a search strategy must be developed before conducting the review.

Integrative Review

An integrative review is less systematic and can be helpful for developing a theoretical model or to reconceptualize a topic. As Synder (2019) notes, " This type of review often re quires a more creative collection of data, as the purpose is usually not to cover all articles ever published on the topic but rather to combine perspectives and insights from di ff erent fi elds or research traditions" (p. 336).

Source: Snyder, H. (2019). Literature review as a research methodology: An overview and guidelines. Journal of Business Research. 104. 333-339. doi: 10.1016/j.jbusres.2019.07.039

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Why do we write literature reviews?

 Literature reviews provide you with a handy guide to a particular topic. If you have limited time to conduct research, literature reviews can give you an overview or act as a stepping stone.

When preparing your grant application, and developing a literature review outside of your discipline.

For professionals, they are useful reports that keep them up to date with what is current in the field.

For scholars, the depth and breadth of the literature review emphasizes the credibility of the writer in his or her field. Literature reviews also provide a solid background for a research paper's investigation.

Comprehensive knowledge of the literature of a discipline or subject

is an essential component of most research assignments.

What is a literature review?

A literature review discusses and analyzes published information in a particular subject area. Sometimes the information covers a certain time period.

A literature review is more than a summary of the sources, it has an organizational pattern that combines both summary and synthesis. A summary is a recap of the important information of the source, but a synthesis is a re-organization, or a reshuffling, of that information. It might give a new interpretation of old material or combine new with old interpretations. Or it might trace the intellectual progression of the field, including major debates. And depending on the situation, the literature review may evaluate the sources and advise the reader on the most pertinent or relevant.

But how is a literature review different from an academic research paper?

While the main focus of an academic research paper is to support your own argument, the focus of a literature review is to summarize and synthesize the arguments and ideas of others. The academic research paper also covers a range of sources, but it is usually a select number of sources, because the emphasis is on the argument. Likewise, a literature review can also have an "argument," but it is not as important as covering a number of sources. In short, an academic research paper and a literature review contain some of the same elements. In fact, many academic research papers will contain a literature review section. What aspect of the study (either the argument or the sources) that is emphasized determines what type of document it is.

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Similarities and Differences of Review of Related Literature and Review of Related Studies 

Back to: Introduction to Educational Research Methodology

Similarities and Differences of Review of Related Literature and Review of Related Studies

Educational research means the organized collection and examination of the data related to education. It is a scientific study that examines the learning and teaching methods for better understanding of the education system. It is an observation and investigation in the field of education. Research is done in search of new knowledge or to use the existing knowledge in a better way. It helps to acquire useful knowledge and solve the challenges faced in education. Research tries to get a better understanding of education.

Literature review means the overview of the works published previously on a subject matter. It is the summary of the work done by other authors on a topic. Literature review will help a researcher in understanding how to carry on the research and what needs to be covered. 

Similarities between Review of Related Literature and Review of Related Studies

i). Both RRL and RRS is done to understand a subject matter extensively. 

ii). Help an individual to understand their topic of interest in-depth. 

iii). To understand what has already been discovered about a topic and what needs to be researched further. 

Differences of Review of Related Literature and Review of Related Studies

i). Related literature is done from books, professional journals, newspapers, magazines, and other publications. Related studies consist of theses, manuscripts, and dissertations. 

ii). After literature review, the individual tries to develop his/her own opinion on the topic. Review of related studies is obtaining answers from what has been studied. 

iii). Related literature focuses on the opinions and ideas of one’s own on a particular topic. Related studies analyze the work of other researchers and focus on the results received by them.  

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CHAPTER 2 REVIEW OF RELATED LITERATURE AND STUDIES

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A systematic review and meta-analysis of pollutants in environmental media

• Chun-Hong Xiao 1 ,
• Xiang-Zhou Meng 2 , 3 , 4 ,
• Ben-Xiang Li 5 &
• Hong-Wen Gao 1  

Environmental Science and Pollution Research volume  30 ,  pages 113205–113217 ( 2023 ) Cite this article

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Environmental pollutants are ubiquitous in our environmental media, resulting in detrimental impacts on both humans and the environment. An evidence-based review, particularly a systematic review and meta-analysis, performs a crucial function in assessing the pollution status of pollutants in environmental media at national and global scales. We selected and thoroughly investigated 76 papers focusing on systematic reviews and meta-analyses of contaminants in environmental media. The need to broaden the scope of studies was observed with an increase in the total number of publications, and there were greater focuses on food safety, water pollution, biological pollution, and environmental risks. Furthermore, this review outlined the fundamental procedures involved in a systematic review and meta-analysis, including literature searching, screening of articles, study quality analysis, data extraction and synthesis, and meta-analysis. A meta-analysis typically comprises fixed- and/or random-effects meta-analysis, identifying and measuring heterogeneity, sensitivity analysis, publication bias, subgroup analysis, and meta-regression. We specifically explored the application of meta-analysis to assess the presence of contaminants in environmental media based on two different pollutant categories, namely, non-biological and biological pollutants. The mean value is commonly utilized to assess the pooled concentration of non-biological pollutants, while the prevalence serves as the effect size of biological pollutants. Additionally, we summarized the innovative applications, frequent misuses, and problems encountered in systematic reviews and meta-analyses. Finally, we proposed several suggestions for future research endeavors.

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Xiao, CH., Meng, XZ., Li, BX. et al. A systematic review and meta-analysis of pollutants in environmental media. Environ Sci Pollut Res 30 , 113205–113217 (2023). https://doi.org/10.1007/s11356-023-30347-5

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Employment of patients with rheumatoid arthritis - a systematic review and meta-analysis

• Lilli Kirkeskov 1 , 2 &
• Katerina Bray 1 , 3  

BMC Rheumatology volume  7 , Article number:  41 ( 2023 ) Cite this article

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Patients with rheumatoid arthritis (RA) have difficulties maintaining employment due to the impact of the disease on their work ability. This review aims to investigate the employment rates at different stages of disease and to identify predictors of employment among individuals with RA.

The study was carried out according to the Preferred Reporting Items for Systematic Reviews and Meta-Analysis (PRISMA) guidelines focusing on studies reporting employment rate in adults with diagnosed RA. The literature review included cross-sectional and cohort studies published in the English language between January 1966 and January 2023 in the PubMed, Embase and Cochrane Library databases. Data encompassing employment rates, study demographics (age, gender, educational level), disease-related parameters (disease activity, disease duration, treatment), occupational factors, and comorbidities were extracted. Quality assessment was performed employing Newcastle–Ottawa Scale. Meta-analysis was conducted to ascertain predictors for employment with odds ratios and confidence intervals, and test for heterogeneity, using chi-square and I 2 -statistics were calculated. This review was registered with PROSPERO (CRD42020189057).

Ninety-one studies, comprising of a total of 101,831 participants, were included in the analyses. The mean age of participants was 51 years and 75.9% were women. Disease duration varied between less than one year to more than 18 years on average. Employment rates were 78.8% (weighted mean, range 45.4–100) at disease onset; 47.0% (range 18.5–100) at study entry, and 40.0% (range 4–88.2) at follow-up. Employment rates showed limited variations across continents and over time. Predictors for sustained employment included younger age, male gender, higher education, low disease activity, shorter disease duration, absence of medical treatment, and the absence of comorbidities.

Notably, only some of the studies in this review met the requirements for high quality studies. Both older and newer studies had methodological deficiencies in the study design, analysis, and results reporting.

Conclusions

The findings in this review highlight the prevalence of low employment rates among patients with RA, which increases with prolonged disease duration and higher disease activity. A comprehensive approach combining clinical and social interventions is imperative, particularly in early stages of the disease, to facilitate sustained employment among this patient cohort.

Peer Review reports

Rheumatoid arthritis (RA) is a chronic, inflammatory joint disease that can lead to joint destruction. RA particularly attacks peripheral joints and joint tissue, gradually resulting in bone erosion, destruction of cartilage, and, ultimately, loss of joint integrity. The prevalence of RA varies globally, ranging from 0.1- 2.0% of the population worldwide [ 1 , 2 ]. RA significantly reduces functional capacity, quality of life, and results in an increase in sick leave, unemployment, and early retirement [ 3 , 4 , 5 ]. The loss of productivity due to RA is substantial [ 2 , 5 , 6 , 7 ]. A 2015 American study estimated the cost of over $250 million annually from RA-related absenteeism in United States alone [ 8 ].

Research has highlighted the importance of maintaining a connection to the labour market [ 3 , 9 ], Even a short cessation from work entails a pronounced risk of enduring work exclusion [ 10 ]. In Denmark merely 55% on sick leave for 13 weeks succeeded in re-joining the workforce within one year. Among those on sick leave for 26 weeks, only 40% returned to work within the same timeframe [ 11 ]. Sustained employment is associated with an improved health-related quality of life [ 12 , 13 ]. Early and aggressive treatment of RA is crucial for importance in achieving remission and a favourable prognosis reducing the impact of the disease [ 2 , 14 , 15 , 16 ]. Therefore, initiating treatment in a timely manner and supporting patients with RA in maintaining their jobs with inclusive and flexible workplaces if needed is critical [ 3 , 17 ].

International studies have indicated, that many patients with RA are not employed [ 18 ]. In 2020, the average employment rate across Organization for Economic Co-operation and Development (OECD) countries was 69% in the general population (15 to 64 years of age), exhibiting variations among countries, ranging from 46–47% in South Africa and India to 85% in Iceland [ 19 ]. Employment rates were lower for individuals with educational levels below upper secondary level compared to those with upper secondary level or higher education [ 19 ]. For individuals suffering with chronic diseases, the employment rates tend to be lower. Prognostic determinants for employment in the context of other chronic diseases encompasses the disease’s severity, employment status prior to getting a chronic disease, and baseline educational level [ 20 , 21 , 22 ]. These somatic and social factors may similarly influence employment status of patients with RA. Several factors, including the type of job (especially physically demanding occupations), support from employers and co-workers, social safety net, and disease factors such as duration and severity, could have an impact on whether patients with RA are employed [ 17 , 23 , 24 ]. Over the years, politicians and social welfare systems have tried to improve the employment rates for patients with chronic diseases. In some countries, rehabilitation clinics have been instrumental in supporting patients to remain in paid work. Healthcare professionals who care for patients with RA occupy a pivotal role in preventing work-related disability and support the patients to remain in work. Consequently, knowledge of the factors that contribute to retention of patients with RA at work is imperative [ 17 , 25 ].

The aim of this study is therefore to conduct a systematic review, with a primary focus on examining employment rates among patients with RA at the onset of the disease, at study entry, and throughout follow-up. Additionally, this study intends to identify predictors of employment. The predefined predictors, informed by the author’s comprehensive understanding of the field and specific to RA, encompass socioeconomic factors such as age, gender, level of education, employment status prior to the disease, disease stage and duration, treatment modalities, and comorbidities, including depression, which are relevant both to RA and other chronic conditions [ 26 ].

This systematic review was carried out according to Preferred Reporting Items for Systematic Reviews and Meta-Analysis (PRISMA) for studies that included employment rate in patients with rheumatoid arthritis [ 27 ]. PROSPERO registration number: CRD42020189057.

Selection criteria and search strategies

A comprehensive literature search was conducted, covering the period from January 1966 to January 2023 across the PubMed, Embase, and Cochrane Library databases using the following search terms: (Rheumatoid arthritis OR RA) AND (employment OR return to work). Only studies featuring a minimum cohort size of thirty patients and articles in the English language were deemed eligible for inclusion.

The initial screening of articles was based on the titles and abstracts. Studies comprising a working-age population, with current or former employment status, and with no limitations to gender, demographics, or ethnicity were included in this review. Articles addressing topics of employment, work ability or disability, return to work or disability pension were encompassed within the scope of this review. Full-time and part-time employment, but not ‘working as housewives’ was included in this review’s definition of employment. Studies involving other inflammatory diseases than RA were excluded. Reference lists in the selected articles were reviewed, and more articles were included if relevant. A review of the reference lists in the initially selected articles was conducted, with additional articles incorporated if they proved relevant to the research objectives. The eligible study designs encompassed cohort studies, case–control studies, and cross-sectional studies. All other study designs, including reviews, case series/case reports, in vitro studies, qualitative studies, and studies based on health economics were systematically excluded from the review.

Data extraction, quality assessment and risk-of-bias

The data extraction from the selected articles included author names, year of publication, study design, date for data collection, employment rate, study population, age, gender, educational level, ethnicity, disease duration, and pharmacological treatment. To ensure comprehensive evaluation of study quality and potential bias, quality assessment was independently assessed by two reviewers (LK and KB) using the Newcastle–Ottawa Scale (NOS) for cross-sectional and cohort studies [ 28 ]. Any disparities in the assessment were resolved by discussion until consensus was reached. For cross-sectional studies the quality assessment included: 1) Selection (maximum 5 points): representativeness of the sample, sample size, non-respondents, ascertainment of the risk factor; 2) Comparability (maximum 2 points); study controls for the most important, and any additional factor; 3) Outcome (maximum 3 points): assessment of outcome, and statistical testing. For cohort studies the assessment included: 1) Selection (maximum 4 points): representativeness of the exposed cohort, selection of the non-exposed cohort, ascertainment of exposure, demonstration that the outcome of interest was not present at start of study; 2) Comparability (maximum 2 points): comparability of cohorts on the basis of the design or analysis; 3) Outcome (maximum 3 points): assessment of outcome, was the follow-up long enough for outcomes to occur, and adequacy of follow up of cohorts. The rating scale was based on 9–10 items dividing the studies into high (7–9/10), moderate (4–6) or low (0–3) quality. A low NOS score (range 0–3) indicated a high risk of bias, and a high NOS score (range 7–9/10) indicated a lower risk of bias.

Analytical approach

For outcomes reported in numerical values or percentages, the odds ratio along with their 95% confidence intervals (CI) were calculated, whenever feasible. Weighted means were calculated, and comparisons between these were conducted using t-test for unpaired data. Furthermore, meta-analysis concerning the pre-determined and potentially pivotal predictors for employment status, both at disease onset, study entry, and follow-up was undertaken. The predictors included age, gender, ethnicity, level of education, duration of disease, treatment, and the presence of comorbities, contingent upon the availability of the adequate data. Additionally, attempts have been made to find information regarding on job categorizations, disease activity (quantified through DAS28; disease activity score for number of swollen joints), and quality of life (SF-36 scores ranging from 0 (worst) to 100 (best)). Age was defined as (< = 50/ > 50 years), gender (male/female), educational level college education or more/no college education), race (Caucasian/not Caucasian), job type (non-manual/manual), comorbidities (not present/present), MTX ever (no/yes), biological treatment ever (no/yes), prednisolone ever (no/yes), disease duration, HAQ score (from 0–3)), joint pain (VAS from 1–10), and DAS28 score. Age, disease duration, HAQ score, VAS score, SF36 and DAS28 were in the studies reported by mean values and standard deviations (SD). Challenges were encountered during attempts to find data which could be used for analysing predictors of employment status before disease onset, and at follow-up, as well as factors related to treatments beyond MTX, prednisolone, and biological as predictors for being employed after disease onset. Test for heterogeneity was done using Chi-squared statistics and I 2 , where I 2 below 40% might not be important; 30–60% may represent moderate heterogeneity; 50–90% substantial heterogeneity; and 75–100% considerable heterogeneity. Meta-analysis for predictors for employment and odds ratio; confidence intervals; and test for heterogeneity were calculated using the software Review Manager (RevMan, version 5.3. Copenhagen: The Nordic Cochrane Centre, The Cochrane Collaboration, 2014).

General description of included studies

The search yielded a total of 2277 references addressing RA its association with employment. Following the initial title screen, 199 studies were considered relevant for further evaluation. Of those, 91 studies ultimately met the inclusion criteria. Figure  1 shows the results of the systematic search strategy.

Flow chart illustrating the systematic search for studies examining employment outcome in patients with rheumatoid arthritis

Table 1 summarizes the general characteristics of the included studies. The publication year of the included studies ranged from 1971 to 2022. Among the studies, 60 (66%) adopted a cross-sectional research design [ 13 , 18 , 29 , 30 , 31 , 32 , 33 , 34 , 35 , 36 , 37 , 38 , 39 , 40 , 41 , 42 , 43 , 44 , 45 , 46 , 47 , 48 , 49 , 50 , 51 , 52 , 53 , 54 , 55 , 56 , 57 , 58 , 59 , 60 , 61 , 62 , 63 , 64 , 65 , 66 , 67 , 68 , 69 , 70 , 71 , 72 , 73 , 74 , 75 , 76 , 77 , 78 , 79 , 80 , 81 , 82 , 83 , 84 , 85 , 86 , 87 , 88 , 129 ] with a total of 41,857 participants analysing data at a specific point in time. Concurrently, 31 studies (34%) adopted a cohort design [ 89 , 90 , 91 , 92 , 93 , 94 , 95 , 96 , 97 , 98 , 99 , 100 , 101 , 102 , 103 , 104 , 105 , 106 , 107 , 108 , 109 , 110 , 111 , 112 , 113 , 114 , 115 , 116 , 117 , 118 , 119 , 120 , 121 , 122 , 130 ] with a total of 59,974 participants. Most of these studies exhibited a small to moderate sample size, with a median of 652 participants. Additionally, single centre studies and studies from high-income countries were predominant. Study details are shown in Table 1 .

General description of study participants

On average, patients with RA were 51 years old, with an age range spanning from 42 to 64 years. Furthermore, the female population accounted for 75.9% of the patient cohort, with a range from 41 to 92%. The duration of the disease at study entry exhibited significant variability, ranging from less than one year up to more than 18 years on average.

• Employment rate

At disease onset, the employment rate was 78.8% (weighted mean, range 45.4–100), at study entry 47.0% (range 18.5–100), and during the follow-up period 40.0% (range 4–88.2), as shown in Table 2 . Notably, a comparative analysis of the employment rates between Europe and North America indicated no substantial difference ( p  = 0.93). However, the comparison between Europe, North America and ‘other continents’ did yield significant differences (or nearly differences) with p -values of 0.003 and 0.08, respectively.

The employment rate exhibited no change, when comparing studies from the 1980s through to 2022. Specifically, the weighted mean for the years 1981–2000 was 49.2%, aligning closely with the corresponding figures for the years 2001–2010 (49.2%) and 2011–2022 43.6%. These findings were statistically non-significant, with p -values of 0.80 for comparison between year 1981–2000 and 2001–2010; 0.66 for 2001–2010 and 2011–2022, and 0.94 for 1981–2000 and 2011–2022, shown in Figure S 1 , see Additional file.

Among the studies included in the analysis, nineteen studies included data of employment at follow-up, with durations ranging from 1 to 20 years, Table 2 . For instance, Jäntti, 1999 [ 97 ] reported an employment rate 69% one year after disease onset, which gradually declined to 50% after 15 years and further to 20% after 20 years. Similarly, Mäkisara, 1982 [ 63 ] demonstrated that 60% of the patients were employed 5 years after disease onset, 50% after 10 years, and 33% after 15 years. Nikiphorou, 2012 [ 101 ] reported an employment rate of 67% at study entry, which decreased to 43% after 10 years.

In addition, seven studies included data of employment rate among patients comparing different medical treatments [ 18 , 44 , 56 , 91 , 105 , 110 , 119 ]. These studies indicated that, on average, 55.0% (weighted mean) of the patients were employed after receiving treatment with MTX, while 42.8% after undergoing treatment with a combination of MTX + Adalimumab (all patients were employed at disease onset in these specific studies).

Predictors for employment

Information of normative comparison data to use for meta-analysis of predictors for employment at study entry was available for age, gender, educational level, race, job type, comorbidities, MTX at any time, biological treatment at any time, prednisolone at any time, disease duration, HAQ score, joint pain (VAS-score), and disease activity (DAS28 score). Predictors for employment at study entry was being younger /age below 50 years, being a male, higher educational level (college or more), non-manual work, having no comorbidities, no medical treatment, short disease duration, and low HAQ score, VAS-score, or DAS28 score. Heterogeneity was small for age, gender, medical treatment, and moderate for educational level, and job type as indicted by the I 2 values, Table  3 , and shown in detail in Figures S 2 , S 3 , S 4 , S 5 , S 6 , S 7 , S 8 , S 9 , S 10 , S 11 , S 12 , S 13 , S 14 , S 15 and S 16 , see Additional file.

Assessment of quality of included studies

All studies were subject to rigorous quality assessment. These assessments resulted in categorisation of either medium quality ( n  = 64; 70%) or high-quality studies ( n  = 27; 30%), with no studies falling into the low-quality category. The quality assessment is shown in Tables  4 and 5 .

Notably, many studies were characterised by several common attributes, including cross-sectional study design, single-centre-settings, relatively small sample sizes, and the reliance on self-reported patient data. When including only the high-quality studies in the analyses, the employment rates at study entry changed from 47% (weighted mean, all studies) to 50% (weighted mean, high quality studies).

Key findings

This systematic review has identified a decline in the employment rate among patients with RA, with a notable decrease from disease onset during the study entry to follow-up, where only half of the patients were employed. These findings corroborate earlier research that indicated a substantial decline in employment rates among patients with RA over time. Notably, previous studies have reported that approximately one third of patients with RA stopped working within 2 to 3 years after disease onset, and more than half was unable to work after 10 to 15 years [ 23 , 63 , 93 , 97 , 101 ]. Only few studies have included data from the general population, comparing the employment rates with the rates for patients with RA [ 89 , 90 ]. Comparisons with the general population further underscored the challenges faced by RA patients, as their employment rates were consistently lower.

Despite changes in medical treatment, social security systems, and societal norms over the past decades, there was no significant improvement in the employment for patients with RA. This pattern aligns with data from the Global Burden of Disease studies, highlighting the persistent need for novel approaches and dedicated efforts to support patients with RA in sustaining employment [ 2 , 123 ]. Recent recommendations from EULAR (European Alliance of Associations for Rheumatology) and ACR (American College of Rheumatology) have emphasized the importance of enabling individuals with rheumatic and musculoskeletal diseases to engage in healthy and sustainable work [ 17 , 124 , 125 ].

While different countries possess different social laws and health care systems for supporting patients with chronic diseases, the variations in the weighted mean of employment rates across countries were relatively minor.

In the meta-analysis, one of the strongest predictors for maintaining employment was younger age at disease onset [ 43 , 51 , 101 , 116 ]. Verstappen, 2004 found that older patients with RA had an increased risk of becoming work disabled, potentially caused by the cumulative effects of long-standing RA, joint damage, and diminished coping mechanisms, compared to younger patients [ 23 ].

More women than men develop RA, however this study showed that a higher proportion of men managed to remain employed compared to women [ 18 , 36 , 42 , 43 , 46 , 62 , 71 , 89 , 101 , 116 ]. Previous studies have shown inconsistent results in this regard. Eberhart, 2007 found that a significantly higher number of men with RA worked even though there was no difference in any disease state between the sexes [ 93 ]. De Roos,1999 showed that work-disabled women were less likely to be well-educated and more likely to be in a nonprofessional occupation than working women. Interestingly, there was no association of these variables among men. Type of work and disease activity may influence work capacity more in women than in men [ 46 ]. Sokka, 2010 demonstrated a lower DAS28 and HAQ-score in men compared to women among the still working patients with RA, which indicated that women continued working at higher disability and disease activity levels compared with men [ 18 ].

Disease duration also played a significant role as a predictor of employment outcomes [ 33 , 36 , 45 , 71 , 77 , 86 , 102 , 111 ]. Longer disease duration correlate with decreased employment likelihood, which could be attributed to older age and increased joint damage and disability in patients with longer-standing RA.

Higher educational levels were associated with a greater possibility of employment [ 30 , 43 , 45 , 46 , 51 , 62 , 86 ]. This is probably due to enhanced job opportunities, flexibility, lower physical workload, better insurance coverage, and improved health care for well-educated individuals. This is further supported by the fact that having a manual work was a predictor for not being employed [ 30 , 39 , 43 , 44 , 45 ].

Furthermore, health-related quality of life, as measured by SF 36, lower disease activity (DAS28 scores), reduced joint pain (VAS-score), and lower disability (HAQ score) were additionally predictors for being employed [ 33 , 35 , 36 , 45 , 71 , 86 ]. This support the statement that the fewer symptoms from RA, the greater the possibility of being able to work.

The results showed that the presence of comorbidity was a predictor for not being employed, aligning with findings from previous studies that chronic diseases such as cardiovascular disease, lung disease, diabetes, cancer, and depression reduced the chances of being employed [ 126 ]. Moreover, the risk of exiting paid work increased with multimorbidity [ 127 ].

While limited data were available for assessing the impact of treatment on employment, indications suggested that patients with RA were receiving medical treatments, such as MTX or biological medicine, were more likely to be unemployed. One possible explanation for this phenomenon could be that patients with RA, who were receiving medical treatment, had a more severe and a longer duration of RA compared to those, who had never been on medical treatment. However, the scarcity of relevant studies necessitates caution when drawing definitive conclusions in this regard.

Therefore, the predictors for employment found in this review were being younger, being a male, having higher education, low disease activity, low disease duration, and being without comorbidities. This is supported by previous studies [ 93 , 116 ]

In summary, this review underscores the importance of managing disease activity, offering early support to patients upon diagnosis, and reducing physically demanding work to maintain employment among patients with RA. Achieving success in this endeavour requires close cooperation among healthcare professionals, rehabilitation institutions, companies, and employers. Furthermore, it is important that these efforts are underpinned by robust social policies that ensure favourable working conditions and provide financial support for individuals with physical disabilities, enabling them to remain active in the labour market.

Strengths and limitations

The strength of this review and meta-analysis lies in the inclusion of a large number of articles originating from various countries. Furthermore, the data showed a consistent employment rate in high quality studies compared to all studies. However, there are some limitations to this review. No librarian was used to define search terms and only three databases were searched. Furthermore, the initial search, selection of articles, data extraction, and analysis was undertaken only by one author, potentially leading to the omission of relevant literature and data. The review also extended back to 1966, with some articles from the 1970s and 1980s included. Given the significant changes in medical treatment, social security systems, and society over the past decades, the generalizability of the findings may be limited.

Moreover, the majority of studies did not include a control group from the general population, which limited the ability to compare employment rates with the general population in the respective countries. Many studies were cross-sectional in design, which limits the evidence of causality between employment rate and having RA. However, the employment rate was approximately the same in high quality studies compared to all studies, which supports an association. A substantial number of studies relied on self-reported employment rates, introducing the potential for recall bias. Additionally, many studies did not account for all relevant risk factors for unemployment failing to control for all relevant confounders.

EULAR have made recommendation for point to consider when designing, analysing, and reporting of studies with work participation as an outcome domain in patients with inflammatory arthritis. These recommendations include study design, study duration, and the choice of work participation outcome domains (e.g., job type, social security system) and measurement instruments, the power to detect meaningful effects, interdependence among different work participation outcome domains (e.g., between absenteeism and presentism), the populations included in the analysis of each work participation outcome domain and relevant characteristics should be described. In longitudinal studies work-status should be regularly assessed and changes reported, and both aggregated results and proportions of predefined meaningful categories should be considered [ 128 ]. Only some of the studies in this review met the requirements for high quality studies. In both older and newer studies methodological deficiencies persisted in study design, analysis, and reporting of results, as recommended by EULAR.

Perspectives for future studies

Future research in this area should focus on developing and evaluating new strategies to address the ongoing challenges faced by patients with RA in maintaining employment. Despite many initiatives over the years, there has been no success in increasing employment rates for patients with RA in many countries. Therefore, there is a pressing need for controlled studies that investigated the effectiveness of interventions such as education, social support, and workplace adaptations in improving employment outcomes for these individuals.

This systematic review underscores the low employment rate among patients with RA. Key predictors of sustained employment include being younger, having higher educational level, short disease duration, and lower disease activity, along with fewer comorbidities. Importantly, the review reveals that the employment rate has not changed significantly across different time periods. To support patients with RA in maintaining their employment, a comprehensive approach that combines early clinical treatment with social support is crucial. This approach can play a pivotal role in helping patients with RA stay connected to the labour market.

Availability of data and materials

The datasets used and/or analyzed during the current study are available in the supplementary file.

Abbreviations

• Rheumatoid arthritis

Methotrexate

Newcastle Ottawa Quality Assessment Scale

Standard deviation

Not analyzed

Not relevant

Disease activity

Health Assessment Questionnaire

Visual analog scale for pain

European Alliance of Associations for Rheumatology

American College of Rheumatology

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Lilli Kirkeskov & Katerina Bray

Department of Social Medicine, University Hospital Bispebjerg-Frederiksberg, Nordre Fasanvej 57, Vej 8, Opgang 2.2., 2000, Frederiksberg, Denmark

Lilli Kirkeskov

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LK performed the systematic research, including reading articles, performed the blinded quality assessment and the meta-analysis, and drafted and revised the article. KM performed the blinded quality assessment and the discussion afterwards of articles to be included in the research and the scores, and drafted and revised the article.

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Supplementary Information

Additional file 1: figure s1..

Employment; year of investigation.

Additional file 2: Figure S2.

Forest Plot of Comparison: Predictors for employment. Outcome: Younger or older age.

Additional file 3: Figure S3.

Forest Plot of Comparison: Predictors for employment. Outcome: >50 yr or <50 yr of age.

Additional file 4: Figure S4.

Forest Plot of Comparison: Predictors for employment. Outcome: Gender: Male or Female.

Additional file 5: Figure S5.

Forest Plot of Comparison: Predictors for employment. Outcome: Educational level: no college education or college education or higher.

Additional file 6: Figure S6.

Forest Plot of Comparison: Predictors for employment. Outcome: no comorbidities present or one or more comorbidities present.

Additional file 7: Figure S7.

Forest Plot of Comparison: Predictors for employment. Outcome: Ethnicity: Caucasian or other than Caucasian.

Additional file 8: Figure S8.

Forest Plot of Comparison: Predictors for employment. Outcome: Short or long disease duration.

Additional file 9: Figure S9.

Forest Plot of Comparison: Predictors for employment. Outcome: Low or high Health Assessment Questionnaire, HAQ-score.

Additional file 10: Figure S10.

Forest Plot of Comparison: Predictors for employment. Outcome: Low or high VAS-score.

Additional file 11: Figure S11.

Forest Plot of Comparison: Predictors for employment. Outcome: Job type: blue collar workers or other job types.

Additional file 12: Figure S12.

Forest Plot of Comparison: Predictors for employment. Outcome: No MTX or MTX.

Additional file 13: Figure S13.

Forest Plot of Comparison: Predictors for employment. Outcome: No biological or biological.

Additional file 14: Figure S14.

Forest Plot of Comparison: Predictors for employment. Outcome: No prednisolone or prednisolone.

Additional file 15: Figure S15.

Forest Plot of Comparison: Predictors for employment. Outcome: Low or high DAS score.

Additional file 16: Figure S16.

Forest Plot of Comparison: Predictors for employment. Outcome: Low or high SF 36-score.

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Kirkeskov, L., Bray, K. Employment of patients with rheumatoid arthritis - a systematic review and meta-analysis. BMC Rheumatol 7 , 41 (2023). https://doi.org/10.1186/s41927-023-00365-4

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Review article, a scoping review of music-based interventions for swallowing difficulties: implications for treating older adults with presbyphagia.

• 1 Music Therapy Education, Graduate School of Education, Ewha Womans University, Seoul, Republic of Korea
• 2 Department of Music Therapy, Graduate School, Ewha Womans University, Seoul, Republic of Korea

Objectives: Presbyphagia refers to age-related changes in the swallowing mechanism (e.g., reduced skeletal muscle strength that decreases bolus control). If left untreated, these changes can lead to dysphagia, which refers to impaired swallowing (e.g., coughing or choking when eating). Given that swallowing difficulties are common among older adults that they make up the fastest growing age group globally, the need for interventions to address presbyphagia is gaining urgency. To begin to address this need, we conducted a scoping review to analyze music therapy research aimed at enhancing swallowing function. The objective was to identify key intervention characteristics and propose clinical implications for treating presbyphagia using music therapy.

Methods: This review followed the methodological frameworks outlined by Arksey and O’Malley and Levac et al. and used the Preferred Reporting Items for Systematic Reviews and Meta-Analysis for Scoping Reviews for analysis and reporting. Four electronic databases (i.e., ProQuest, PubMed, RISS, Web of Science) were searched for quantitative and qualitative studies in English or Korean that used music-based interventions to address swallowing function in older adults. Content analysis was conducted to identify and compare the main features of music interventions for swallowing difficulties among older adults.

Results: Ten articles were identified and analyzed. It was found that three core components–respiration, vocalization, and singing–were employed to enhance swallowing function in populations with neurological impairments, dementia, or head and neck cancer. Notably, actions closely linked to swallowing function, such as laryngeal elevation and oral movements, were utilized therapeutically to speak or sing. Based on these characteristics, clinical implications are proposed to address presbyphagia.

Conclusion: Singing entails a systematic and focused incorporation of stepwise activities that can be used to address swallowing disorders. In this context, critical clinical implications that music therapists should consider when treating individuals with presbyphagia include warmup breathing, vocalizing targeting laryngeal control, and singing targeting oral motor control. This review can contribute to the expansion of music therapy with older adults and the advancement of music therapy techniques.

1. Introduction

The global population of individuals aged 65 years or older currently stands at 720 million, with projections indicating a doubling of this figure within the next three decades ( 1 ). Among older adults, a prominent characteristic is the gradual decline in multiple physical functions, rendering them more vulnerable to conditions such as sarcopenia, dysphagia, osteoporosis, and frailty ( 2 , 3 ). Given the rise in life expectancy and the multifaceted nature of aging, encompassing biological, psychological, and social changes, it is imperative we gain a deeper comprehension of how to effectively treat common age-related difficulties and disorders. One such difficulty is presbyphagia.

Aging leads to various changes in swallowing physiology, and these changes are collectively referred to as presbyphagia ( 4 ). While presbyphagia refers to normal age-related changes in the swallowing mechanism, these changes may be manageable if treated before they cause difficulties or serious dysfunction in swallowing. Difficulty swallowing is referred to by the umbrella term dysphagia and can be caused by neurological impairment, structural abnormalities, or muscle or brain disorders. Dysphagia has been found to affect over 20% of individuals over the age of 50 years in community settings and nearly 60% of individuals over the age of 80 years in nursing home settings ( 5 ).

Swallowing difficulties encompass both physiological and functional aspects, impacting not only psychological and social wellbeing but also overall health and communication ( 6 , 7 ). As such, difficulties in swallowing can impact an individual’s quality of life. Notably, depression emerges as a significant symptom in this context, drawing attention in several studies ( 8 , 9 ). These studies underscore a substantial link between swallowing difficulties and depression, especially among older adults. This emphasizes the significance of integrating psychological interventions with therapeutic approaches to effectively manage swallowing difficulties.

Swallowing is a neuroanatomical process composed of three stages: oral, oropharyngeal, and esophageal ( 10 , 11 ). Specific structures such as muscles, nerves, the tongue, salivary glands, epiglottis, vocal cords, larynx, and hyoid bone are involved in each stage ( 11 ). Difficulties can arise from either mechanical obstruction or impaired motor function along the pathway through which food and liquid travel. Swallowing difficulties arising from neurological or structural causes necessitate rehabilitation interventions focused on precise motor timing and repetitive tasks to enhance function ( 12 , 13 ). Interventions addressing swallowing difficulties aim to enhance laryngeal elevation and strengthen the associated muscles, ultimately improving swallowing function in dysphagic patients ( 14 , 15 ).

The age-related changes defining of presbyphagia, such as diminished tongue pressure from muscle loss and extended upper esophageal sphincter opening times, increase an individual’s risk for dysphagia, including increased risk of aspiration ( 16 ). Unfortunately, conventional swallowing treatment modalities such as supraglottic swallow and Medelsohn maneuver, may be inappropriate or less effective with older populations ( 17 ). For instance, older adults commonly experience heightened fatigue and comorbidities that prohibit them from adhering the treatment. Therefore, when addressing swallowing changes and difficulties in older adults, it is crucial to consider the specific needs and limitations of this population, including the use of proper sensory activation and easily manageable swallowing motor tasks.

As an alternative to conventional treatment modalities, music-based interventions can target the oral and vocal structures involved in the process of swallowing and can be designed to meet the unique needs of older patients. In particular, singing can directly induce functional changes ( 18 , 19 ). The basis for applying singing to improve swallowing function stems from respiration, phonation, and articulation sharing common neuroanatomical processes. Specifically, singing activates an auditory-motor feedback loop in the brain, which is further strengthened by the common neural network shared between singing and speaking ( 20 ). The processes of swallowing and vocalization are intricate coordination systems that necessitate precise integration of musculature in the upper airway, encompassing the oral, pharyngeal, laryngeal, and respiratory regions ( 21 ). Because singing requires coordination of respiration, vocalization, and articulation ( 22 – 24 ), it can address the needs of patients with dysphagia by integrating musical elements such as melody and rhythm. Thus, perceiving vocal melodies and integrating vocal and auditory information in speech production during singing involve neural engagement in auditory, linguistic, and emotional processing ( 25 ). The use of singing as a therapeutic method has been proven effective in the rehabilitation of diverse medical conditions, including stroke, aphasia, and mood disorders ( 26 ).

Singing has emerged as a promising rehabilitative approach in the realm of swallowing treatment, as evidenced by studies in neurorehabilitation ( 27 , 28 ). While these singing-based music therapy approaches for dysphagia hold promise, the majority of the literature focuses on speech function ( 29 , 30 ). It has been discovered that laryngeal elevation-based techniques applied in singing demonstrate favorable outcomes for patients with neurological impairment. The utilization of singing as a rehabilitative approach for improving swallowing function can be rationalized based on the evidence that the mechanisms involved in singing, including breathing, vocalization, and articulation ( 31 ), also play a crucial role in the process of swallowing.

Considering the need to expand the applications of music-based interventions, it is important to understand the theoretical and clinical characteristics of music-based intervention tasks. To address this need, we conducted a scoping review of music-based interventions focused on improving swallowing function. Scoping reviews use structured guidelines to synthesize information ( 32 ). This scoping review sought to gain insight from the research exploring the role of music-based interventions in swallowing rehabilitation and determine if there was consensus regarding the therapeutic components used to improve particular functional outcomes. Based on the analysis of the research, we suggest clinical implications for music therapists working with individuals with presbyphagia.

Levac et al. ( 33 ) refined the stepwise process originally outlined by Arksey and O’Malley ( 34 ) for scoping literature reviews, and we followed Levac et al.’s five stages, with the literature search and selection process being conducted iteratively. Additionally the research process, if there were areas that needed further supplementation based on data collection and review, continuous modifications were made to the process. In this study, we used the population, concept, context (PCC) framework to enhance the validity of the research presented in the JBI reviewer’s manual and other guidelines ( 35 , 36 ). The framework’s detailed standards for classifying and analyzing information are the following;

2.1. identifying the research question(s)

The scope of the research on this topic is extensive, so questions regarding the research should use precise descriptions and specific inclusion criteria ( 33 , 37 ). In other words, research questions must be defined clearly with criteria, as they provide a roadmap for subsequent stages, including research subjects, interventions, and outcomes. Therefore, this study constructed research questions considering the PCC framework. The PCC framework was used to establish the following:

• Population: Adults who experienced swallowing difficulties or swallowing disorders.

• Concept: The use of music-based interventions to treat swallowing difficulties/disorders among adults.

• Context: Publications describing music-based interventions for swallowing issues as a primary concern, written in either Korean or English.

Based on the PCC framework described above, the research questions for this study were as follows:

• What types of music-based intervention studies have been conducted to date that have addressed swallowing function in adults?

• What are the components of music-based interventions to improve swallowing function among adults?

• Given the components of music-based interventions for improving swallowing function, what are the clinical implictions for treating individuals with presbyphagia?

2.2. Searching the literature

A two-step search method was employed using electronic databases to conduct a literature search for published research. This method involved an initial search followed by reference and related literature searching. The procedures for selecting the database and keywords for the initial search were as follows.

2.2.1. Selection of databases

Given the need for expertise and objectivity in music therapy interventions, we only reviewed published work from academic research databases. Conducting a literature review within the scope of the present topic requires collecting a substantial number of research findings. It takes time to comprehensively gather research results through keyword searches, especially for topics in which non-standardized terms are used interchangeably, such as in music therapy. In addition, the authors communicated with experienced researchers in the field of literature reviews and systematic literature analysis to ensure databases that offered advanced search capabilities and were commonly used for literature reviews were selected. Consequently, ProQuest, PubMed, Research Information Sharing Service, and Web of Science databases were used with no date restriction.

2.2.2. Selection of search terms

The literature regarding music-based interventions for improving swallowing function was identified and analyzed. Music-based interventions use music to achieve therapeutic goals and may be implemented by music therapists or other professionals ( 38 ). Keywords commonly used in the field were supplemented with subject terms that aligned with the objectives of the study. To ensure a comprehensive search was conducted, the researchers modified the search terms and the sequence of database usage, repeating the search on different days to compare results. MeSH terms related to diagnoses (e.g., “swallowing disorder”) and musical techniques (e.g., “music,” “singing,” “vocal”) were combined with “intervention” and “therapy.” In addition, intervention-related terms such as “treatment,” “rehabilitation,” “training,” and “intervention” were employed, either individually or within specific categories in English and Korean. Research that was published in Korean was translated into English. The validity of the translation was verified through mutual discussion among the researchers. Table 1 shows the databases and search strategies used.

Table 1 . Databases and search strategies using keywords.

2.3. Stage 3: identifying studies

Inclusion criteria were the following: (a) implementation of a music-based intervention targeting swallowing function, (b) publication in English or Korean, and (c) reporting of measurable functional changes of swallowing or laryngeal diadochokinesis as a secondary assessment indicator of swallowing function. Exclusion criteria were (a) participants under 20 years of age, (b) duplicate intervention with the same participants, and (c) music listening intervention only. To remove duplicates and irrelevant articles, two researchers (SKi and SKa) screened article abstracts based on the previously described search strategy. Then the two other researchers (SJK and MY) revalidated the identified articles.

The assessment of study eligibility during the initial full-text screening involved two researchers (SJK and MY). Subsequently, to ensure the inclusion of studies aligned with the review’s objectives, the researchers conducted multiple rounds of full-text reviews. Instances of disagreement were resolved through consensus achieved during meetings and discussions. Final selection of articles was based on consensus.

2.4. Charting the data

The data retrieval and organization were done using EndNote X9 software from Clarivate Analytics (PA, USA). Then, to code the data, our framework was established in advance. Our framework includes general study information and details about the research questions. The charting table was completed independently by one researcher (MY) and peer reviewed by two researchers (SJK and SKi). A data extraction template was created to organize information from the identified articles. To ensure comprehensive data coverage, the researchers conducted the literature collection and selection processes twice, altering the order of the databases and sequence of the search terms.

To finalize the literature search, we used a modified data extraction form developed by JBI researchers ( 39 ). Two authors independently reviewed and cross-checked each selected literature and coded the data using Microsoft Excel 2022. The extracted data involved author name(s), publication year, country where the research was conducted, research methodology, participant population, intervention activities and their specific elements, reported outcomes, effects of the intervention, and details about the musical tasks used. We also categorized the intervention content described in each study by specific activity and analyzed the results to compare commonalities and differences across the studies. In addition, data collected about the music therapy interventions included intervention provider, intervention contents, intensity of sessions, presence of protocol groundwork, composition of musical tasks, and therapeutic rationale. Similar activities were grouped under the same category and classified accordingly.

The collected data was categorized and analyzed following the charting table’s detailed criteria (see Table 2 ).

Table 2 . Charting framework’s detailed criteria.

2.5. Collating, summarizing, and reporting the results

This stage of the scoping review was informed by the methodological framework outlined by Levac et al. ( 33 ). A comprehensive descriptive synthesis of the data presented in the charting table was conducted by three researchers (SJK, MY, SKi), while qualitative content analysis techniques were applied by two reviewers (SJK, MY) to formulate clinical strategies for addressing presbyphagia. The results from the synthesis and qualitative analysis were subsequently used to contextualize the results, specifically in relation to our research questions, and to inform the clinical implications surrounding the integration of music therapy sessions for individuals with presbyphagia. These insights also point to future research directions.

The search process identified 105 studies from the target databases. After duplicates were removed, 72 citations underwent title and abstract screenings. Following this 62 studies were excluded because they did not meet the inclusion criteria. Consequently, 10 studies were analyzed for this scoping review (see Figure 1 ).

Figure 1 . Workflow of the scoping review.

3.1. What types of music-based intervention studies have been conducted to date that have addressed swallowing function in adults?

What types of music-based intervention studies have been conducted to date that have addressed swallowing function in adults?

3.1.1. Study characteristics

Of the 10 studies included for analysis, two were published in 2010 ( 27 , 40 ), five between 2012 and 2018 ( 28 , 41 – 44 ), two in 2021 ( 45 , 46 ), and one in 2022 ( 47 ). In terms of research design, there were three case studies ( 28 , 41 , 46 ), two randomized controlled studies ( 42 , 45 ), four one-group pre/post studies ( 27 , 40 , 43 , 44 ), and one ABA-mixed method case series study ( 47 ). The studies were conducted in Korea ( 6 ), USA ( 2 ), Japan ( 1 ), and Russia ( 1 ) ( Table 3 ).

Table 3 . Study characteristics ( N  = 10).

To reiterate, a diagnosis of a swallowing disorder was not required for inclusion in this review. Presbyphagia symptoms can occur without meeting the criteria for dysphagia. It was hoped that by identifying and analyzing music-based interventions focused more generally on swallowing difficulties in adults that insight into the treatment of presbyphagia could be obtained. Among the 10 studies, four applied singing interventions to improve swallowing disorders due to neurological impairments. One study included older adult participants without swallowing disorders ( 42 ) and another included older adult participants at-risk for dysphagia. Singing interventions were also applied to swallowing disorders due to head and neck cancer (HNC) ( 45 ). Two studies included mixed diagnoses with participants diagnosed with either cancer and brain damage ( 46 ) or stroke and dementia ( 40 ). It is important to note that the location of a tumor can impair swallowing as can radiation from cancer treatments. Brain damage from stroke or dementia can also interfere with one’s ability to swallow.

The number of participants who completed the intervention in each study varied from 1 to 29. In one of the three case studies, a single participant was involved ( 41 ), while the other two case studies each had three participants ( 27 , 46 ). The ages of the participants in all 10 studies exceeded 50 years; three studies included participants aged 60 and above ( 43 , 44 , 46 ), and two studies had an average participant age of over 80 years ( 41 , 42 ). Of the 10 studies reviewed, six studies employed individual intervention ( 27 , 28 , 41 , 44 – 46 ), whereas four studies utilized group intervention ( 40 , 42 – 44 ). In terms of conducing sessions, seven studies involved music therapists ( 27 , 28 , 41 – 43 , 46 , 47 ), while three did not report facilitators ( 40 , 41 , 44 ).

Regarding outcome measurements, vocal components, articulation, and swallowing functions were measured. Vocal aspects included measures like maximum phonation time (MPT) and vocal quality (jitter, shimmer, Noise-harmonics to ratio, NHR), while articulation involved tasks such as alternating motion rate (AMR) and sequential motion rate (SMR). For swallowing, direct measures like video fluoroscopic swallowing study (VFSS), video fluoroscopic dysphagia scale (VDS), Dynamic Imaging Grade of Swallowing Toxicity (DIGEST), modified water swallowing test, and mean swallowing pressure were utilized. Indirect methods encompassed assessments within the Frenchay dysarthria assessment related to swallowing functions, laryngeal diadochokinesis (L-DDK) test related to laryngeal-muscle movement, and electromyography (EMG), among others. Only three studies used the Swallowing Quality of Life (SWAL-QoL) questionnaire ( 28 , 43 , 46 ).

3.2. What are the components of music-based interventions to improve swallowing function among adults?

3.2.1. music intervention component analysis.

Within the scope of the scrutinized literature, the therapeutic applications were grounded in singing, commonly employed for speech rehabilitation. As an extended and modified use of the speech production system, singing can be a key element of swallowing interventions in music therapy ( 48 , 49 ). Upon examining the interventions used in each study, they generally applied musical components to focus on swallowing functions in the process of singing, encompassing the respiratory, vocalization, and articulatory stages. To identify the core components of music-based interventions targeting swallowing function, we reviewed not only the intervention contents but also all relevant description details within the studies as well as key reference materials.

The constituent activities within the structured music interventions were subjected to analysis (see Table 4 ). Examining the studies based on the executed activities, it became apparent that the predominant tasks were ‘upper body movement – stretching arms, neck, and shoulders to relax the muscles ( 28 , 41 – 44 , 46 , 47 ), and ‘vocal sound gliding using a vowel sound’ ( 27 , 28 , 42 – 47 ), which was reported in 8 studies among 10 studies. Conversely, activities involving direct stimulation of the laryngeal muscles, pertinent to swallowing, were featured in only four studies ( 27 , 28 , 45 , 46 ). The music tasks related to laryngeal movements closely involved in the swallowing process and airway protection were identified as ‘stepwise breathing’ ( 27 ) and ‘vocalizing (/ah/)-/oo/-/ee/ in ascending pitch order’ ( 27 , 28 , 45 , 46 ). In addition to these, activities related to vocal musculature and orofacial motor skills included humming ( 27 , 28 , 41 , 45 , 46 ) and sound gliding ( 27 , 28 , 42 – 47 ), as well as vocalizing the vowel /a/ while exhaling after inhaling sufficiently ( 46 , 47 ).

Table 4 . Analysis of intervention activities based on goals, target function, approach, studies, and population.

Upon conducting a detailed analysis of each activity in accordance with the therapeutic goals for swallowing function, the following results were obtained. Relaxing of respiratory muscles ( n  = 2) was attempted in a form of diaphragmatic breathing and upper body stretching. Enhancing targeted articulatory system ( n  = 1), and inducing laryngeal muscle movement ( n  = 1) were attempted in a form of singing, while relaxing vocal musculature ( n  = 3) was achieved through activities such as vocal sound gliding, vocalizing vowel sounds, or humming. Activities that directly stimulate the larynx, which plays the most direct role in the swallowing process, include inducing airway protection ( n  = 1), elevating the larynx ( n  = 1), regulating orofacial musculature ( n  = 1), and stimulating orofacial motor skills ( n  = 1).

3.2.2. Vocalization and singing for swallowing

Vocalization activities were undertaken in nine of the studies with diverse objectives and methods. The objectives of these vocalization activities encompassed soft palate elevation, vocal cord relaxation, and laryngeal elevation. In terms of methods, five studies ( 27 , 28 , 45 – 47 ) employed vocalization in the form of glissando or humming to facilitate vocal cord relaxation. These vocalization activities were subdivided into preparatory and execution stages. The preparatory stage of vocal activities typically involves comfortably and lengthily producing the vocalizing vowel /a/ or humming, while the execution stage corresponds to actively controlling vocal structures’ movements to produce sounds with varying pitch while singing.

Regarding intervention activities, several methods were utilized. These included brief glissando utterances by the participant, subsequently reflected upon by the therapist ( 27 , 28 , 45 , 46 ), as well as modeling ( 42 ). Additionally, three studies incorporated aspects of adjusting pitch or tempo given by music therapist ( 27 , 28 , 45 ). Beyond the vocal preparation phase, the primary objectives extended to sustaining laryngeal elevation, enhancing voice intensity, and strengthening motor function in the oral muscles. Furthermore, the introduction of vocal training through diverse methods, including vocal instruction, glissando, and messa di voce (a vocal method that involves maintaining a consistent pitch while gradually increasing the volume of the voice), highlighted the goals and techniques that were utilized.

All studies incorporated a singing phase as part of their intervention. Preferred song singing was performed in two studies ( 28 , 43 ), and in seven studies singing was carried out while modifying respiration or lyrics ( 27 , 41 , 42 , 44 – 47 ). Only one study ( 40 ) included preferred song singing without specific therapeutic goals and described this as a rhythmic activity.

3.2.3. Use of lyrics to focus on targeted oral motor movement

Among the studies involving singing with lyrics, five used singing to improve physical functions such as breathing and articulation ( 28 , 41 , 44 – 46 ). Activities using vocalization of vowels and consonants or singing with lyrics to strengthen the orofacial muscles were presented in all studies. Singing was performed by inserting consonants instead of lyrics. In a study with the primary goal of strengthening oral muscles, a detailed description of the spherical shape of vowels and rationale for the selection criteria of consonants to replace lyrics were presented. It was reported that vocalization using vowels induces various movements of the jaw and helps to strengthen the muscles of the lips, cheeks, and jaw. Also, Korean palatal sounds, such as /gah/ and /kah/, and Korean tongue consonants, such as /tah/, were used to maximize tongue movement.

The manner in which singing was conducted also exhibited variations depending on the type of intervention. In certain cases, singing activities within group interventions were intertwined with functions like articulation and breathing ( 43 , 44 ), while in others, they pertained to speech function ( 28 , 41 – 43 , 45 – 47 ). Notably, these activities pursued goals not directly aligned with swallowing function. Additionally, interventions targeting swallowing function, both in individual and group settings, predominantly comprised breathing and vocalization exercises, as opposed to conventional singing.

3.2.4. Enhanced musical experience

Regarding the use of music, six studies meticulously outlined the therapist’s accompaniment choices ( 27 , 28 , 43 , 45 – 47 ) For instance, during breathing exercises, a trill accompaniment was introduced to signal breath holding during breathing activity or adjustment was made to accommodate the participant’s vocal range and voice intensity during singing. The music excerpt selected for the patient’s involvement was tailored according to the patient’s vocalization.

In contrast, the remaining four studies ( 40 – 42 , 44 ) did not delve into the therapist’s musical involvement, as they refrained from specifying the musical excerpt employed by the therapist or the music incorporated. Instead, their focus rested on monitoring the activity’s progression. The singing process appeared to be centered around general singing without specific musical modifications for a particular purpose. However, the therapist’s musical proficiency emerged as a pivotal factor, as it served as an effective strategy for enhancing engagement and refining participant performance.

When considering vocalizations, the incorporation of musical components into singing activities stands out as crucial, employing an array of approaches. The therapist’s musical expertise assumes a central role in shaping this process, adjusting song composition through alterations in accompaniment and the integration of musical elements. While prioritizing singing activities that accentuate articulation, the prevalent approach involved the direct rendition of familiar songs devoid of a therapeutic rationale.

3.3. Research question 3: given the components of music-based interventions for improving swallowing function, what are the clinical implications for treating individuals with presbyphagia?

3.3.1. clinical implications of singing to treat presbyphagia.

Given the results of this scoping review, we offer clinical implications for music therapy addressing age-related swallowing difficulties in older adults. Singing has clinical viability because it is not sensitive to the patient’s level of cognitive functioning. Considering the attributes of the aging demographic, the co-occurrence of cognitive deterioration is anticipated, thereby amplifying the clinical strength of singing as an intervention that holds significant accessibility for this specific cohort.

In addition, music therapy interventions for presbyphagia should place significant emphasis on respiration, vocalization, and singing. These facets involve extensive engagement and straightforward implementation for a broad segment of the older adult population. To effectively address presbyphagia, these music therapy elements should align with physical activity and target muscle strengthening pertinent to swallowing. Patients should be able to execute these tasks independently to maintain a consistent level of intervention intensity and experience the psychological benefits of music-related activity ( 49 , 50 ).

In interventions incorporating singing, respiratory exercises conducted at the initial stage were predominantly employed alongside relaxing music to elevate activity levels or stretch associated muscles. However, when designing interventions that target swallowing function, particularly tailored for older adults, controlled respiratory exercises are essential, encompassing stronger dynamics and brief breath pauses for practicing the complete closure of the epiglottis, a structure related to swallowing. Hence, there is a need to cautiously incorporate sufficient repetition of regulated respiratory maneuvers.

Vocalization is a vital function closely tied to swallowing, with crucial laryngeal muscle control. Vocal folds, false vocal folds, and aryepiglottic folds contract in tandem with hyoid and laryngeal elevation, protecting the airway ( 51 ). Furthermore, oral control and lingual control are integral to vocalization and swallowing. Both non-speech vocalization and speech demand mouth opening and an upright head position for effective sound projection. Speech adds the complexity of coordinating lip, jaw, and tongue movements; shaping oral-pharyngeal cavities for vowel resonances; and forming obstructions for consonants, requiring synchronization with voice onset and offset ( 52 ).

Considering the relationship between vocalization and swallowing ( 53 ), it becomes apparent from the current research analysis that activities such as humming, vowel sound production, gliding vowel sounds, and vocalizing at different pitches have tended to center around the oral phase. In light of the age-related decline in muscle function among older individuals, movements necessitating resistance, such as laryngeal elevation, should be more proactively integrated. To this end, a diverse array of singing such as vocalizing or singing melodies with various pitch intervals can be effectively employed. Furthermore, avenues for facilitating more vigorous movements of structures like the tongue and jaw need to be explored in vocalization. In singing, careful consideration must be given to the choice of lyrics for vocalization exercises, specifically utilizing lyrics containing certain pronunciations and incorporating direct tongue protrusion and yawning. The overall clinical implications are summarized in Figure 2 .

Figure 2 . Proposed clinical implications based on research analysis.

4. Discussion

The purpose of this article was to analyze relevant research to present the theoretical frameworks and intervention protocols using music-based interventions for swallowing difficulties in adults within rehabilitation settings. Considering the growing need to address swallowing difficulties among older adults, it is necessary to expand the scope of music therapy interventions by looking at the clinical applications of previous research findings. As such, this review synthesized the music therapy applications for swallowing interventions and analyzed components of musical tasks tailored to facilitate swallowing function. Not surprisingly, the majority of studies examined in this review included singing tasks encompassing various target subtasks, such as orofacial muscle exercises and vocalizations, which could be implemented by older adult populations.

Compared to a previous scoping review of singing-centered interventions in pulmonary rehabilitation, the current analysis showed that singing interventions for functional improvement were structured to include respiration, vocalization, and singing. Studies exploring singing in respiratory rehabilitation tend to prioritize community-based group singing, so there was less specific information regarding the therapeutic aspects of singing tasks for functional improvement ( 54 ). It implies that understanding therapeutic considerations in composing music therapy tasks for target behaviors is essential. This aligns with our findings, showing a consistent intervention structure. However, our review found specific vocal and singing tasks associated with swallowing function, suggesting a deliberate inclusion of aspects related to swallowing function.

Among the examined studies, seven ( 27 , 28 , 41 , 42 , 45 – 47 ) evaluated the relationship between oral and language functions in swallowing capabilities. Singing tasks are inherently tied to respiratory control, articulation, and phonation, all of which prominently impact structures involved in swallowing function. Changes observed in these parameters underscore the potential of a singing-based enhancement protocol to exert a comprehensive influence on individuals with presbyphagia. Studies that assessed alterations in laryngeal AMR and L-DDK before and after interventions consistently found proof that musical interventions possess the capacity to concurrently enhance both swallowing and speech functions ( 28 , 45 , 46 ). Furthermore, activities promoting movements of the jawbone or tongue, pivotal for precise articulation, share commonalities with the mechanisms inherent in singing, wherein the lyrical content is structured. Consequently, if forthcoming endeavors integrate singing activities focused on enhancing articulatory engagement, a mutual advancement in both the participants’ swallowing and speech functions could be reasonably anticipated.

In music therapy sessions, selecting and modifying lyrics tailored to each patient are significant tasks for music therapists. Generally, this involves considering mechanisms such as auditory-motor interactions ( 55 ). For swallowing function, there are differences in the treatment direction due to the high involvement of more complicated timing and the movement of oral and pharyngeal regions. In the interventions included in this scoping review, vocal activities like humming and gliding, which were predominantly employed, went beyond mere warmup exercises and served as direct goal-oriented activities manifested by lengthy duration and the inclusion of multiple tasks during the vocalization phase of the intervention [i.e., ( 43 , 46 )]. Thus, for older adults with decreased muscular strength, a more proactive and efficient implementation of music applications should be developed to induce functional improvement.

4.1. Strengths and limitations

Scoping reviews inherently have limitations in thoroughly exploring the information extracted from their findings, as their primary focus is to outline the extent of published works on a given topic. Consequently, this particular review refrained from systematically evaluating the quality of the included studies. In terms of understanding the research topic, all authors are qualified music therapists and researchers with clinical experience in music therapy interventions targeting swallowing function. Notably, this review is the first of its kind to examine music interventions aimed at improving swallowing function; however, due to the limited availability of relevant research, there are limitations in extrapolating the specifics of these interventions. Since not all included studies were conducted by music therapists, there may be variations in the composition and level of expertise in interventions. Given the lack of prior research on music therapy interventions for presbyphagia, this analysis included different music-based interventions designed to enhance swallowing function across various groups of participants. From this approach, clinical implications were derived.

5. Conclusion

This scoping review holds the potential to enhance the efficacy of music therapists in addressing age-related swallowing disorders prevalent among the aging population. This research provides valuable insights for music therapists to respond more effectively to the challenges posed by age-related swallowing difficulties. Given that singing, a frequently employed musical activity within music therapy, shares structural elements with the phonation process, its utility in augmenting speech function is well understood. While singing to treat swallowing difficulties appears to parallel its application for speech enhancement, its direct extension to improving swallowing function is limited.

In the context of ameliorating age-related swallowing difficulties, it is essential to structure music therapy interventions that encompass precise muscular control and heightened execution intensity of anatomical structures intrinsically linked to swallowing function. It is anticipated that music therapy in clinical settings will witness a growth in treatment tailored to the indispensable mechanism of swallowing, consequently contributing to an enhanced quality of life for the older adult population.

Author contributions

SJK: Conceptualization, Data curation, Formal analysis, Investigation, Methodology, Writing – original draft, Writing – review & editing. MY: Conceptualization, Formal analysis, Validation, Writing – original draft, Writing – review & editing. SKi: Data curation, Formal analysis, Visualization, Writing – review & editing. SKa: Data curation, Validation, Visualization.

The author(s) declare that no financial support was received for the research, authorship, and/or publication of this article.

Conflict of interest

The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.

Publisher’s note

All claims expressed in this article are solely those of the authors and do not necessarily represent those of their affiliated organizations, or those of the publisher, the editors and the reviewers. Any product that may be evaluated in this article, or claim that may be made by its manufacturer, is not guaranteed or endorsed by the publisher.

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Keywords: swallowing, music intervention, singing, scoping review, older adults, presbyphagia

Citation: Kim SJ, Yeo MS, Kim SY and Kang SY (2023) A scoping review of music-based interventions for swallowing difficulties: implications for treating older adults with presbyphagia. Front. Med . 10:1285835. doi: 10.3389/fmed.2023.1285835

Received: 30 August 2023; Accepted: 16 October 2023; Published: 16 November 2023.

Reviewed by:

Copyright © 2023 Kim, Yeo, Kim and Kang. This is an open-access article distributed under the terms of the Creative Commons Attribution License (CC BY) . The use, distribution or reproduction in other forums is permitted, provided the original author(s) and the copyright owner(s) are credited and that the original publication in this journal is cited, in accordance with accepted academic practice. No use, distribution or reproduction is permitted which does not comply with these terms.

*Correspondence: Soo Ji Kim, [email protected]

This article is part of the Research Topic

Music Therapy in Geriatrics – Volume II

• Open access
• Published: 16 November 2023

Consideration of vaping products as an alternative to adult smoking: a narrative review

• Jane A. Foster 1  

Substance Abuse Treatment, Prevention, and Policy volume  18 , Article number:  67 ( 2023 ) Cite this article

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Tobacco harm reduction is a public health approach to reduce the impact of cigarette smoking on individuals. Non-combustible alternatives to cigarettes, such as electronic cigarettes (e-cigarettes), deliver nicotine to the user in the absence of combustion. The absence of combustion in e-cigarettes reduces the level of harmful or potentially harmful chemicals in the aerosol generated. This narrative review examines the published literature that studied the chemistry of e-cigarette aerosols, the related toxicology in cell culture and animal models, as well as clinical studies that investigated short- and long-term changes in biomarkers of smoke exposure after switching to e-cigarettes. In the context of the literature reviewed, the evidence supports the harm reduction potential for adult smokers who switch to e-cigarettes.

While smoking rates have decreased steadily over the past 20 years, approximately 22% (just less than 1 billion) of people aged 15 + worldwide smoke cigarettes, and smoking-related diseases accounted for 8.7 million deaths worldwide in 2019 [ 1 ]. Tobacco harm reduction is a public health approach to reduce the harm associated with smoking cigarettes. This approach provides smokers who do not quit with less harmful nicotine delivery products [ 2 ]. Non-combustible alternatives include heated tobacco products, nicotine-containing e-vapor products, and oral nicotine products can serve as options for adult smokers who switch to these alternatives and stop smoking. Heated tobacco products are non-combustible alternatives with electronic heating elements that heat tobacco to generate a tobacco vapor that delivers nicotine to the user (for review, [ 3 ]). Oral nicotine products deliver nicotine mainly by absorption through the user’s oral mucosa and include forms with and without tobacco (e.g., Snus and nicotine pouches, respectively) [ 4 ]. The non-combustible category of e-vapor products or electronic cigarettes (e-cigarettes) do not contain tobacco; they deliver nicotine to the user when a liquid is heated to form an aerosol (vapor) [ 4 ]. This literature review focused on this last type of non-combustible category: e-cigarettes and examined the scientific evidence that investigates whether switching from combustible cigarettes to e-cigarettes has the potential to improve health outcomes for adult smokers.

In the past 5 years, attention to e-cigarettes has increased with approximately 9300 peer-reviewed studies on the topic of vaping products (or e-cigarettes), as well as more than 650 review articles (Web of Science, “e-cigarette,” May 2023). Within the broad scope of research topics in the literature, the papers selected for this review focused on e-cigarettes in the context of key topics related to tobacco harm reduction, including aerosol chemistry studies, toxicological assessments of e-cigarette aerosols with in vitro and in vivo in comparison to cigarette smoke, and clinical investigations that examined the short- and long-term benefits of switching to e-cigarettes for adult smokers (Table 1 ). By focusing on studies that compare e-cigarettes to cigarettes, the objective of this review is to provide the reader with the current evidence related to the potential health benefits for smokers if they switch to e-cigarettes. Notably, it is important to understand the research evidence on the effects of switching from combustible cigarettes to e-cigarettes at several levels.

E-cigarettes/e-vapor products

While e-cigarettes are common and most individuals have some knowledge related to e-cigarettes, there are a lot of misconceptions and the history of their development is not well known. The first e-cigarette was sold in China in 2004, but the history of its development goes back to 1927 with the U.S. patent of an “electrical vaporizer” by Joseph Robinson [ 46 ]. Other milestones in e-cigarette/e-vapor product development are depicted in Fig.  1 and include the 1963 patent by Herbert Gilbert for a “smokeless non-tobacco cigarette.” In 1979, Phil Ray and Norman Jacobson conducted a clinical trial to test the feasibility of inhaling nicotine without smoke and coined the term “vaping” [ 46 ]. In 1985, Advance Tobacco Products Inc. commercialized a version of Ray/Jacobson’s device called “Favor,” but it was banned by the U.S. Food and Drug Administration (FDA) in 1987 [ 46 ]. The modern form emerged with the 2003 patent by Hon Lik for a nicotine delivery system that vaporized liquid to deliver nicotine to the user in an aerosol, leading to sales of the first e-cigarette in 2004 in China [ 46 ]. The technology of this first device is different from current devices on the market, but all of them use heat to vaporize a liquid and generate a nicotine-containing aerosol.

The history of the e-cigarette. Innovation and invention over the past century leading to the development of e-cigarettes, which were first sold in China in 2004. The timeline highlights some landmark events that contributed to the development of modern e-cigarettes (based on [ 46 ])

Types of e-cigarettes

There are three types of e-cigarettes on the market today: disposable self-contained devices, refillable devices, and pod-based devices (Fig.  2 ). Among these subcategories, there are numerous different devices and a wide range of e-liquid compositions, which makes generalization and comparison challenging. While the main components are similar, it is important to note that some devices are closed, whereas others have open systems that allow the user to add their own e-liquids. The broad range of e-cigarette devices and designs has resulted in regulatory challenges. Following their initial sale in China, e-cigarettes were distributed in Europe and the U.S. in 2006 [ 47 ] and are now available worldwide ( https://gsthr.org ). E-cigarette use has increased in the past decade – there were approximately 58 million e-cigarette users worldwide in 2020, representing 7.1% of the total population, and a sizeable increase from 1.7% estimated in 2012 [ 48 ].

E-cigarette types. Schematics showing the design of disposable, refillable, and pod-based e-cigarettes. (Reproduced with permission from Elsevier [ 4 ])

Toxicological assessment of e-cigarette aerosol

Cigarette smoke contains more than 6000 constituents [ 49 ], many of which are considered harmful or potentially harmful chemicals (HPHCs). Different regulatory authorities including the World Health Organization, Health Canada, and U.S. FDA have established lists of HPHCs that contribute to smoking-related diseases and should be considered in non-combustible alternative evaluation [ 8 ]. It is well-established that combustion of tobacco generates high levels of HPHCs that increase health risks and contribute to smoking-related diseases [ 50 ]. A key feature of reduced risk products (RRPs), such as e-cigarettes, is that these devices deliver nicotine to the user in the absence of combustion and hence were designed to reduce exposure to HPHCs compared to cigarette smoke [ 51 ]. Investigations reviewed here assessed whether switching to e-cigarettes present less risk than smoking: 1) compare the constituents of the aerosol from e-cigarettes to cigarette smoke, 2) examine the toxicity of aerosols in vitro using tissue culture approaches and in vivo using animal studies, 3) measure HPHC levels in blood and urine from individuals who switch to e-cigarettes and compare them with values in adult smokers, and 4) compare clinical biomarkers of exposure that are known risk factors for smoking-related diseases in individuals who switch to e-cigarettes and those who continue to smoke cigarettes.

Aerosol chemistry studies have shown reduced HPHC levels in some e-cigarette aerosols compared to cigarette smoke [ 5 , 6 , 7 , 9 ]. Notably, Ruyan, the company that marketed the first e-cigarette in China, reported reduced levels of several known HPHCs in their 2008 safety report [ 52 ]. It is important to note the standard lab methodologies for assessing e-cigarette aerosols have continued to be developed in the past decade, and many recent studies use the standards published in the CORESTA E-cigarette Task Force Technical Report [ 53 ]. Across several studies, levels of carbonyls and tobacco-specific nitrosamines were reduced by more than 90%. For example, the level of the carcinogen N-nitrosonornicotine (NNN) was detected at 0.05 ng/puff for an e-cigarette compared to 24.9 ng/puff for a reference cigarette [ 6 ]. A recent report measured a panel of carbonyl compounds, such as acetaldehyde, acrolein, and formaldehyde, and polycyclic aromatic hydrocarbons classified as carcinogenic or possibly carcinogenic in the aerosols from three e-cigarette products in comparison to cigarette smoke [ 9 ]. In this study, all of the carbonyl compounds measured were at very low levels in the e-cigarette aerosols; showing a 99% reduction in total carbonyl content compared to cigarette smoke [ 9 ]. Similarly, there was a 92–99% reduction in total polycyclic aromatic hydrocarbons in e-cigarette aerosols compared to cigarette smoke [ 9 ]. In a separate study, a comprehensive analysis of combustion-related HPHCs, including aromatic amines, volatile organic compounds, and polycyclic aromatic hydrocarbon benzo[a]pyrene, in e-liquids and their aerosols from commercially available e-cigarettes in the U.S. demonstrated that most of these HPHCs were at very low or below detectable levels in e-liquids or e-cigarette aerosols [ 10 ]. Part of the difficulty for the consumer and the non-expert scientist stems from the fact that there are so many different devices on the market, not all research study results apply to every device that is available. The above-noted reports provided evidence of reduced levels of HPHCs in e-cigarette aerosols compared to cigarette smoke, others have raised concerns about the levels of carbonyl compounds such as acetaldehyde, acrolein, and formaldehyde in aerosols generated by heating e-liquids, as well as metals that may be released from the device components [ 8 , 54 , 55 ]. These factors are important to consider and may represent risks associated with e-cigarette use more generally. Moreover, potential risks of excipients in e-liquids and additional potentially harmful chemicals generated from e-liquid heating have garnered attention. E-liquids contain a mixture of propylene glycol, vegetable glycerin, nicotine, flavors, and other constituents. A recent study examined 34 commercially available e-cigarette devices and demonstrated that levels of carbonyls, but particularly formaldehyde, varied across devices, whereas other HPHCs and selected metals were undetectable or very low in the e-cigarette aerosols [ 11 ]. The presence of carbonyl compounds, such as formaldehyde, in e-cigarette aerosols results from the heated degradation of e-liquid components (e.g., propylene glycol and glycerin) and depends on device features (e.g., closed vs open systems) and device settings (e.g., heating temperature and voltage) and result in higher HPHC levels in e-cigarette aerosols from some devices [ 11 , 56 , 57 , 58 , 59 ].

Understanding the toxicology of HPHCs in biological systems is an essential component of assessing their risks and benefits. To this end, several investigations have examined the toxicity of e-cigarette aerosols in tissue cultures and animal models. The results of these studies fall into three categories for discussion: 1) no toxicity observed, 2) less toxicity compared to cigarette smoke, and 3) alternative or negative findings.

In vitro studies

Several studies using tissue culture approaches reported no toxicity following exposure to e-cigarette aerosol, in comparison to the toxic effects observed in the same systems following exposure to cigarette smoke . Using an in vitro smoke/aerosol exposure system, exposure to e-cigarette aerosol from two commercial e-cigarettes had no mutagenic (Ames assay) or genotoxic effects (micronucleus assay) [ 12 , 13 ]. Another group performed scratch wound assays and reported no impact of e-cigarette aerosol on endothelial cell migration, compared to concentration-dependent inhibition following exposure to cigarette smoke [ 16 ]. The same group measured intracellular glutathione ratios, oxidant species generation, and activation of nuclear factor erythroid-related factor 2 (Nrf2)-controlled antioxidant response elements and did not detect oxidative stress in human bronchial epithelial cells exposed to e-cigarette aerosol extracts, whereas significant oxidative stress was found in cultures exposed to cigarette smoke [ 17 ]. Similarly, activation of the oxidative-stress related transcription factor Nrf2 and cytochrome p450 family member genes was observed in human coronary artery endothelial cells in response to cigarette smoke but not e-cigarette aerosol [ 18 ]. Several reports described no tissue damage or molecular changes in buccal and airway epithelial cultures exposed to e-cigarette aerosol compared to alterations observed following exposure to cigarette smoke [ 9 , 19 , 20 , 21 , 22 ]. The above-noted studies showed no detrimental impact of e-cigarette aerosol exposure on the cultures. Additional studies have demonstrated lower toxicity of e-cigarette aerosol compared to cigarette smoke. Significantly reduced (94–99%) cytotoxicity in human bronchial epithelial cells, measured using the neutral red uptake assay, was observed following exposure to e-cigarette aerosols compared to cigarette smoke [ 13 , 14 ]. Cigarette smoke negatively impacts airway epithelial cell function in vitro [ 23 ]. Exposure to e-cigarette aerosol did not impact cilia beat frequency in airway epithelial cells, but it did affect barrier integrity measured with trans-epithelial electric resistance (TEER), albeit to a lower degree than cigarette smoke [ 22 , 23 ]. A separate study showed a significant impact of e-cigarette aerosol on TEER following 10 days of exposure (compared to 24–48 h in the Haswell study) that was similar to cigarette smoke, suggesting that longer-term exposure to e-cigarette aerosol may have an impact on epithelial barrier function [ 24 ]. Differential gene expression analyses in donor-derived differentiated airway epithelial cells exposed to air, 3R4F smoke, or e-cigarette aerosol revealed that smoke induced significant upregulation of 873 RNAs associated with fibrosis, DNA damage signaling, oxidative stress response, and lung cancer [ 23 ]. In contrast, 113 differentially expressed RNAs were identified as responsive to the highest concentration of e-cigarette aerosol, but only 3 exceeded a fold change of 2 [ 23 ]. Similar findings were observed using RNA-sequencing in differentiated human bronchial epithelial cells and a human bronchial epithelial cell line [ 20 , 25 , 26 ]. Notably, a negative impact of e-cigarette aerosol on inflammatory processes in the cell lines was observed in one of these studies [ 20 ]. The potential for e-cigarette use to impact inflammation was recently demonstrated; e-cigarette users (including those who also used marijuana) had higher salivary inflammatory mediator levels compared to non-users [ 27 ]. Another group reported that exposure to e-cigarette aerosol was associated with cytotoxicity in human pulmonary fibroblasts, lung epithelial cells, and stem cells, but the authors did not include a cigarette smoke group for comparison [ 15 ]. In vitro studies reported impaired endothelial function and reduced epithelial function following exposure to both e-cigarette aerosol and cigarette smoke compared to air, underscoring that e-cigarette aerosol can impact physiological systems [ 28 , 29 ]. However, in the context of tobacco harm reduction, the collective evidence from numerous assays supports the hypothesis that e-cigarette aerosols are less toxic than cigarette smoke.

In vivo studies

Animal studies provide important results regarding the biological impact of HPHCs on host systems. Investigators have examined the effects of e-cigarette aerosols on key indicators in animal models known to be affected following exposure to cigarette smoke, including tissue histology, gene expression, cardiovascular function, oxidative stress, and inflammation [ 30 , 31 , 32 , 33 , 34 , 35 , 36 , 37 , 38 , 60 ]. Mice exposed to e-cigarette aerosols showed a reduced level of lung inflammation and a lower impact on cell proliferation compared to the cigarette smoke-exposed group [ 30 ]. In contrast, Sun and colleagues reported a comparable or greater number of histological lung lesions in mice exposed to e-cigarette aerosols versus cigarette smoke; an effect that was suggested to be associated with the acute increase in oxidative stress [ 31 ]. Atherosclerosis-prone apolipoprotein E-deficient ( Apoe-/-) mice are used as an animal model of atherosclerosis and more generally for understanding the pathophysiology of cardiovascular diseases [ 60 ]. A recent series of studies in this model system demonstrated reduced cardiovascular effects from exposure to e-cigarette aerosol compared to cigarette smoke, as well as smaller effects on biomarkers of exposure [ 32 , 33 , 34 , 35 ]. Long-term exposure up to 6 months yielded the expected negative effects of cigarette smoke on lung histology and function, as well as molecular or inflammatory changes. Conversely, no differences in lung function or histopathological changes were observed following exposure to e-cigarette aerosol, and less lung inflammation was observed in Apoe-/- mice [ 34 , 35 ]. In contrast, Ponzoni and colleagues reported similar alterations in gene expression in mice exposed to e-cigarette aerosol or cigarette smoke [ 37 ]. Another group reported greater negative cardiac effects in rats exposed to e-cigarette aerosols compared to cigarette smoke [ 36 ]. One recent study found a significant impact of long-term exposure to e-cigarette aerosol on nicotine levels and nicotine-related gene expression in the mouse brain compared to air (no comparison to smoke), highlighting the importance of determining the potential risks associated with continued use of nicotine over time [ 38 ]. Certainly, longitudinal studies are needed to clarify the acute effects of e-cigarette aerosols.

Clinical studies

Beyond cell culture and animal studies, it is critical to measure HPHC levels in human biospecimens such as saliva, blood, and urine to provide critical evidence of the potential for reduced risk for adult smokers who completely switch to e-cigarettes. Using a within-subject study design, biomarkers of exposure, including carbon monoxide, nicotine, and acrolein, were measured in urine from smokers before and after switching to e-cigarettes. The results showed reduced levels of all biomarkers at 4 weeks after switching, as well as reduced levels in dual users who did not completely switch to exclusive e-cigarette use [ 39 ]. In a similar study, an examination of 7 nicotine metabolites and 17 HPHCs in urine of smokers before and 2 weeks after switching to e-cigarettes revealed that nicotine and some polycyclic aromatic metabolites remained the same after 2 weeks; however, levels of most HPHCs were significantly decreased [ 40 ]. In a cross-sectional study that focused on HPHCs in salivary and urine samples, detected salivary levels of N 1 -nitrosonornicotine (NNN) in e-cigarette users overlapped with those measured in cigarette smokers, but urine levels of NNN were very low or not detectable in e-cigarette users [ 41 ]. As noted above, concern about exposure to metals from the metallic heating device in e-cigarettes warrants attention. A study that detected metals in e-liquid and aerosols from e-cigarettes reported increased levels of copper, chromium, tin, and lead in urine of e-cigarette and dual users compared to non-users; however, no metals were detected in hair samples of e-cigarette users [ 42 ].

Clinical studies have also been undertaken to measure biomarkers of exposure that are known risk factors for smoking-related diseases in individuals who switch to e-cigarettes compared to those who continue to smoke cigarettes. Biomarkers of exposure provide quantifiable measures of biological changes in individuals who smoke. Assessing changes in these biomarkers in individuals who switch to RRPs is central to demonstrating the potential for harm reduction for the individual. Blood carboxyhemoglobin—a biomarker for the HPHC carbon monoxide—was reduced by 70–97% as soon as 5 days after switching to e-cigarettes [ 43 , 44 ]. Notably, 14 of the 23 biomarkers of exposure were significantly reduced in adults who switched to e-cigarettes compared to their baseline levels measured when they were smoking cigarettes [ 43 , 44 ]. Another study demonstrated reduced urinary levels of 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanol (NNAL) in smokers who switched to e-cigarettes exclusively, as well as in dual users who reduced the number of combustible cigarettes over the 24-week study [ 45 ]. The results of clinical studies showing reduced levels of HPHCs and biomarkers of exposure in adult smokers who switch to e-cigarettes provide a base of evidence of the role these products can play in tobacco harm reduction.

User surveys suggested that the benefits of using of e-cigarettes by smokers included less cigarette consumption, help with smoking cessation, and reduced craving and withdrawal symptoms [ 61 , 62 ]. A recent study examined the safety profile of e-cigarette use over a 2-year period and demonstrated reduced exposure to HPHCs, and use was not associated with any clinical health concerns including lung function and nicotine withdrawal effects [ 63 ]. However, other clinical studies investigating short-term effects on cardiovascular and lung function in e-cigarette users highlighted potential risks associated with e-cigarette use. One study examined vascular function, which is associated with cardiovascular disease, was similar between cigarette smokers and sole e-cigarette users [ 64 ]. Another study showed similar increased levels of heart rate variability in cigarette and e-cigarette users, but acute blood pressure increases observed in cigarette smokers were not found in e-cigarette users [ 65 ]. In contrast, Barna and colleagues demonstrated that e-cigarette use had no effect on respiratory function measured as persistent alveolitis, which was evident in cigarette smokers [ 66 ]. Importantly, individual differences in smoking behavior and other lifestyle factors need to be considered when assessing the risks and benefits of e-cigarette use.

Conclusions

In summary, there is significant evidence to support the role of e-cigarettes in tobacco harm reduction, but these non-combustible alternatives are not risk free. The long-term risks associated with cigarette smoking are well established, and the best choice for adult smokers is to quit smoking. That said, for individuals who are not able to quit, non-combustible alternatives such as e-cigarettes represent an excellent alternative. While the long-term epidemiological data related to alternatives such as e-cigarettes are not yet available, cancer and non-cancer disease risk estimates for long-term use of non-combustible devices suggest reduced disease risk compared to cigarette smoking [ 67 , 68 ]. Moving forward, more research is needed to better understand the long-term impact of e-cigarettes on biomarkers of exposure, as well as the effects of long-term e-cigarette use on cardiovascular health and disease outcomes.

Availability of data and materials

Not applicable.

Abbreviations

Apolipoprotein E

• Electronic cigarette

Food & Drug Administration

Harmful or potentially harmful chemical

4-Methylnitrosamino)-1-(3-pyridyl)-1 butanol

N 1 -Nitrosonornicotine

Nuclear factor erythroid factor 2

Reduced risk product

Trans-epithelial electric resistance

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Foster, J.A. Consideration of vaping products as an alternative to adult smoking: a narrative review. Subst Abuse Treat Prev Policy 18 , 67 (2023). https://doi.org/10.1186/s13011-023-00571-w

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DOI : https://doi.org/10.1186/s13011-023-00571-w

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