Open access Review What is the meaning of health literacy? A systematic review and qualitative synthesis Chenxi Liu,1 Dan Wang,1 Chaojie Liu ,2 Junnan Jiang,1 Xuemei Wang,1 Haihong Chen,1 Xin Ju,1 Xinping Zhang1 To cite: Liu C, Wang D, Liu C, AbstrACt services.10 Inadequate health literacy is asso- et al. What is the meaning of The objective of this review was to clarify what health ciated with difficulties in comprehension of health literacy? A systematic literacy represents. A systematic review with qualitative health information, limited knowledge of review and qualitative syntheses was performed (CRD42017065149). Studies diseases and lower medication adherence, synthesis. Fam Med Com Health concerning health literacy in all settings were included. 2020;8:e000351. doi:10.1136/ which contribute to poor health, high risk Studies before 15 March 2017 were identified from fmch-2020-000351 of mortality, insufficient and ineffective use PubMed, Medline, Embase, Web of Science, Scopus, ► Additional material is PsycARTICLES and the Cochrane Library. The included of healthcare, increased costs, and health published online only. To view disparities.4 6 11 The existing evidence seems literature either had defined the concept of health please visit the journal online literacy or made a detailed explanation of health literacy. to suggest health literacy as one of the most (http:// dx. doi. org/ 10. 1136/ fmch- A total of 34 original studies met the inclusion criteria, promising and cost- effective approaches to 2020-0 00351). including 13 involved in previous systematic reviews overcome the NCD challenges.12 13 Many and 21 new studies. Health literacy was commonly countries have included health literacy as a conceptualised as a set of knowledge, a set of skills or key priority in their policies and practices, a hierarchy of functions (functional- interactive- critical). such as the USA, Canada, Australia, the The construct of health literacy covers three broad European Union and China.14 The WHO elements: (1) knowledge of health, healthcare and recommends health literacy as an instru- health systems; (2) processing and using information in ment for achieving several key targets listed various formats in relation to health and healthcare; and (3) ability to maintain health through self- management in the Sustainable Development Goals.15 and working in partnerships with health providers. Despite the realisation of the importance Health literacy is defined as the ability of an individual of health literacy to human health and exten- to obtain and translate knowledge and information in sive studies into this area over the past few order to maintain and improve health in a way that decades, there is still a lack of consensus is appropriate to the individual and system contexts. on ‘what the concept actually represents’.16 This definition highlights the diversity of needs from Such an essential research question has often different individuals and the importance of interactions been overlooked.13 The concept of health between individual consumers, healthcare providers and literacy seems to be very flexible, which allows healthcare systems. anyone to identify nearly whatever one wants as health literacy. Over 250 different defini- IntroduCtIon tions exist in the academic literature.17 The © Author(s) (or their Health literacy, as a term first proposed in unclear and inconsistent interpretations employer(s)) 2020. Re- use the 1970s,1 generally concerns whether an of health literacy are projected to limit the permitted under CC BY- NC. No individual is competent with the complex development of valid and reliable measure- commercial re-u se. See rights and permissions. Published by demands of promoting and maintaining ments, the accurate evaluation and compar- BMJ. health in the modern society.2 Over the past isons of health literacy initiatives, and the 1School of Medicine and Health two decades, increasing attention has been synthesis of evidence to support strategies for Management, Huazhong attached to the concept due to its significant improving health literacy.13 14 16–18 Further- University of Science and benefits to individual and public health and more, the confusion of the concept is likely Technology Tongji Medical the sustainability of healthcare systems.3–8 It to produce disjointed and even contradictory College, Wuhan, China 2Public Health, La Trobe is considered particularly important when findings, jeopardising the development and University, Melbourne, Victoria, non- communicable diseases (NCDs) prevail implementation of trustworthy and effective Australia and their corresponding costs are steadily health literacy-r elated interventions and poli- rising,9 highlighting the need for people to cies.13 14 16 Correspondence to Professor Xinping Zhang; take more responsibility in managing their This study aimed to clarify ‘what health xpzhang602@ hust. edu. cn own health with more effective use of health literacy represents’ through a systematic Liu C, et al. Fam Med Com Health 2020;8:e000351. doi:10.1136/fmch-2020-000351 1Open access review and qualitative synthesis of existing studies across In the first step, included studies were repeatedly read, different contexts in relation to this complex concept. and all statements relevant to the research question were identified using the data collection chart, forming a data pool for qualitative syntheses. A total of 570 statements Methods were recorded. search strategy and selection criteria In the second step, each statement was divided into several A systematic review following a registered protocol (no: parts using a semigrammatical coding approach, which CRD42017065149) was conducted, which followed the included cores, actions, objects, aims and others (such as ENTREQ (Enhancing Transparency in Reporting the context). For example, Freedman et al22 interpreted health Synthesis of Qualitative research) guidelines. The search literacy as ‘the skills necessary to obtain, process, evaluate, strategy was adapted based on a previous systematic and act upon information needed to make public health review,5 using a combination of keywords such as ‘health decisions that benefit the community’. This statement literacy’, ‘definition’, ‘concept’ and so on. We searched was coded as ‘necessary skills’ (cores), ‘to obtain, process, PubMed, Medline, Embase, Web of Science, Scopus, evaluate and act upon’ (actions), ‘needed information’ PsycARTICLES and the Cochrane Library and restricted (objects), and ‘to make public health decisions that benefit our search to articles published from 1 January 2010 to 15 the community’ (aims). March 2017 (date of last search) simply because the most The third step extracted shared common themes. The recent systematic review analysed literature published clustering procedure was mainly based on the codes (n=74) before 2010 (details of the search protocol in online labelled as ‘cores’, but also considered other codes (actions, supplementary table S3). objects, aims and others) embodied in each statement. Title, abstract and full texts of retrieved records were Finally, the extracted themes were reviewed against the examined by two authors against the inclusion and exclu- initial coding and data pool and renamed if necessary. sion criteria, independently. Discrepancies, if occurred, This was to ensure that the data pool was well represented were resolved through consultations with the third author. and the relationships between codes and themes were not The included literature either had an explicit objec- distorted. tive to define the concept of health literacy or made an Two reviewers conducted steps 1 and 2 independently, implicit contribution to people’s understanding of health and their results were crosschecked and reconciled literacy: for example, studies that explored the constructs through negotiations. Steps 3 and 4 were conducted in of health literacy. Studies with an interpretive nature groups. Consensus was achieved through constant negoti- using an existing conceptual framework without making ations and discussions within the research team. further contributions to the conceptualisation of health literacy, without any theoretical presentation of the concept of health literacy and those that were not written results in the English language were excluded. Characteristics of included studies Additional studies were identified at this stage through A total of 6029 records were retrieved from the databases scrutinising references of the included literature. These and 2368 duplications were removed. After screening included studies published before 2010 but had been of titles and abstracts, 589 studies were kept for full-t ext omitted in the two previous systematic reviews.5 19 reviewing. The full- text reviews identified 569 studies that failed to meet our inclusion criteria: 394 due to a data analysis lack of conceptualisation; 139 due to their interpretive A data collection chart (online supplementary table nature for existing conceptual frameworks; 3 due to S4) was developed and guided the extraction of the a lack of interpretations of the concept; and 33 due to bibliographic information and the results of the concep- language barriers (non-E nglish publications). We then tualisation of health literacy in the included studies. added the 13 studies included in the two previous system- The bibliographic information covered study objectives atic reviews.5 19 One more study was identified from refer- and methods, describing why and where the study was ences screening. This resulted in a final sample size of 34 undertaken, who participated in the study, and how data for our systematic review (figure 1). were collected and analysed. The results of the concep- About two-t hirds of the included studies explored tualisation of health literacy focused on the underlying the concept of health literacy in general popula- constructs and meaning of health literacy.5 19 Two of the tions,3–5 19 20 22–37 while the others focused on children and authors extracted data independently. The two sets of adolescents,38–42 elderly people,43 patients with chronic chart were crosschecked and eventually amalgamated diseases,44–47 gay men,48 cancer caregivers,49 and people through group discussions. with limited English proficiency.50 Most studies adopted A data- driven thematic analysis was adopted using a a broad and general concept of health literacy without semigrammatical coding approach.20 According to Braun restricting to a specific health topic. But eight studies and Clarke,21 this involved four steps: data familiarisation, placed the concept of health literacy under a particular initial coding, themes searching, and themes reviewing context, such as public health,22 sexual health,48 tobacco and naming. control,41 complementary medicine,37 verbal exchange of 2 Liu C, et al. Fam Med Com Health 2020;8:e000351. doi:10.1136/fmch-2020-000351Open access Figure 1 ENTREQ flow diagram of systematic review. information,35 functional health47 and critical thinking34 36 knowledge, procedural knowledge and judgement skills. (online supplementary table S1). Declarative knowledge represents people’s understanding Of the 34 included studies, 19 involved original of factual information about health, while procedural data4 5 19 20 23 24 26 28 32 35–37 39 41–44 48 49 and 15 were theoretical knowledge represents people’s understanding of rules proposals.3 22 25 27 29–31 33 34 38 40 45–47 50 The former performed that guide people’s reasoned choices and actions. In concept analyses,28 32 36 43 concept mapping,23 49 thematic combination, they enable people to acquire and use infor- analyses,5 19 24 35 41 42 48 grounded theory analyses,26 35 39 mation in various contexts and govern the competence semigrammatical analyses20 or framework analyses44 on of different tasks.25 Similarly, Paakkari and Paakkari38 qualitative data collected from documents, interviews or defined health literacy as a set of theoretical knowledge, focus groups. The latter were largely views from experts, practical knowledge and critical thinking, corresponding with limited information about how the conceptuali- to declarative knowledge, procedural knowledge and sation was done. Those theoretical studies were usually judgement skills proposed by Schulz and Nakamoto.25 published before 2013 during the early stage of argu- In addition, Paakkari and Paakkari38 argued that self- ments about the concept of health literacy. Since then, awareness and citizenship also form a part of health the literature has been dominated by empirical studies literacy because they represent one’s ability to assess (online supplementary table S1). oneself in an informed way and to take responsibility to What is health literacy? improve health beyond a personal perspective. Rowlands Health literacy was commonly conceptualised as a set et al24 found that health literacy is reflected in people’s of knowledge, a set of skills or a hierarchy of functions ability to acquire, understand and evaluate knowledge (functional- interactive- critical). for health. Shreffler- Grant et al37 specified the knowledge Four studies highlighted knowledge as the core in the regarding the dosage, effect, safety and availability of concept of health literacy. Schulz and Nakamoto25 iden- medicines as health literacy associated with complemen- tified health literacy as a set of basic literacy, declarative tary medicines (online supplementary table S1). Liu C, et al. Fam Med Com Health 2020;8:e000351. doi:10.1136/fmch-2020-000351 3Open access Arguably, the Institute of Medicine (IoM) presented functional health literacy—understanding basic health one of the most influential models of health literacy. concepts, comprehending the relationship between The IoM model contains four underlying constructs: health behaviours and health outcomes, and performing cultural and conceptual knowledge, print health literacy basic health behaviours; interactive health literacy— (writing and reading skills), oral health literacy (listening maintaining good relationships with peers, appropriately and speaking), and numeracy.4 It has a strong focus on expressing oneself and responding to others, and suffi- the required skills for people to obtain, process and ciently understanding a variety of information from the apply information for the purpose of medical care. This environment; critical health literacy—assessing, analysing model has attracted support from many researchers. and predicting the influence of health information of all For example, Baker30 refined the contents of health- types and responding appropriately (online supplemen- related print literacy and oral literacy in general popula- tary table S1). tions. Harrington and Valerio35 refined details of verbal Apart from the abovementioned models, some exchange of health information, similar to the concept of researchers attempted to conceptualise health literacy oral health literacy. Yip50 argued that speaking, reading, from other perspectives. Drawn on experts’ views, Soellner writing, listening and numeracy are particularly important et al23 proposed addition of self- perception, proactive for people with limited English proficiency. Squiers et al19 approach to health, self- regulation and self- control into added negotiation skills into oral health literacy and rela- the concept of health literacy. By contrast, Jordan et belled it as communication skills. Navigation skills were al26 examined the views of patients and proposed three also proposed by Squiers et al19 as an important element in dimensions of health literacy: identifying a health issue the eHealth context. Sørensen et al summarised the liter- (knowing when and where to find health information), ature and presented skills to access, understand, appraise engaging in information exchange (verbal communi- and apply information and knowledge as four core skills cation skills, assertiveness and literacy skills) and acting of health literacy, which can cover all related works that on health information (capacity to process and retain people need to carry on when dealing with health infor- information, and application skills). Buchbinder et al20 mation to improve and maintain health.5 Mancuso28 and combined the views from both patients and health profes- Oldfield and Dreher43 emphasised the importance of sionals and summarised health literacy as knowledge, atti- comprehension skills. Speros32 further added successful tude, attribute, relationship, skills, actions and context functioning in the patient role as a core construct of in relation to 16 aspects such as diseases, health systems, health literacy (online supplementary table S1). information and others. Several studies emphasised some Several studies viewed health literacy as a hierarchy special elements critical to a particular population: for of functions, which require different levels of social and example, consistency, delivery and contents of informa- cognitive skills. Nutbeam3 first proposed the three-l evel tion for sexual health of gay men48; self- management model: functional health literacy, interactive health literacy skills and active involvement in consultations for patients and critical health literacy. This model was further clari- with chronic diseases44; relationships and support systems fied and expanded by several researchers.34 36 40–42 45 47 In for cancer caregivers49; patient–provider relationship Nutbeam’s prototypical model, functional health literacy and preventive care (indicating a proactive approach to refers to ‘basic skills in reading and writing to enable health); and the rights and responsibilities (capturing individuals to function effectively in everyday situations’; principles of self- efficacy and empowerment to manage interactive health literacy covers ‘more advanced skills to one’s health environment) for adolescents.39 Freedman extract information and derive meaning from different et al focused on public health literacy and proposed civic forms of communication, and to apply new information orientation, indicating skills and resources needed to to change circumstances’; critical health literacy requires address health concerns by civic engagement, as one of ‘the highest- level of skills to critically analyse and use the aspects of health literacy.22 Zarcadoolas et al31 added information to exert greater control over life events science literacy (competence with science and tech- and situations’.3 Schillinger47 interpreted functional nology) and cultural literacy (ability to notice and use health literacy as literacy and numeracy. Chinn34 consid- various beliefs, customs and values) as common features ered critical health literacy as the function of under- required for interpreting and acting on health informa- standing social determinants of health and engaging in tion (online supplementary table S1). collective actions. Sykes et al believed that critical health literacy covers advanced personal skills, health knowl- elements of health literacy edge, information skills, effective interactions between The thematic analysis extracted three key themes that are service providers and users, informed decision making, well representative of the various models adopted in the and empowerment including political actions.36 Manga- included studies: (1) knowledge of health, healthcare and nello40 added media literacy, the ability to critically assess health systems; (2) processing and using information in media messages, as a separate construct into health various formats in relation to health and healthcare; and literacy for adolescents to highlight the importance of (3) ability to maintain health through self- management media use in the specific population. Liao et al42 exam- and working in partnerships with health providers (online ined the meaning of the Nutbeam model in children: supplementary table S2). 4 Liu C, et al. Fam Med Com Health 2020;8:e000351. doi:10.1136/fmch-2020-000351Open access Knowledge of health, health care and health systems efforts put in executing the tasks.20 23 26 28 36 38 39 49 Two The theme of knowledge refers to the understanding components emerged from the subtheme ‘self-e fficacy of factual information about health and can be further in health actions’: self-c onfidence and accountability. divided into four aspects, namely knowledge of medi- Self- confidence indicates the following psychological cine, knowledge of health, knowledge of health systems features: articulating oneself bravely, questioning health- and knowledge of science.4 20 22 23 25 31 34 36–39 42–44 49 Knowl- care providers and ensuring full comprehension of edge of medicine refers to the understanding of infor- health information by asking for further clarifications. mation under the medical context, such as medications, Accountability refers to one’s attitudes towards her/his treatments and illness states, while knowledge of health own health and willingness to take responsibilities in is focused on understanding information in regard to managing her/his health. Self-e fficacy determines how a health under everyday situations, for example, healthy person perceives health and applies health information behaviours, healthy lifestyle, health terms and public in health actions (online supplementary table S2). health. Knowledge of healthcare systems refers to the Provision of health information (active engagement in understanding of information about the basic structure dissemination of consistent information in a language that is and available services of a health system, which helps appropriate to consumers) people use the system in a more effective and efficient Consumer communication and participation is important way. Finally, knowledge of science refers to the under- in all levels of health actions.20 30 39 48 49 Baker argued standing of fundamental scientific concepts and scientific that the complexity of health information can become arguments (online supplementary table S2). a serious barrier for people to engage in healthcare.30 There is a consensus that consumers need to participate Processing and using information in various formats in relation to in the generation and dissemination of health informa- health and healthcare tion in order to ensure the simplicity, consistency and This theme concerns whether people are able to process accuracy of the presentation and dissemination of health and use information in relation to health and healthcare information. The approach to provision of information effectively. It can be further divided into four subthemes: may help or hinder people’s understanding, processing ability to process and use information to guide health and use of information. actions, self-e fficacy in processing and using health infor- mation, provision of health information (active engage- Access to resources and support for processing and using ment in dissemination of consistent information in a information language that is appropriate to consumers), and access to Resources and support are essential not only for realising resources and support for processing information. one’s own ability in processing and using knowledge and information in health actions, but also for complementing Ability to process and use information to guide health actions one’s shortcomings in processing and using information. This subtheme refers to the multidimensional skill set Statements in relation to this subtheme were first treated that is necessary for dealing with and applying informa- as a component of health literacy by Freedman et al.22 The tion in health actions. It has been widely accepted as an contents of this subtheme were further clarified by several essential component of health literacy in the existing liter- other researchers,20 24 36 49 covering four aspects: access ature. The skill set contains general skills of literacy and to health information and information infrastructure numeracy, such as reading, writing, numeracy, listening (eg, library and online services), information support and speaking, as well as special skills for obtaining, under- from healthcare providers, information support from standing, appraising, communicating, synthesising and social networks (family, friends, colleagues and commu- applying health- related information. A health- literate nity organisations), and external resources (eg, financial consumer knows when and where to seek, find and retrieve resources and time committed to processing and use of printed information and whom to talk to for information information) (online supplementary table S2). advice; is able to comprehend the meaning of obtained information; and can assess the credibility and scientific Ability to maintain health through self-management and working in context of the information and its relevance to oneself. partnerships with health providers The skill set also enables the consumer to share obtained This theme refers to one’s ability of using her/his knowl- information with others and express her/his own prefer- edge and information skill set to effectively manage ences effectively. The ability to compare, contrast, weigh health and illness conditions.20 23 28 38 42 This often up and integrate relevant information is required for the involves both self- management and working in part- purpose of applying the information in making decisions nerships with health providers, requiring abilities of at the individual level and/or at the societal level (online self- regulation, goal achieving and interpersonal skills. supplementary table S2). Self- regulation encompasses self- perception (awareness Self-efficacy in processing and using health information of one’s own situation and preferences), self- reflection Self- efficacy is a psychological concept which refers to (critical analysis of oneself) and self- control (ability to one’s belief in one’s ability to succeed and subsequent control oneself). Self-r egulation is critical to enable one Liu C, et al. Fam Med Com Health 2020;8:e000351. doi:10.1136/fmch-2020-000351 5Open access to obtain individual- tailored information and apply the the declarative/theoretical knowledge covers knowledge information in a way that is appropriate to oneself. The of medicine, knowledge of health, knowledge of health- ability of goal achieving refers to a series of skills, based care systems and knowledge of science. on which people can set meaningful health goals, adjust The concept of health literacy has been evolving over strategies and eventually attain the goals. Interpersonal the past decade. It started with a doubt about the useful- skills are associated with one’s ability to understand, ness of ‘information and knowledge’, simply because a respect, listen and respond to others, and to build and highly knowledgeable person may not be able to mate- maintain a harmonious relationship with them (online rialise the benefits of acquired information/knowl- supplementary table S2). edge.20 23 26 49 As a result, some researchers recommended the addition of self-e fficacy as a component of health literacy. Self- efficacy reflects the confidence and willing- dIsCussIon ness of one in using information/knowledge for health In this study, we synthesised the results of 34 studies and actions. Some researchers proposed further expansion found that health literacy has been commonly viewed as a of the concept of health literacy, pushing it beyond the set of knowledge, a set of skills or a hierarchy of functions confinement to individual abilities.20 30 48 49 Health knowl- (functional-i nteractive- critical). Three themes emerged edge is usually produced by health professionals, while from the 34 studies in regard to the concept of health consumers are seen as passive recipients of knowledge. literacy: (1) knowledge of health, healthcare and health The language and clauses used by health professionals systems; (2) processing and using information in various are often difficult, if not impossible, for consumers to formats in relation to health and healthcare; and (3) understand.48 This has resulted in a great deal of frus- ability to maintain health through self-m anagement and tration in the interaction between health providers and working in partnerships with health providers. consumers, prompting calls for increasing engagement of Health literacy started as a concept associated with the consumers in the synthesis and dissemination of knowl- individual ability in obtaining information and knowl- edge information. edge to support health actions. Not surprisingly, all of the The conceptual expansion of health literacy came as included studies examined the concept of health literacy a result of empirical enquiries into the meaningfulness from the ‘information and knowledge’ perspective. The of health literacy. Several studies explored the meaning ability of an individual to process and use information to of health literacy from the perspectives of different guide health actions has been a major concern of those populations. Unlike the theoretical analyses at an early studies. stage, these studies present empirical evidence for advo- Health literacy has been commonly interpreted as cating a change in the concept of health literacy.12 18 The an ability to use general literacy skills (reading, writing, ability to maintain health using acquired information numeracy, listening and speaking) in obtaining, under- and knowledge is the utmost goal of the development of standing, appraising, synthesising, communicating health literacy. This requires one to understand her/his and applying health- related information. The previous own ability and situation and work in partnerships with systematic review identified ‘accessing, understanding, others for achieving the best possible outcomes. Evidence appraising, communicating and applying’ health infor- from the UK shows that most patients, caregivers and mation as the five core components of health literacy.5 health workers consider health literacy as a ‘whole But it ignores the fundamental role of general literacy system outcome’ rather than an attribute of individ- skills,4 which can actually shape the needs and the way uals.51 Edwards et al52 argued that one can acquire knowl- of one obtaining and using health- related information. edge from others without necessarily going through the For example, a person with a high level of knowledge and entire information processing process. When a person is writing skills may not necessarily be able to convey infor- looked after by a group of people from the family, the mation effectively in verbal conversations. The literature workplace, the health facility and the community, group also suggests that ‘information synthesising’ is missing in health literacy appears to be even more important than the previous systematic review.5 19 ‘Information synthe- individual health literacy. Access to resources and support sising’ is particularly important in the information era, can serve as a proxy indicator of ‘group health literacy’. where people are inundated with enormous amount of This study makes a significant contribution to the information. Under such circumstances, people should conceptualisation of health literacy. Pleasant13 points out be able to compare, weigh up and integrate various infor- that none of the existing definitions of health literacy mation to make an informed decision. were generated through a robust and rigorous scien- Knowledge can be considered as a result of information tific approach. The widely used original definition of translation, or a precursor that determines how informa- health literacy, based on the individual ability to process tion is processed and used.25 38 Schulz and Nakamoto25 and use information for health gains, has failed to find and Paakkari and Paakkari38 categorised knowledge into its evidence support from an increasing body of recent declarative/theoretical knowledge and procedural/prac- empirical studies. We propose a renewed definition of tical knowledge. In this study, the latter one is grouped health literacy, incorporating all relevant themes iden- into the theme ‘processing and use of information’, while tified from the existing studies. Health literacy is “the 6 Liu C, et al. Fam Med Com Health 2020;8:e000351. doi:10.1136/fmch-2020-000351Open access ability of an individual to obtain and translate knowl- Funding The authors have not declared a specific grant for this research from any edge and information in order to maintain and improve funding agency in the public, commercial or not- for- profit sectors. health in a way that is appropriate to the individual and Competing interests None declared. system contexts’. This definition highlights the diversity Patient consent for publication Not required. of needs from different individuals and the importance Provenance and peer review Not commissioned; externally peer reviewed. of interactions between individual consumers, healthcare open access This is an open access article distributed in accordance with the providers and healthcare systems for maintaining health. Creative Commons Attribution Non Commercial (CC BY- NC 4.0) license, which The whole- system view can help people better understand permits others to distribute, remix, adapt, build upon this work non-c ommercially, the role of health literacy and what needs to be done for and license their derivative works on different terms, provided the original work is properly cited, appropriate credit is given, any changes made indicated, and the use improving health literacy. Such a whole- system view has is non- commercial. See: http:// creativecommons. org/ licenses/ by- nc/ 4. 0/. been advocated by more and more researchers and prac- tices.53 54 orCId id Chaojie Liu http:// orcid. org/ 0000- 0002- 4870- 4520 limitations There are several limitations to this study. First, the included reFerenCes literature was limited to those published in English. 1 Simonds SK. Health education as social policy. 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