Introduction
Type-II Diabetes Mellitus (hereafter referred to as diabetes) is the most prevalent form of diabetes, and about 422 million adults are affected, worldwide [
1]. In some regions, such as the Middle-East and North Africa [
2] (MENA) countries, including Iran [
2,
3], the burden of diabetes has been on the rise [
4]. The continual rise in the burden of diabetes is perplexing because countries, since long, have national public education and prevention programs on diabetes [
5].
To have an effective and adequate intervention for the prevention of diabetes, the fulfilment of at least three conditions is suggested. First, the interventions address the public at large, such as through public education on diabetes. Second, the use of prescribed theoretical frameworks while designing interventions [
6]. Third, the interventions should address the majority of underlying pathogenic mechanisms. Public education is considered a powerful tool in the primary prevention of diabetes [
7]. Public health knowledge is an important component of health literacy, which bears significance in improving the prevention of diseases [
6]. The public’s health education can also improve one’s cognitive levels, unhealthy attitude and behaviors, prevention awareness, and acceptance of scientific concepts [
7]. Advocacy agencies, such as the International Diabetes Federation, also suggests self-care measures (such as following a healthy diet) for optimal control of blood glucose [
8]. In the absence of adequate self-care behaviors, there is a risk of premature mortality and complications among those with diabetes [
9]. Therefore, community-based educational programs may be helpful in addressing various aspects of the patients’ health status including health behaviors, diet and physical activity [
10], and quality of life [
11] as well. Such programs show promise in T2DM prevention [
12], as they can reach general populations that are not included in conventional healthcare settings, and usually target various groups within a community [
13]. They may be also helpful in identifying the protective factors within different cultures, which may lead to provision of more support for the patients within the community [
14].
Similarly, interventions are an embodiment of theories [
15]. Theories help to make sense of complex phenomena by providing tentative explanations of the reasons and circumstances behind particular behaviors. Interventions can then target those behaviors. Others have also shown that adhering to a rigid theoretical framework is both recommended [
6] and beneficial [
16] because theoretically informed interventions lead to better outcomes. As an example, the health belief model [
17] is useful in explicating self-care activities such as diabetes management recommendations and has a focus on behavior related to the prevention of disease.
Several current systematic reviews [
11,
13,
18] have reported the positive effects of community-based programs on diabetes prevention. Obviously, a significant number of community-based programs may not involve educational interventions aiming at lifestyle change [
13]. In previous systematic reviews and meta-analyses [
11,
13,
18], however, no differentiation was considered between the community-based interventions with or without educational program. There is also a scarcity in the consolidated data describing the outcomes of community-based educational interventions, and in particular by theoretical framework, considerations on community factors, and intervention delivery method. It is also unknown that which behavior change theories and models are more practical and useful in such interventions. In other words, to the best of our knowledge, there has not been any globally focused systematic analysis of community-based interventional outcomes related to the prevention of diabetes through the necessary simultaneous perspective of public education and theoretical frameworks. Thus, the primary objective of our study was to estimate the change in community-based education interventions throughout the world that may effectuate in risk parameters of diabetes, including diabetes incidence rate, fasting blood glucose, and hemoglobin A1c. Our secondary objectives were to estimate any possible change in secondary diabetes risk parameters, including body weight, body mass index, waist circumference, and systolic and diastolic blood pressure. Moreover, we tried to determine the role that gender, age, duration of follow-up, and the use of a theoretical framework may play in conveying a change in diabetes risk. We believe our work would provide a comprehensive summary of available research to help have better anti-diabetes interventions and policies for safeguarding the health of the communities throughout the world.
Discussion
Based on our results, we found that studies testing for educational interventions against diabetes are few. Nevertheless, such interventions (number of participants = 16,106) can reduce diabetes incidence by 46.0%, along with causing favorable changes in the mean levels of FBS and A1c, BMI, and waist circumference. The interventions were effective for both genders, but men in particular, and the use of theory-based interventions. There was no effect of such interventions on both systolic and diastolic blood pressure, and the effect of interventions did not vary with the duration of follow-up. The most frequent theories used for interventions were social cognitive, t5 instructional design, health belief, and social marketing theories.
It was essential to conduct this study because diabetes has a huge affected and at-risk population. So, given the sheer size of the diabetes problem, primary prevention is the only way by which the public health burden from diabetes can be reasonably reduced or controlled. Moreover, many regions, such as ours, are showing a considerable rate of increase in diabetes than elsewhere. Thus, newer empirical evidence about the primary prevention of diabetes are needed that may help to restrain the growing burden of diabetes [
2].
We targeted community-based educational interventions. It is now well-established that the health education of the public is a cardinal tool for both disease prevention and health promotion [
7]. This is concordant with the findings of this study where diabetes incidence reduced by 46.0% overall. Health education works by bringing changes at both the cognitive, affective, and behavioral level [
7] that may aid in disease prevention and control. The effect of educational interventions was more profound on FBS than A1c (Figs.
2 and
3). This lack of adequate reduction in A1c could be related to methodological aspects (e.g., inadequate power). For example, while the number of studies and sample size for FBS was 11 and 11,578, these were 6 and 6,416 in case of A1c (Supple file
2). Also, the smaller improvement in A1c could be related to the fact that the participants could be more acquainted with normal glucose level than A1c. The other factors associated with A1c may include possible genetic determination of A1c [
5,
6] than FBS [
40]. Also, A1c thresholds are not uniform worldwide, and the sensitivity of these thresholds differ in different racial groups [
41,
42]. There are also different laboratory assay methods that may affect the measurement accuracy of A1c [
43]. Moreover, A1c levels differ with iron-deficiency anemia [
44], a factor with a varying frequency between populations. Accumulating evidence also suggest preventive impact of doing yoga in high-risk populations i.e. those with pre-diabetes and/or metabolic syndrome [
28].
Besides FBS and A1c, the favorable impact of educational interventions was noted in waist circumference and BMI (Fig.
2), which means that the participants changed in central obesity [
45]. This is a good outcome because waist circumference is a better predictor of the development of diabetes than BMI [
46]. The maximum change was noted in a study that implemented educational intervention through community health workers (Fig.
2d). It is logical to expect a higher probability of success in educational interventions if necessary social support, communication, monitoring and feed back to patients are provided by the intervener(s) [
47]. The identified educational interventions in this study have not indicated a significant effect on sBP and dBP probably because of the age range of participants and therefore, not considering them to be hypertensive or being at risk of high blood pressure in the conducted studies. Insignificant association of the implemented educational interventions and BP levels could perhaps be related to the applied methodology (e.g., undesirable statistical power) rather than an incongruence effect. However, others have shown that individuals may have an extremely poor attitude towards BP control, which needs to be scrutinized in separate independent interventions. For example, the prescribed therapeutic regimens are believed by some people to prohibit life’s pleasure and control personal liberty or freedom of choice [
48,
49].
Subgroup analyses
We performed various subgroup analyses with regards to the effect of interventions on FBS vis-à-vis the duration of follow-up, gender, age, and theoretical framework (Figs.
1,
2,
3). There was no association of the duration of follow-up with the change in FBS levels. These results may perhaps be related to the degree of attendance or intensity of intervention sessions. For instance, the studies with a longer follow-up showed a lower reduction in FBS, which could be related to pathophysiological progression toward diabetes; perhaps meaning that the suitability of educational interventions may vary with the pathophysiological progression towards the development of diabetes [
30]. The longer programs have other impediments such as competing demands at home, not adequately motivated, no accompanying companion, and environmental factors such as bad weather. Others have also shown that the benefits of physical activity interventions decrease with longer follow-up [
50].
We found that the use of theoretical framework-based interventions brought more favorable changes in FBS levels. These results are not different from what we and others [
16] anticipate that theories may provide a better model-fit with diabetes prevention [
16]. However, in contrast to the theory-based paradigm, others have been seemingly critical of the effectiveness of theory-based interventions [
51]. But, that is because the data supporting theory-based paradigms are not adequate yet, and even their conclusions are limited by methodological and reporting issues [
52]. We agree with the reasoning of the current lack of adequate data as only a few (
n = 8, 40.0%) studies had a predefined theoretical framework for their intervention in our study. Studies without a theoretical framework had also shown their effectiveness in reducing diabetes risk parameters in our study. However, the possibility of better effectiveness with theory-based interventions remains open until adequate newer data becomes available.
We found that only 19 of 8181 studies had looked at health education as their intervention for the reduction of diabetes risk parameters. Even more unfortunate was the fact that the majority (
n = 12, 63.1%) of these studies were conducted in merely three high-income countries. From our region, we found only one study conducted in our country, thereby leaving aside most of the other countries. Thus, there is no surprise that the goal of reducing the burden of diabetes remains lagged [
53]. In terms of bibliometric efficiency, it is also noteworthy that only 19 studies were obtained from 8181 studies (0.2%), which shows a misfit rate of 99.7% (Fig.
1 and suppl file
1). So, from these results, one may surmise that databases are a cumbersome and imprecise source of literature, leading to unwarranted loss of precious time and labor. The associated reasons could perhaps be poor indexing since index terms and search keywords were carefully selected after a limited search of MEDLINE and EMBASE.
Although the effects were non-significant, FBS was found to be decreased more prominently for men than women (Fig.
3b). There can be numerous reasons for this difference. For example, the most prominent risk factor of diabetes is obesity, which is more common in women [
10]. After that, there are diversities in biology, epigenetic mechanisms, culture, nutrition, lifestyle, environment, and socioeconomic status. Each of these may distinctively impact the differences in predisposition, development, and clinical presentation of diabetes between men and women. Furthermore, sex hormones have a great impact on energy metabolism, body composition, vascular function, and inflammatory responses, and women may have more unfavorable cardio-metabolic traits [
11].
Publication bias and heterogeneity
We found no indication of publication bias in our study. We detected heterogeneity, but that may only become evident after the data collection and analysis. For this reason, we used the random-effects analysis, which in part accounts for the heterogeneity between studies. However, being stricter with the inclusion criteria would have eliminated most of the studies, like those with a particular theoretical framework. Each research team prefers to use their ways to develop and report interventions [
54].
Limitations
Our work has some limitations. First, our study is post hoc, which means that we had to rely on the data that were available for us. Second, the number of studies was low; for instance, the number of published diabetes incidence studies was merely three, by the time of study search. This brings us to the necessary predicament that every health agency is interested in that the burden of diabetes reduces; yet, the effort is far from being the bare minimum for having the necessary fundamental epidemiological data on diabetes. Because of limits in available data, we could not compare the intended group analysis, such as between different theoretical frameworks. Third, we did not compare educational interventions with interventions for other kinds of diabetes. Fourth, heterogeneity was high, which is not unexpected. One way to reduce the heterogeneity between studies would be to use theoretical framework-based interventions that would then enhance the comparability between studies. Community-based educational interventions are often conducted under real-world conditions, so they are often with quasi-experimental designs and a high level of heterogeneity within samples [
18]. That is why we included studies with both randomized control/ pseudo-randomized designs. Fifth, we included English language studies after 2000 till 2020 only, and our study did not evaluate feasibility outside the study settings. Lastly, few studies were of low quality, which may have affected some of our results.
Conclusions and recommendations for research
Based on a comprehensive data collection of about 16,106 participants and reasonable analyses, we conclude that there is an acute paucity of reliable community-based educational interventions towards the prevention of diabetes from both high- and low-middle-income populations. Nevertheless, educational interventions may reduce diabetes incidence by 46.0%, particularly through effectuating a reduction in fasting blood glucose, body mass index, and waist circumference. The even more useful result is that diabetes risk parameters may reduce irrespective of the duration of follow-up, at as low as 6 months. Although both genders were found to experience a decline in diabetes risk parameters, men were most likely to benefit more than females. Such gender difference could be related to many possible reasons, including sex differences in diabetes or its risk factors across countries, diversity in epigenetic mechanisms, culture, lifestyle, sex hormones, body composition, vascular function, inflammatory responses, environment, and socioeconomic status between men and women. Finally, studies with theoretical framework-defined interventions were 58.0% more likely to effectuate favorable changes in diabetes risk parameters, particularly fasting blood glucose levels. Unfortunately, there is a lot left to discover and identify before we may eventually reach towards having efficacious and effective strategies for the prevention of diabetes. More research regarding sex-dimorphic pathophysiological mechanisms of T2DM and its complications could contribute to more personalized diabetes care in the future and would thus promote more awareness in terms of sex- and gender-specific risk factors.
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