Evidence Gap on the Prevalence of Non-conventional Risk Factors for Type 2 Diabetes in Iran
Article information
Abstract
Objectives
Robust scientific evidence exists about the role of non-conventional risk factors in type 2 diabetes worldwide. The current epidemiological pattern of the disease in Iran suggests a precipitating role for these non-conventional risk factors. This review was performed to examine the research evidence suggesting a higher prevalence of non-conventional type 2 diabetes risk factors in Iran.
Methods
MeSH keywords were applied to search several databases, including PUBMED, MEDLINE, AMED, EMBASE, Iran DOC, and the Scientific Information Database without a time limit from inception to September 2011. The quality of the non-interventional and population-based studies on Iranians included in these databases was assessed by the authors and any disagreement was resolved with consensus.
Results
The literature search yielded 1847 publications, of which 62 were included in this study after eliminating non-relevant and overlapping papers. No study was found that verified a higher prevalence of the non-conventional type 2 diabetes risk factors in the Iranian population.
Conclusion
The identified evidence gap about the role of prominent non-conventional risk factors of type 2 diabetes in the Iranian population could be a major caveat in the application of an evidence-based approach to endorse or reject existing hypothesis about these risk factors. Studies on the prevalence of non-conventional biomarkers of type 2 diabetes among Iranians could be a promising area of research.
1 Introduction
Type 2 diabetes is a highly prevalent metabolic disorder and accounts for about 90% of all cases of diabetes in the world [1]. The global prevalence of type 2 diabetes has reached 6.4%, which could be an overwhelming burden on the health and economies of countries [2]. Although there is robust scientific evidence about the role of conventional risk factors and, consequently, about effective preventive strategies to halt the progress of the disease worldwide, the marked increase in type 2 diabetes in recent decades represents a failure in putting the established science into practice [3].
The prevalence of type 2 diabetes among adult Iranians aged 25–64 years is estimated to be 7.7%, excluding undiagnosed patients [4]. Lifestyle changes, especially in urban areas, low rates of physical activity, and obesity are the main recognized conventional triggers in the occurrence of type 2 diabetes across the country [5]. The onset of the disease in Iran is currently mostly observable in the 45–55 year age group, whereas in the developed world it is mainly a disease of old age, i.e., over the age of 65 years [6]. Such a difference may be due to a higher prevalence of conventional and non-conventional type 2 diabetes risk factors in Iran.
Lower plasma creatinine [7], a high intake of total and animal protein [8], plasma apelin and visfatin levels [9,10], lower β-cell function [11], plasma preptin levels (a hormone that is co-secreted with insulin and amylin from the pancreatic β cells) [12], serum 25-hydroxyvitamin D (25OHD), and dietary calcium [13–16] are a group of non-conventional risk factors that may explain the higher incidence and prevalence of type 2 diabetes in some ethnic groups.
This study was performed to look at the empirical research evidence about the studied risk factors for type 2 diabetes in the Iranian population and to check whether there was any hypothesis to suggest a higher prevalence of non-conventional type 2 diabetes risk factors in Iran.
2 Materials and methods
In this systematic review, various keywords (including “type 2 diabetes”, “diabetes mellitus”, “maturity onset diabetes” or “noninsulin-dependent diabetes”, and “Iran” and “risk factor” with their Persian equivalents) were applied to search the PUBMED, MEDLINE, AMED, CINAHL, EMBASE, SCOPUS, and MEDLIB databases, and also the Scientific Information Database (SID; a national database of published articles in Iranian journals) and IRAN DOC (a database of published papers and thesis in Iran) without a time limit from inception to September 2011. The Super Searcher of Google Scholar was also checked for unpublished materials within the same time limit. All non-interventional population-based studies on Iranians living in Iran were included, but studies on people living in institutions, Iranians living abroad, and publications in non-English or non-Persian languages were excluded.
A customized data extraction sheet was used to extract and record the study data. The quality of the studies was determined based on the study design, sample size, sampling method, sampling frame, study feature, and a report of the type of conventional and non-conventional type 2 diabetes risk factors studied. The quality of the retrieved publications based on these quality criteria were assessed independently by the authors and any disagreement was resolved with consensus.
3 Results
We found 1836 publications in the first round of the search, along with 11 publications found through serendipitous discovery. The titles and abstracts of these identified publications were inspected and their relevance to the objective of this study was checked. As a result of overlaps among the scanned databases or inconsistencies with the study objectives, 1610 publications were excluded. Of the remaining publications (226), 150 papers were also excluded after they had been scrutinized in detail for inclusion and quality criteria. The full text of 76 publications were obtained at this stage and were studied thoroughly. Finally, 14 publications were excluded because they were not directly relevant to the study objectives. Consequently, 62 publications [17–74] were included in this review (Figure 1).

Flow diagram of the method of selecting publications on the risk factors of type 2 diabetes in Iran retrieved from databases.
The risk factor most often studied in the selected publications was obesity and waist circumference; the least studied risk factors were polycystic ovary syndrome and the use of specific types of drugs, such as phenytoin (Dilantin), diuretics (thiazides), corticosteroids, beta blockers, and steroids (contraceptives; Table 1).The applied cutoff points to assign abnormality in the retrieved studies are given in Table 2. Data about the year of publication of the included publications are given in Table 3.

Cutoff point applied to indicate a higher risk of type 2 diabetes in the Iranian studies retrieved from databases.

Year of the publication of the Iranian studies on the risk factors of type 2 diabetes retrieved from databases.
We found no study focused on the prevalence of non-conventional type 2 diabetes risk factors in the Iranian population, nor any hypothesis explaining a probable higher prevalence of non-conventional risk factors for type 2 diabetes.
4 Discussion
The findings of this study revealed a major gap in the study of prominent non-conventional risk factors for type 2 diabetes in the Iranian population. Obesity and waist circumference were among the most frequently studied risk factors that have been screened as predictors of type 2 diabetes in Iran. Inconsistency in the applied cutoff points of the studied risk factors compared with internationally agreed recommendations was noticeable in these studies [75]. To the best of our knowledge, this is the first systematic review investigating scientific evidence about the prevalence of non-conventional risk factors of type 2 diabetes in Iran. Although there is empirical research evidence suggesting that identified non-conventional type 2 diabetes risk factors might play a part in the incidence of the disease [76–78], no research evidence was identified to endorse or reject a higher prevalence of non-conventional type 2 diabetes risk factors in Iran. This should be considered as a major caveat in the application of an evidence-based approach in preventive and interventional programs to mitigate the burden of the disease.
Selection bias due to limited accessibility to all the relevant international databases, a lack of access to published work in Iran due to the absence of an integrated database of scientific publications, and inclusion criteria of selecting only publications in the English and Persian languages were major methodological sources of bias in this review. Therefore the study results must be considered with caution.
The findings of this study, regardless of the inherent limitations, highlight a major gap in studying the epidemiology of type 2 diabetes in Iran and demonstrated the inadequacy of scientific evidence to precisely explain the triggering factors for the epidemic in the country. The paucity of scientific evidence to inform the national type 2 diabetes care protocol may explain and even broaden the current identified gaps in the Iranian type 2 diabetes care protocol [79]. As a promising area of study, we invite researchers to work on the prevalence of the prevailing non-conventional type 2 diabetes biomarkers and also on any hypothetical non-identified biomarker that could potentially clarify whether any non-conventional type 2 diabetes risk factors may explain the current expanding pattern of the disease in Iran.
Conflicts of interest
The authors declare no competing or conflict of interests.
References
Acknowledgments
This study was funded by the Tabriz University of Medical Sciences (grant no. 5/53/3169) and was part of the thesis research project of A.A. for the MSPH degree in Health Education and Promotion.
Notes
This is an Open Access article distributed under the terms of the Creative Commons Attribution Non-Commercial License (http://creativecommons.org/licenses/by-nc/3.0) which permits unrestricted non-commercial use, distribution, and reproduction in any medium, provided the original work is properly cited.