Prevalence of metabolic syndrome and its components in Iran: an updated meta-analysis

Abstract

Background

Considering, the changes in lifestyle during the last decade the main aim of this study was to investigate the pooled prevalence of metabolic syndrome (MetS) and its components in Iran.

Methods

For implementing a comprehensive search strategy related to the objectives of the present meta-analysis, all international databases like PubMed (Medline), Scopus, Embase, Web of Sciences (Elsevier), and CINHAL were searched up to January 2024. The quality of the final selected studies was evaluated according to the Joanna Briggs Institute Critical Appraisal (JBI) tool for analytical cross-sectional studies. The subgroup analysis was performed based on gender, province, area, criteria of diagnosis, and components of metabolic syndrome. All of the analyses were carried out in STATA version 17.

Results

Among 2,034 relevant primary studies, 194 articles were entered into the meta-analysis. the prevalence of MetS in Iran was assessed using various criteria. The overall pooled prevalence was (31%, 95% CI: 28–34%), with a higher occurrence in females and individuals aged over 65 years. The central region, particularly Qom, reported the highest prevalence, while Tehran had the lowest. Low HDL cholesterol and waist circumference were the most common MetS components. The study provides critical data for health policy and intervention strategies in Iran.

Conclusion

Higher rates in females and the elderly and the predominance of low HDL cholesterol and waist circumference as MetS components call for targeted public health interventions. These insights are pivotal for formulating strategic health policies to mitigate MetS and its impact on the Iranian population.

Introduction

Metabolic syndrome (MetS) and its equivalent terms, including syndrome X and insulin resistance syndrome, were first mentioned by Reaven in the 80s [1]. It is the simultaneous presence of the main physiological, biochemical, and metabolic risk factors that lead to the acceleration of the atherosclerosis process, and vascular endothelium damage and it significantly increases the risk of cardiovascular disease (CVD), type 2 diabetes mellitus (T2DM), stroke, myocardial infarction (MI), and mortality [2, 3]. Metabolic syndrome is characterized by insulin resistance, fatty acid accumulation, inflammation, and oxidative stress, clinically presenting as central obesity, hypertension, hyperglycemia, and atherogenic dyslipidemia with low HDL or high triglycerides [4, 5].

The most common criteria used to define MetS include the World Health Organization (WHO), the European Group for the Study of Insulin Resistance (EGIR), the National Cholesterol Education Program for the Treatment of Adults Panel (NCEP ATP III), the American Association of Specialists Clinical Endocrinology (AACE) and International Diabetes Federation (IDF), which have different parameters despite their many similarities [6]. Anthropometric differences between Iranians and other Asians led Iran’s Ministry of Health to establish the first Iranian criteria in 2009, modifying anthropometric cut-offs with the Research Institute for Endocrine Sciences, a WHO collaborative center [7]. The cut-off points were adjusted to better predict cardiovascular outcomes in Iranians, improving health assessments and interventions to fit their unique context [8].

The Islamic Republic of, Iran, in West Asia, has over 89 million people, about 1.11% of the world’s population, according to the latest United Nations data [9]. Iran’s population varies in demographic and genetic factors, affecting prevalence rates across regions [10]. According to the previous study, the prevalence of MetS among children and adolescents in the world in 2020 was about 3% and 5%, respectively, and this finding was also reported among Iranian adolescents at 9% [11].

A meta-analysis by K. K. Farmanfarma and colleagues found that the overall prevalence of metabolic syndrome (MetS) among Iranian adults from 2000 to 2016 was about 30.4%, with significant regional variations; Sistan and Baluchistan had the highest prevalence, while Bushehr had the lowest. The analysis highlighted higher rates of MetS in women and across various age groups [12]. Another study conducted from 2005 to 2016 also explored the prevalence of MetS in Iran, which reported 31% [13]. This analysis utilized various diagnostic criteria for metabolic syndrome (MetS) in Iran, including ATP III, IDF, and JIS, which may identify more at-risk individuals. Higher MetS rates are found among females, urban residents, and the elderly, with prevalence increasing with age [14].

The association of MetS with other diseases, such as non-alcoholic fatty liver disease (NAFLD), gallstones, and reproductive disorders, as well as the identification of underlying factors such as overweight and obesity, improper diet, and reduced physical activity, is the basis for creating preventive approaches to the title of the first line of treatment and overall therapeutic interventions included lifestyle modification, use of pharmaceutical agents and bariatric surgery to minimize complications and disease burden, screening and early diagnosis [13, 15, 16].

Due to lifestyle changes and the rise of non-communicable diseases over the past decade, effective screening and treatment are essential to reduce the burden of metabolic syndrome (MetS) in Iran. This prompted an updated systematic review of Fatahi et al. [17] to inform evidence-based policies for screening, prevention, risk assessment, identification, and intervention across diverse communities. Given MetS’ importance in cardiovascular diseases, original studies from 2016 onwards should examine additional objectives, including prevalence based on age groups, province, syndrome components, larger sample sizes, and modified methodology.

Methods

This study was based on the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines related to the systematic review and meta-analysis of observational studies [18]. The protocol of this review was registered in PROSPERO (CRD42023388568).

Study selection and eligibility criteria

Eligibility criteria for inclusion in the systematic review and meta-analysis were [1] cross-sectional studies whose main purpose was to determine the prevalence of MetS and its components in Iran without restrictions on the characteristics of the studied populations [2], the methods of diagnosing MetS according to the criteria definition (Table 1). [3], studies with a clear definition of MetS according to the above criteria. Exclusion criteria included case controls, cohorts, case reports, case series, reports, letters to the editor, clinical trials, and reviews. In an initial search of international databases, 2,034 relevant studies were identified. Upon removal of duplicates, 1,360 references were retained. Subsequent title and abstract evaluation led to the exclusion of 630 articles. Further screening of 310 articles based on full-text assessment was conducted. Ultimately, 194 cross-sectional studies that reported on the prevalence of metabolic syndrome were included in the meta-analysis. Also, conference papers were included however, they comprised a very small number of the total. (refer to Fig. 1).

Table 1 Criteria for diagnosis of metabolic syndrome

Fig. 1

Flow diagram of study selection process

Search strategy

All original articles published up to January 2024 in international databases including PubMed (Medline), Web of Sciences (Elsevier), Scopus, EMBASE, and CINHAL were searched without language restrictions to identify eligible studies based on the following main study keywords including “The Islamic Republic of Iran”, “Iran”, “MetS”, and their synonyms. Gray Literature was then searched to access unpublished articles and dissertations or international reports. We also utilized the ProQuest database to investigate theses related to the title under review. In addition, after the final selection of articles, a manual search was performed by reviewing the references of related articles. The search strategy in international databases was independently conducted by two researchers (AM and SA) and the disputes were resolved by a third person (YM). (full search strategy provided in Supplement 1.)

Data extraction

Eligible studies were thoroughly reviewed and the following information was extracted using a checklist that included author name, year of publication, study period and country, reference population, age, sex, sample size, diagnostic criteria for Metabolic syndrome, and reported prevalence (%) of its components. The search strategy in the international databases, the whole screening process, data extraction, and quality assessment were performed by two independent researchers (AM and SA), and any disagreements were resolved by a third person (YM). (extracted data provided in Supplement 2.)

Quality assessment

The methodological quality and risk of articles included in this study were evaluated by the Joanna Briggs Institute (JBI) critical appraisal checklist for cross-sectional studies [19], consisting of eight questions. JBI critical appraisal tools have been developed by the JBI and collaborators and approved by the JBI Scientific Committee following an extensive peer review. The purpose of these appraisals is to assess and measure statistical analyses, inclusion criteria, confounding factors, exposure, and outcomes by the terms of ‘Yes’, ‘No’, ‘Not Applicable’, and ‘Unclear’. (Table 2).

Table 2 Quality assessment of included studies

Statistical analysis

According to the study checklist, the frequency of all sample sizes and patients with metabolic syndrome in each study was extracted. Then, based on the extracted information, the Metaprop and Metan command was used to calculate the pooled prevalence. The random effect model (REM) was also used for analyses. Cochran’s Q and I² tests were used to check the heterogeneity and variance of the studies selected for meta-analysis. The following cut-off percentages are commonly accepted: Low heterogeneity: I² values from 0 to 25%, Moderate heterogeneity: 26–75%, and High heterogeneity: I² values greater than 75% [20]. Subgroup analyses were performed based on sex, province, region, diagnostic criteria, and components of the MetS. The provinces of Iran were divided into four regions based on a combination of geography and socioeconomic status (SES), such as years of education, employment rates, and family wealth [21]. To analyze the data, the STATA 17 software was used, considering the confidence level of 95%. For data analysis, we integrated the findings from both the ATP III and its modified counterpart. Similarly, the reports from the IDF and the Iranian-modified IDF were merged. Additional criteria analyzed included those established by the American Heart Association (AHA) and the National Heart, Lung, and Blood Institute (NHLBI), as well as the WHO, Iranian criteria, and the Joint Interim Statement (JIS).

Results

These studies spanned from 1992 to 2024, encompassing a total of 526,562 individuals, with 241,222 males, 262,082 females, and 23,258 individuals of unspecified gender. The research was distributed across 31 provinces, The number of studies conducted in each Iranian province varied, with Tehran hosting the most at 52 studies, followed by Isfahan (28), Fars (22), Mazandaran (18), and Razavi Khorasan (17), while the other provinces had fewer studies, ranging from 6 to 13 each. Forest plots and funnel plots were also reported based on the diagnostic criteria for metabolic syndrome. (Supplement 3–8.)

NCEP ATP III criteria

In a comprehensive analysis across 15 provinces in Iran, the overall pooled prevalence of MetS was (31%, 95% CI: 28–34%). Notably, MetS was more prevalent in females ( 36%, 95% CI: 30–42%) compared to males ( 25%, 95% CI: 22–28%). Most studies focused on individuals aged 30–65 years, while one study highlighted a high prevalence among those aged > 65 years ( 42%, 95% CI: 38–46%). The analysis by the health status of the studied population indicates that among healthy individuals or those not reported, the prevalence was (26%, 95% CI: 24 − 28%). In contrast, 3 studies on diabetes mellitus showed a strikingly high prevalence of (76%, 95% CI: 56 − 91%), while those with polycystic ovary syndrome (PCOS) had a prevalence of (15%, 95% CI: 7 − 26%). Additionally, individuals with other diseases (Psychiatric, skin, cancer, and blood diseases) exhibited a prevalence of (41%, 95% CI: 32 − 50%). The central region of Iran was the primary research focus, with one study in Qom reporting the highest prevalence (73%, 95% CI: 67–79%). Conversely, the lowest prevalence was observed in two studies conducted in Sistan and Baluchistan (19%, 95% CI: 18–21%). Among the MetS components, waist circumference and low HDL cholesterol exhibited the highest prevalence, while elevated fasting blood glucose had the lowest prevalence (31%, 95% CI: 26–36%). These findings provide valuable insights for evidence-based decision-making and health policy formulation. Details related to this criterion are presented in Table 3. A Geographic Information System (GIS) related to this criterion has been provided at the provincial level in Iran. (Fig. 2.)

Table 3 Prevalence of metabolic syndrome in Iran based on NCEP ATP III criteria

Fig. 2

Prevalence of metabolic syndrome based on NCEP ATP III criteria in Iran using the geographic information system (GIS)

IDF criteria

In a comprehensive analysis across 15 provinces in Iran, the overall pooled prevalence of MetS was 31% (95% CI: 28–34%). Notably, MetS was more prevalent in females (36%, 95% CI: 30–42%) compared to males (25%, 95% CI: 22–28%). Most studies focused on individuals aged 30–65 years, while one study highlighted a high prevalence among those aged > 65 years (42%, 95% CI: 38–46%). Looking at health status, healthy individuals or those not reported had a prevalence (29%, 95% CI: 26 − 33%), whereas individuals with diabetes mellitus showed a significantly high prevalence (79%, 95% CI: 77 − 82%). Those with other diseases had a prevalence of 30% (95% CI: 13 − 51%). The central region of Iran was the primary research focus, with one study in Qom reporting the highest prevalence (73%, 95% CI: 67–79%). Conversely, the lowest prevalence was observed in two studies conducted in Sistan and Baluchistan (19%, 95% CI: 18–21%). Among the MetS components, waist circumference and low HDL cholesterol exhibited the highest prevalence, while elevated fasting blood glucose had the lowest prevalence (31%, 95% CI: 26–36%). These findings provide valuable insights for evidence-based decision-making and health policy formulation. Data associated with these parameters are compiled in Table 4. And GIS-based maps across Iran’s provinces (Fig. 3.).

Table 4 Prevalence of metabolic syndrome in Iran based on IDF criteria

Fig. 3

Prevalence of metabolic syndrome based on IDF criteria in Iran using the geographic information system (GIS)

AHA/NHLBI criteria

An aggregate of 18 studies assessing MetS in Iran found a total prevalence of (32%, 95% CI: 26–39%), with a higher incidence in females (41%, 95% CI: 30–52%) compared to males (31%, 95% CI: 25–38%), and the highest prevalence of MetS components was in low HDL cholesterol, contrasting with the lowest in raised fasting blood glucose levels. Regarding health status, healthy individuals or those not reported had a prevalence of 29% (95% CI: 24 − 35%), whereas individuals with diabetes mellitus presented a significantly higher prevalence (80%, 95% CI: 78 − 82%). Those with other diseases show a prevalence of 36% (95% CI: 26 − 46%). In the central region of Iran, a meta-analysis revealed that Qazvin province had a MetS prevalence of (32%, 95% CI: 29–35%), while Tehran province reported the lowest at (5%, 95% CI: 4–6%); across studies, low HDL cholesterol levels were most prevalent, with raised fasting blood glucose levels being the least common component of MetS. Details related to this criterion are presented in Table 5.

Table 5 Prevalence of metabolic syndrome in Iran based on AHA/NHLBI criteria

Iranian criteria

Four studies utilizing Iranian criteria reported a MetS prevalence of (28%, 95% CI: 21–36%), predominantly in males aged 30–65 years, with low HDL cholesterol being the most prevalent component at (55%, 95% CI: 52–58%), followed by waist circumference. Subgroup analysis by province was not feasible due to data limitations. Details related to this criterion are presented in Table 6.

Table 6 Prevalence of Metabolic Syndrome in Iran based on Iranian Criteria

WHO criteria

Seven studies assessing MetS in Iran reported an overall prevalence of (25%, 95% CI: 19–31%), with similar rates in both genders; individuals over 65 years showed a higher prevalence (42%, 95% CI: 38–46%) compared to younger age groups, and Tehran had the most studies and highest prevalence among the central and western regions analyzed. Details related to this criterion are presented in Table 7.

Table 7 Prevalence of metabolic syndrome in Iran based on WHO criteria

JIS criteria

An analysis of 11 studies on MetS in Iran found an overall prevalence of (37%, 95% CI: 28–47%), predominantly in males aged 30–65 years, with the highest component prevalence in low HDL cholesterol, especially in Yazd province at (70%, 95% CI: 65–74%). Related data is shown in Table 8.

Table 8 Prevalence of metabolic syndrome in Iran based on JIS criteria

Other criteria

Other studies including 7 investigated the prevalence of MetS based on other criteria including EGIR, AACE, De Ferranti (used primarily for children and adolescents), and INCO (Iranian National Committee on Obesity). Related data is presented in Table 9.

Table 9 Prevalence of metabolic syndrome in Iran based on other criteria’s

Discussion

MetS, a cluster of conditions that increase the risk of heart disease, stroke, and diabetes, has been a growing concern worldwide. The global prevalence of MetS is estimated to be 20–25% in the adult population based on IDF criteria [22]. In Iran, the prevalence of this syndrome is particularly alarming due to various lifestyle and genetic factors. The higher prevalence in women based on AHA/NHLBI, NCEP ATP III, and IDF criteria could be due to various factors, including lifestyle, hormonal differences, and genetic predispositions. The increasing trend over time calls for effective prevention programs to address this growing health issue. Recent studies have shown that the prevalence of MetS in Iran varies depending on the diagnostic criteria used. According to the results, the prevalence rates based on different criteria range from 25 to 41% which was higher than the previous meta-analysis that reported a pooled prevalence of 0.26% and an incidence rate of 97.96 per 10,001. The previous meta-analysis found the highest and lowest prevalence of MetS using the Iranian definition criteria and the NHANES III, respectively (0.43 vs. 0.12). The recent analysis also indicates variability in prevalence based on different criteria, with the highest prevalence reported using the JIS criteria at 37%. This indicates that a significant portion of the adult population is at risk of non-communicable diseases (NCDs) associated with MetS. A comprehensive nationwide study conducted in 2016 utilized various criteria to estimate the prevalence rates of MetS among adults over 25 years. The findings revealed that the national prevalence rate of MetS ranged from 32.0 to 47.6%, depending on the definition criteria used [14].

Another systematic review and meta-analysis reported that the prevalence of MetS among cardiovascular patients in Iran was 34.2%, with the highest prevalence noted in studies conducted between 2015 and 2020 [23]. This suggests a rising trend in MetS, which could be attributed to changing dietary habits, sedentary lifestyles, and increased urbanization. Complications stemming from MetS include atherosclerosis, heart attacks, strokes, and type 2 diabetes, all of which can lead to increased healthcare costs and a need for more extensive medical infrastructure. Politically, the syndrome challenges healthcare systems to adapt and provide effective prevention and treatment strategies, which may include policy changes, public health campaigns, and resource allocation to manage this growing health concern.

The study highlights the concerning prevalence of metabolic syndrome (MetS) in Iran, particularly among females and individuals aged over 65, which is consistent with global trends indicating increased risk with aging. This situation poses a significant burden on the healthcare system and underscores the need for early screening and intervention strategies. Research indicates that the prevalence of MetS among children aged 10–19 years was reported at 9.5% based on ATP criteria and 5.8% according to IDF criteria in a study by Chiti et al. [24] (2005–2008). A global burden study by Noubiap et al. [25] (2021) found prevalence rates of 8.8% in children and 9.0% in adolescents. In adults, Soofi et al. [26] reported a prevalence range of 33–52% in the Ravansar cohort, with a notable increase among those aged 35–65 years based on IDF criteria. Jahangiry et al. [27] (2014) observed a progressive increase in MetS prevalence with age, particularly among participants aged 50–59, while those over 70 showed a lower prevalence.

The prevalence of MetS in Iran varies significantly based on health status, as evidenced by multiple studies using different criteria. These findings highlight the significant impact of diabetes on the prevalence of MetS and underline the importance of targeted interventions for at-risk populations. The findings are consistent with other studies in the same field. For instance, in a study conducted in Jangrabani et al. [28], a prevalence rate of 65% was reported. Evidence suggests that insulin resistance is the likely link between PCOS and metabolic syndrome [29]. Apridonidze et al. [30] reported a prevalence of MetS of 43% among women with PCOS. This finding underscores the increased risk of metabolic complications in women with PCOS compared to the general population. This finding underscores the increased risk of metabolic complications in women with PCOS compared to the general population.

The observed gender disparity in the prevalence of metabolic syndrome (MetS) aligns with previous meta-analyses, which report rates of 0.34 in women compared to 0.22 in men. This suggests that women may be more susceptible to MetS or its components due to various biological, behavioral, or socio-cultural factors. Specifically, the prevalence of MetS in Iranian women is approximately 1.3 to 1.4 times higher than in men according to AHA/NHLBI, ATP III NCEP, and IDF criteria. In contrast, the JIS, Iranian, and WHO criteria indicate a higher prevalence in men, estimated at 1.07 to 1.24 times greater than in women. Fatahi et al. reported a prevalence of 34% in women versus 22% in men, while Ghorbani et al. [31] found a prevalence of 37.8% in women compared to 17% in men based on ATP III criteria, and 44.1% in women versus 25.4% in men according to IDF criteria. Additionally, Esmailzadehha et al. [32] reported a prevalence of 30.5% in men versus 25.7% in women based on WHO criteria in a 2010–2011 study in Ghazvin.

The two most prevalent components of MetS in the Iranian population are reduced HDL cholesterol levels and central obesity. These concerning rates highlight the urgent need for effective management and prevention strategies, which should include lifestyle modifications, medical interventions, and public education on NCD risk factors. Interestingly, elevated fasting blood glucose, a critical indicator of diabetes risk, exhibits the lowest prevalence among MetS components, suggesting either successful diabetes prevention strategies or a delayed onset of hyperglycemia compared to other components. A meta-analysis by Ostovar et al. [33] found that the prevalence rates for MetS components based on ATP criteria in adults included high waist circumference (41%), high triglycerides (TG) (54%), low HDL (54%), high blood pressure (BP) (38%), and impaired fasting glucose (IFG) (22%). Additionally, a decade-long meta-analysis by Mazloomzadeh et al. [34] (2002–2012) reported low HDL cholesterol at 59.7%, hypertriglyceridemia at 39.5%, central obesity at 38.9%, hypertension at 25.9%, and IFG at 16.5%, further emphasizing the critical need for targeted public health interventions to address these prevalent risk factors in the Iranian population.

Urban areas in Iran, particularly Qom, exhibit a significantly higher prevalence of metabolic syndrome (MetS), indicating regional variations that may stem from differences in lifestyle, diet, or access to healthcare services. This necessitates targeted interventions to address the elevated prevalence rates observed in these regions. In contrast, provinces such as Sistan and Baluchistan show lower prevalence rates, which may reflect variations in ethnic backgrounds, environmental factors, or underdiagnosis due to limited healthcare resources. Notably, provinces like Bushehr, Yazd, and Kerman report very high prevalence rates, while Khuzestan, Semnan, and Fars have relatively lower rates. Fatahi et al. found a higher prevalence of MetS in urban areas, consistent with findings that suggest lifestyle differences between urban and rural populations contribute to this disparity. Dalvand et al. [13] reported prevalence rates of 45% in Hamedan and 9% in Ahvaz based on NCEP/ATPII criteria, and 65% in Kerman compared to 4% in Zanjan according to IDF criteria. Farmanfarma et al. [12] identified the lowest prevalence in Sistan and Baluchestan Province at 18.3% and the highest in Bushehr Province at 57.8%, further emphasizing the need for region-specific health strategies.

The rapid increase in MetS has been paralleled by the growing epidemic of type-2 diabetes, hypertension, cardiovascular disease, and obesity worldwide [35]. The impact of MetS on public health is profound. It significantly contributes to the burden of cardiovascular diseases, which are among the leading causes of death worldwide. A multi-faceted approach that includes public education on lifestyle modifications, medical interventions, and perhaps most importantly, a unified definition of MetS to streamline diagnosis and treatment strategies is needed. The economic implications are also substantial, as the management of chronic conditions associated with MetS requires long-term healthcare services. These findings have profound implications for health policy formulation in Iran.

We lacked precise information regarding the characteristics of the populations in the studies included in the meta-analysis, as many studies did not report demographic details concerning the presence of any underlying health conditions. Consequently, the categorization of the population in terms of health status was performed implicitly. Therefore, it is recommended that future primary studies in Iran be conducted with careful consideration of population characteristics, such as cohort studies with appropriate sample sizes. Future studies should explore the specific effects of various diseases on the prevalence and components of metabolic syndrome, and the underlying causes of the gender and age disparities in MetS prevalence. Research should also investigate the effectiveness of different intervention strategies across various regions and ethnic groups within Iran. Longitudinal studies could provide insights into the progression of MetS and the long-term outcomes of clinical interventions. Additionally, exploring genetic predispositions and environmental factors contributing to MetS in Iran could offer new avenues for prevention and treatment. The meta-analysis may have limitations due to the heterogeneity of the included studies, such as variations in the criteria used to define MetS and the age ranges of the populations studied [36]. The lack of data from all provinces and the potential underrepresentation of certain ethnic groups could limit the generalizability of the findings. Furthermore, most studies were cross-sectional, which limits the ability to infer causality between MetS and its risk factors.

Conclusion

The prevalence of MetS in Iran is alarmingly high, with significant gender, age, and regional disparities. These findings should catalyze the development of targeted health policies and interventions to mitigate the risk factors associated with MetS and reduce its burden on the Iranian healthcare system.