Introduction

Diabetes has emerged as a substantial global public health challenge in recent years, with the worldwide prevalence reaching 10.5% and projected to rise to 12.2% by 2045. The most notable increase in diabetes prevalence has been observed in middle-income countries [1, 2]. Both genetics and epigenetics play a significant role in the onset of diabetes and following clinical and daily life complications [3, 4]. The predictive efficacy of obesity-related variables for diabetes onset may vary across ethnicities, age groups, and genders, highlighting the role of both genetics and epigenetics in vulnerability to diabetes [5, 6].

Obesity poses a critical health threat, significantly increasing the risks of coronary heart disease, stroke, and type 2 diabetes mellitus (T2DM). However, body mass index (BMI) has been commonly used to evaluate weight status, but it inadequately assesses cardiometabolic risks in adults with excessive adiposity [7, 8]. In this regard, studies indicated that BMI, waist circumference (WC), and waist-to-hip ratio (WHR) anthropometric index are comparable in predicting diabetes onset and following complications [9, 10]. Moreover, patients with diabetes usually illustrated abnormalities in their laboratory findings [11, 12]. The WHR associated with fasting blood sugar (FBS) levels, proteomic profile, and lipid profiles reflect its role in assessing metabolic health. Studies have consistently demonstrated that individuals with disrupted anthropometric indicators often exhibit elevated FBS levels and, on the other side, diabetes associated with dyslipidemia [13, 14].

Moreover, a higher WHR is frequently correlated with adverse lipid profiles characterized by elevated levels of triglycerides (TG) and low-density lipoprotein (LDL) cholesterol and decreased levels of high-density lipoprotein (HDL) cholesterol [15, 16]. These lipid abnormalities contribute to a heightened risk of cardiovascular diseases among individuals with central adiposity, where WHR is a helpful predictor [17, 18]. Due to the importance of demographical and clinical risk factors associated with T2DM and the critical role of anthropometric indicators in the severity of the condition, by considering the limited studies on this issue in north Iran, the current study investigated the prevalence of T2DM and the relationship between WHR and diabetes in the Prospective Epidemiological Research Studies in Iran (PERSIAN) Guilan Cohort study (PGCS) population and the related risk factors.

Methods

Study design and participants

This cross-sectional study was derived from the data of the PERSIAN cohort study [19]. The study encompassed 10,520 individuals from the PGCS cohort, among whom 2,531 were diagnosed with diabetes and 7,989 were non-diabetic participants [20]. The demographical and clinical data, including age, gender, educational status, history of smoking, and hypertension were recorded. Anthropometric indicators, including weight (kg), height, hips, and WC, were measured according to the National Health and Nutrition Examination Manual [21]. BMI was reported as low weight (BMI < 18.5 kg/m2), average weight (BMI = 18.5–24.99 kg/m2), overweight (BMI = 25–29.9 kg/m2), and obese (BMI ≥ 30 kg/m2). WHR was calculated by dividing WC by hip circumference, and the normal level of WHR was evaluated as 0.9 or less in men and 0.85 or less in women.

The MET was used to assess the intensity of physical activity based on a standardized classification of the energy costs of different physical activities. MET was calculated using questionnaires given to the participants in face-to-face interviews by trained people to measure their activity intensity. The oxygen that was used during rest and immobility was equal to MET, and the participants were divided into four quartiles as sedentary, light, moderate, and high levels of physical activity according to daily activity levels by the number of hours of walking, working, exercise, etc. [19]. Hypertension was defined as a systolic blood pressure ≥ 140 mm Hg or a diastolic blood pressure ≥ 90 mm Hg [20].

The laboratory findings, including FBS, TG, LDL, and HDL, were analyzed via a Biotechnical auto-analyzer (BT 1500, Italy) at the medical laboratory of the PGCS center. Diabetes was definite as FBS ≥ 126 mg/dL and/or a history of diabetes diagnosis or use of anti-diabetic medications. Abnormal lipid profile was defined as follows: Chol ≥ 200 U/L, TG ≥ 150 U/L, LDL ≥ 100 U/L, and HDL ≤ 40 U/L [22].

Statistical analysis

Data was reported as mean ± standard deviation (SD) and number (percentage). The association between WHR and diabetes was analyzed using logistic regression analysis by odds ratio (OR) with a 95% confidence interval (CI). All data was analyzed using SPSS for Windows, version 16.0 (SPSS Inc., Chicago, IL, USA), and the significance level was set at 0.05.

Results

The mean age of participants was 51.52 ± 8.90 years. About 53.5% were female, 39.9% had normal BMI and 2531(24.1%) individuals had diabetes. A total number of 7628 (72.5%) people had abnormal WHR, of which 2072 (19.7%) people with diabetes and 5556 (52.8%) non-diabetics had abnormal WHR. Abnormal WHR was prevalent in most diabetic individuals aged over 50 and in most non-diabetic people under 50 (P > 0.05). In the diabetics group with abnormal WHR, 73.5% were females, and in non-diabetics, 70.7% of individuals with abnormal WHR were females. Most of the diabetic patients with abnormal WHR had abnormal levels of HDL and TG (71.0% and 72.0%, respectively), while the majority of non-diabetics had abnormal HDL (82.4%) (Table 1).

Table 1 Comparison of demographical and clinical data of diabetic and non-diabetic individuals with normal and abnormal WHR
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According to the logistic regression analysis, all participants over 50 had significantly higher abnormal WHRs than those under 50, P < 0.001. While females had abnormal WHR than males in both diabetic and non-diabetic groups, it was higher in the diabetic group (OR = 51.26, 95% CI: 30.11–87.30, vs. OR = 29.88, 95% CI: 24.22–36.85, P < 0.001), demonstrating the effect of gender on WHR. The chance of abnormal WHR increased with higher BMI levels in both groups (P < 0.05). Abnormal WHR in diabetic patients was significantly associated with lower LDL levels, whereas non-diabetic patients had higher LDL levels (P < 0.05). In none of the diabetic and non-diabetic groups, there was no statistically significant correlation with smoking, hypertension, HDL, and TG with abnormal WHR (P > 0.05) (Table 2).

Table 2 Logistic regression analysis for the Association between demographic and clinical factors among diabetic and non-diabetic individuals with normal and abnormal WHR
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Discussion

Increased body fat contributes to develo** metabolic disorders such as T2DM (23). Anthropometric indices measurement is a simple and non-invasive method used for obesity in therapeutic and epidemiological research [23, 24]. Therefore, the present study determined the association between WHR and diabetes. In this study, the prevalence of abnormal WHR in diabetics and non-diabetics was 81.8% and 69.5%, respectively. This finding aligns with other studies that indicate a high prevalence of abnormal obesity in humans [10, 25].

Additionally, most individuals with abnormal WHR were over 50 years old, consistent with the findings of Zhang et al., who confirmed that risk factors associated with diabetes include obesity and age 40 years and above [26]. Hadaegh et al. also found that a BMI of ≥ 30 kg/m2 and high WHR were predictors of type 2 diabetes among Iranians under 60 years old [27]. Therefore, age should be considered a confounding factor when using anthropometric measures to predict the risk of T2DM. De Hollander et al. demonstrated that an individual with a higher WC within the healthy weight category has a higher relative risk of mortality compared to an individual with the same WC in the overweight category [28].

Our results showed that females had a higher prevalence of abnormal WHR than males, and this proportion was more significant in individuals with diabetes compared to non-diabetics. Zhang et al. indicated that WC and WHtR are more effective in diagnosing diabetes in women over 40 compared to men [26]. This is likely due to gender differences in visceral fat accumulation and local adipose tissue distribution. Measuring sex hormones may provide further insights into this issue [6, 39]. Ali et al. indicated that older age and lower physical activity were significant determinants of general and abdominal obesity [40]. On the contrary, Gutierrez et al. suggested that the WHR and PP are unrelated in this group of military ambulatory hospitals. Contrary to expectations, only women with a higher or altered WHR and older adults aged 60–70 had an appropriate physical performance [41].

The current study showed that the risk of abnormal WHR was lower in diabetic patients with lower BMI. Feller et al. point out that the association between WC and the risk of T2DM was more robust with a low BMI than with a higher BMI [42]. Abdominal obesity is associated with elevated insulin concentrations in younger age groups and impaired glucose control in middle-aged groups [43]. Bala et al. reported that obesity is a risk factor for hemoglobin glycation. Therefore, it should be considered a measure for preventing prediabetes and diabetes [44]. We also found an inverse association between abnormal WHR in diabetics and LDL; no relationship was observed between HDL and TG. Controversially, Choi et al. found a significant positive association between WHR, total cholesterol, and LDL in diabetic men [45]. Sandhu et al. reported positive correlations between WHR, total cholesterol, LDL cholesterol, and TG in the 40–50 age group in diabetic men [46]. In diabetic individuals, the abnormal fat distribution and insulin resistance associated with an elevated WHR may uniquely impact lipid metabolism compared to non-diabetic individuals, leading to the observed differences in LDL cholesterol levels [45]. The current study reported valuable results from a large sample size through a cohort study on the association between diabetes and WHR. At the same time, its cross-sectional nature limited some real-time data.

Conclusion

The findings found that many participants had an abnormal WHR, particularly those with diabetes. Women, especially those with diabetes, had a higher chance of having an abnormal WHR. Being over 50 and having a higher BMI increases the likelihood of having an abnormal WHR. Diabetic patients often had abnormal levels of HDL and TG. These results highlighted how WHR can help assess metabolic health, especially in people with diabetes.