European Journal of Cardiovascular Medicine

Vitamin D, a fat-soluble secosteroid hormone, plays a critical role in calcium homeostasis and bone metabolism. However, beyond its classical functions, vitamin D is increasingly recognized for its influence on a wide array of physiological processes, including immune modulation, insulin sensitivity, and cardiovascular health (1). The biologically active form, 1,25-dihydroxyvitamin D, interacts with vitamin D receptors found in multiple tissues, suggesting its systemic importance (2).

Vitamin D deficiency is a global health concern, affecting nearly one billion people worldwide, with particularly high prevalence in urban populations due to lifestyle factors such as limited sun exposure, indoor occupations, and poor dietary intake (3,4). In India, several urban studies have reported deficiency rates ranging from 50% to 90%, even in regions with adequate sunlight, indicating a growing public health issue (5).

Metabolic syndrome (MetS) is a cluster of interrelated metabolic abnormalities, including abdominal obesity, hypertension, hyperglycemia, hypertriglyceridemia, and reduced HDL cholesterol levels. It significantly increases the risk of cardiovascular disease and type 2 diabetes (6). The pathophysiology of MetS involves chronic inflammation, oxidative stress, and insulin resistance—all mechanisms in which vitamin D is believed to play a regulatory role (7,8).

Recent studies suggest a potential inverse association between serum 25-hydroxyvitamin D [25(OH)D] concentrations and the risk of MetS, with several mechanisms proposed, including modulation of insulin secretion and sensitivity, suppression of the renin-angiotensin system, and reduction in systemic inflammation (9,10). However, findings across different populations remain inconsistent, and evidence from Indian urban settings remains limited.

Given the growing burden of both vitamin D deficiency and metabolic syndrome in urban India, this study aims to evaluate the prevalence of vitamin D deficiency and examine its association with metabolic syndrome among adults residing in an urban community.

Study Design and Participants:
A community-based cross-sectional study was conducted over a period of six months in an urban area. A total of 200 adults aged between 25 and 60 years were enrolled using a stratified random sampling technique to ensure age and gender representation. Participants with known liver, kidney, or parathyroid disorders, those on vitamin D supplementation, or with chronic illnesses such as cancer or autoimmune diseases were excluded from the study.

Data Collection and Measurements:
Each participant underwent a detailed clinical assessment including demographic data, medical history, and lifestyle factors such as physical activity and sun exposure. Anthropometric measurements including weight, height, waist circumference, and body mass index (BMI) were recorded using standardized methods. Blood pressure was measured in a seated position using a calibrated digital sphygmomanometer, and the average of two readings was used for analysis.

Laboratory Investigations:
Fasting blood samples were collected in the morning after an overnight fast of at least 8 hours. Serum was separated and stored at −20°C until analysis. Serum 25-hydroxyvitamin D [25(OH)D] levels were measured using a chemiluminescent immunoassay method. Fasting plasma glucose, triglycerides, and HDL cholesterol were analyzed using an automated clinical chemistry analyzer with standard enzymatic techniques.

Vitamin D status was categorized as follows:

• Sufficient: ≥30 ng/mL
• Insufficient: 20–29 ng/mL
• Deficient: <20 ng/mL

Metabolic syndrome was diagnosed according to the NCEP ATP III criteria, which require the presence of at least three of the following components:

1. Waist circumference ≥90 cm for men or ≥80 cm for women
2. Triglycerides ≥150 mg/dL
3. HDL cholesterol <40 mg/dL for men or <50 mg/dL for women
4. Blood pressure ≥130/85 mmHg
5. Fasting glucose ≥100 mg/dL

Statistical Analysis:
Data analysis was performed using SPSS version 26.0 (IBM Corp., Armonk, NY). Continuous variables were expressed as mean ± standard deviation (SD) and categorical variables as percentages. The chi-square test was used to assess associations between categorical variables. Logistic regression analysis was performed to determine the independent association between vitamin D deficiency and metabolic syndrome, adjusting for age, gender, and BMI. A p-value of <0.05 was considered statistically significant.

A total of 200 urban adults participated in the study, comprising 108 females (54%) and 92 males (46%) with a mean age of 42.7 ± 9.4 years. Based on serum 25(OH)D levels, 124 participants (62%) were categorized as vitamin D deficient (<20 ng/mL), 48 (24%) as insufficient (20–29 ng/mL), and 28 (14%) as sufficient (≥30 ng/mL).

Metabolic syndrome was identified in 76 participants (38%) using the NCEP ATP III criteria. The highest prevalence of metabolic syndrome (49.2%) was observed among those with vitamin D deficiency, while only 17.8% of participants with sufficient vitamin D had metabolic syndrome (p < 0.01) (Table 1).

Logistic regression analysis revealed that individuals with vitamin D deficiency had significantly higher odds of having metabolic syndrome (OR: 2.71; 95% CI: 1.44–5.32; p = 0.003) compared to those with sufficient levels, even after adjusting for confounding variables like age, sex, and BMI (Table 2).

Table 1. Prevalence of Metabolic Syndrome According to Vitamin D Status

Table 2. Logistic Regression Analysis of Vitamin D Deficiency and Risk of Metabolic Syndrome

As shown in Table 1, the occurrence of metabolic syndrome increased significantly among individuals with lower vitamin D levels. Furthermore, Table 2 demonstrates that vitamin D deficiency remained an independent predictor of metabolic syndrome after adjusting for potential confounders.

The findings of this study demonstrate a high prevalence of vitamin D deficiency among urban adults and reveal a significant association between low vitamin D levels and the presence of metabolic syndrome. These results are in line with previous reports suggesting that vitamin D deficiency is a widespread health issue, particularly in urban populations where sedentary lifestyles and limited sun exposure are common contributing factors (1,2).

The prevalence of vitamin D deficiency in our study (62%) is consistent with earlier studies conducted in Indian urban settings, which have reported similar rates ranging from 50% to over 80% (3,4). Several factors contribute to this trend, including indoor occupations, air pollution blocking ultraviolet B radiation, and cultural practices that limit skin exposure to sunlight (5,6).

Metabolic syndrome, a condition characterized by central obesity, insulin resistance, hypertension, and dyslipidemia, was observed in 38% of the participants. This aligns with estimates from recent urban epidemiological surveys indicating a rising burden of metabolic disorders in Indian cities (7,8). The significant correlation found between vitamin D deficiency and metabolic syndrome in our study supports the hypothesis that vitamin D plays a role in modulating metabolic health.

Vitamin D is thought to influence metabolic syndrome through multiple mechanisms. It improves insulin sensitivity by regulating calcium flux in pancreatic β-cells and peripheral tissues and modulates inflammatory responses, both of which are critical in the pathogenesis of metabolic syndrome (9,10). Furthermore, vitamin D suppresses the renin-angiotensin-aldosterone system, which may contribute to its protective effect against hypertension (11).

Several studies have reported inverse associations between serum 25(OH)D levels and various components of metabolic syndrome. For instance, a study by Ford et al. in the U.S. adult population found that lower vitamin D levels were associated with higher fasting glucose and blood pressure (12). Similarly, a meta-analysis by Yin et al. showed that vitamin D deficiency was linked to an increased risk of developing metabolic syndrome (13).

While the observational nature of this study limits the ability to establish causality, the association remained significant even after adjusting for key confounders such as age, sex, and BMI. These findings are consistent with those of the Tromsø Study, which identified a dose-dependent relationship between vitamin D levels and the risk of metabolic syndrome after multivariate adjustment (14).

Nonetheless, it is important to acknowledge the limitations of this study. The cross-sectional design restricts the interpretation of temporal relationships. Dietary intake of vitamin D and physical activity were not quantitatively assessed, which may confound the observed associations. Future longitudinal studies and randomized controlled trials are needed to clarify the causal role of vitamin D in the pathogenesis and management of metabolic syndrome (15).

This study identified a high prevalence of vitamin D deficiency among urban adults and demonstrated a significant association between low vitamin D levels and the presence of metabolic syndrome. These findings suggest that monitoring and correcting vitamin D deficiency may help reduce the burden of metabolic syndrome and its associated health risks in urban populations.

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