Synergistic Impact of 25‐Hydroxyvitamin D Level and Obesity on the Risk of Metabolic Syndrome

Background: The global increase in the prevalence of metabolic syndrome (MetS), which is defined by impaired glucose homeostasis, visceral obesity, hypertension, and dyslipidemia, presents a significant health concern. Obesity is a primary risk factor for MetS, and low vitamin D levels have been linked to several metabolic disorders. Given the high prevalence of vitamin D deficiency among individuals with obesity, this study examined the combined influence of vitamin D deficiency and obesity on the risk of MetS. Methods: This cross‐sectional study was conducted from January 2021 to December 2022 at Shin Kong Memorial Hospital. A total of 7248 participants underwent physical examinations, including measurements of fasting glucose levels, lipid profiles, and serum 25‐hydroxyvitamin D levels. Participants were categorized into six groups according to vitamin D status (deficiency < 50 nmol/L, insufficiency 50–74.9 nmol/L, and sufficiency ≥ 75 nmol/L) and body mass index (BMI; nonobese < 27 kg/m 2 and obese ≥ 27 kg/m 2 ). Results: Vitamin D levels were significantly lower in younger patients, women, those with BMI ≥ 27 kg/m 2 , and those who engaged in exercise less frequently. Patients with vitamin D sufficiency and without obesity constituted the reference group. Vitamin D level was inversely associated with MetS (odds ratio [OR] = 1.7 and 95% confidence interval [CI]: 1.4–2.0), with a stronger association in individuals with obesity (OR = 9.2 and 95% CI: 7.9–10.7). The highest risk was observed in patients with both vitamin D deficiency and obesity (OR = 13.7). Vitamin D deficiency and obesity were found to synergistically influence MetS (synergy index: 1.3 and 95% CI: 1.0–1.7). Notably, the association between vitamin D deficiency and MetS was nonsignificant in patients without obesity. Conclusions: Both vitamin D deficiency and obesity are independently associated with MetS, with a synergistic effect observed when both conditions are present.