Association of Vitamin D, Parathyroid Hormone, and Insulin Resistance in Patients With Metabolic Syndrome: A Cross-Sectional Analytical Study

Background: Vitamin D and parathyroid hormone (PTH) have been linked to insulin resistance and metabolic syndrome(MetS), although their independent relationships remain uncertain. Materials and Methods: This cross-sectional analyticalstudy included 250 patients with MetS. Serum 25(OH) vitamin D, intact PTH (iPTH), and insulin resistance assessed byHOMA-IR were evaluated. Associations were examined using correlation analysis, subgroup comparisons and multivariableregression. Results: Vitamin D deficiency and insufficiency were present in 33.2% and 38.4% of participants, respectively.Serum 25(OH)D was inversely correlated with HOMA-IR, while iPTH was positively correlated with HOMA-IR. Vitamin Dand iPTH were inversely related. HOMA-IR increased significantly with greater MetS component burden. However, afteradjustment for age, sex, BMI, diabetes status, triglycerides, and HDL-C, neither vitamin D nor iPTH remainedindependently associated with HOMA-IR. BMI, type 2 diabetes, and triglycerides remained significant predictors.Conclusion: Vitamin D and iPTH showed crude associations with insulin resistance, but these were attenuated aftermetabolic adjustment, suggesting that adiposity and related metabolic abnormalities may be more important determinants ofinsulin resistance.