Possible Role of Hyperinsulinemia and Insulin Resistance in Lower Vitamin D Levels in Overweight and Obese Patients

A cohort of 66 healthy overweight and obese patients, 53 women and 13 men were examined. Waist circumference and fasting 25(OH)D, insulin, glucose, lipid (cholesterol, HDL cholesterol, and triglyceride), C-reactive protein (CRP), and complement 3 (C-3), and 4 (C-4) serum concentrations were measured. Insulin resistance was assessed by the homeostasis model assessment (HOMA(IR)). Results. 25(OH)D levels showed a significant negative correlation with BMI (P < 0.01), waist circumference (P < 0.05), fasting insulin (P < 0.01), HOMA(IR) (P < 0.01), triglycerides (P < 0.01), CRP (P < 0.01), C3 (P < 0.05), and C-4 (P < 0.05). Multiple regression analyses were performed with 25(OH)D as the dependent variable and BMI (or waist circumferences), fasting insulin (or HOMA(IR)), triglycerides, and CRP (or C-3 or C-4) as independent variables. Only insulin or HOMA(IR) maintained a significant independent association with 25(OH)D levels, whereas vitamin D did not maintain a significant independent association with CRP or C-3 or C-4 concentrations. Conclusions.. e present study, performed in overweight and obese subjects, shows that 25(OH)D levels are negatively associated with inflammatory parameters such as CRP and C-3 and C-4 levels, but not independently of BMI, body fat distribution, insulin levels, or insulin resistance. Our results suggest that hyperinsulinemia and/or insulin resistance are directly responsible for decrease of 25(OH)D levels in obesity.