The effect of 25-hydroxyvitamin D on insulin sensitivity in obesity: is it mediated via adiponectin?

There has been substantial recent interest in using vitamin D to improve insulin sensitivity and preventing/delaying diabetes in those at risk. There is little consensus on the physiological mechanisms and whether the association is direct or indirect through enhanced production of insulin-sensitising chemicals, including adiponectin. We examined cross-sectional associations between serum 25-hydroxyvitamin D (25(OH)D) and insulin sensitivity (Matsuda index), parathyroid hormone (PTH), waist circumference, body mass index (BMI), triglycerides (TG), total and high molecular weight (HMW) adiponectin, HMW : total adiponectin ratio (HMW : total adiponectin), and total cholesterol : HDL cholesterol ratio (TC:HDL cholesterol) in 137 Caucasian adults of mean age 43.3 ± 8.3 years and BMI 38.8 ± 6.9 kg/m(2). Total adiponectin (standardised β = 0.446; p < 0.001), waist circumference (standardised β = -0.216; p < 0.05), BMI (standardised β = -0.212; p < 0.05), and age (standardised β = -0.298; p < 0.001) were independently associated with insulin sensitivity. Serum 25(OH)D (standardised β = 0.114; p = 0.164) was not associated with insulin sensitivity, total or HMW adiponectin, HMW : total adiponectin, or lipids. Our results provide the novel finding that 25(OH)D is not associated with HMW adiponectin or HMW : total adiponectin in nondiabetic, obese adults and support the lack of association between 25(OH)D and lipids noted by others in similar groups of patients.