Differences in homeostatic model assessment (HOMA) values and insulin levels after vitamin D supplementation in healthy men: a double-blind randomized controlled trial

Vitamin D is thought to play a role in glucose metabolism. The aim of the present study was to determine the effect of vitamin D supplementation on markers of insulin sensitivity and inflammation in men without diabetes with vitamin D deficiency/insufficiency. In this 1-year double-blind randomized controlled trial, 130 men aged 20–65 years (mean age 47.52 ± 11.84 years) with serum 25-hydroxyvitamin D levels <50 nmol/l (mean 38.89 ± 8.64 nmol/l) were randomized to treatment (100 000 IU vitamin D bimonthly) or placebo. Anthropometric measurements, demographic questionnaires, and blood indices (fasting glucose, insulin, high-sensitivity C-reactive protein, lipids) were collected and repeated after 6 and 12 months. The compliance rate was 98.5%. Multivariate models, adjusted for baseline levels, age, body mass index, sun exposure, physical activity and LDL, showed significant differences in insulin and homeostatic model assessment of insulin resistance (HOMA-IR) values between groups. Levels of insulin and HOMA-IR values remained steady during the study period in the treatment group but increased by 16% in the control group (p = 0.038 and p = 0.048, respectively). Vitamin D supplementation administered for 12 months in healthy men maintained insulin levels and HOMA-IR values relative to the increase in the control group. Further studies are needed to establish the long-term effect of vitamin D supplementation on the risk of diabetes.