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.