AIM: To determine the short-term effect of vitamin D(3) supplementation on insulin sensitivity in apparently healthy, middle-aged, centrally obese men.

SUBJECTS AND METHODS: A double-blind randomized controlled trial was conducted at a tertiary care facility in which 100 male volunteers aged > or = 35 years received three doses of vitamin D(3) (120,000 IU each; supplemented group) fortnightly or placebo (control group). Hepatic fasting insulin sensitivity [homeostasis model assessment (HOMA), quantitative insulin-sensitivity check index, HOMA-2], postprandial insulin sensitivity [oral glucose insulin sensitivity (OGIS)], insulin secretion (HOMA%B, HOMA2-%B), lipid profile and blood pressure were measured at baseline and at 6 weeks' follow-up.

RESULTS: Seventy-one of the recruited subjects completed the study (35 in supplemented group, 36 in control group). There was an increase in OGIS with supplementation by per protocol analysis (P = 0.038; intention-to-treat analysis P = 0.055). The age- and baseline 25-hydroxyvitamin D level-adjusted difference in change in OGIS was highly significant (mean difference 41.1 +/- 15.5; P = 0.01). No changes in secondary outcome measures (insulin secretion, basal indices of insulin sensitivity, blood pressure or lipid profile) were found with supplementation.

CONCLUSION: The trial indicates that vitamin D(3) supplementation improves postprandial insulin sensitivity (OGIS) in apparently healthy men likely to have insulin resistance (centrally obese but non-diabetic).