A double-blind, randomized, placebo-controlled trial of the short-term effect of vitamin D3 supplementation on insulin sensitivity in apparently healthy, middle-aged, centrally obese men

To determine the short-term effect of vitamin D-3 supplementation on insulin sensitivity in apparently healthy, middle-aged, centrally obese men. A double-blind randomized controlled trial was conducted at a tertiary care facility in which 100 male volunteers aged >= 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. 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. 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). Diabet. Med. 26, 19-27 (2009).