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

Aim To determine the short‐term effect of vitamin D3 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 ≥ 35 years received three doses of vitamin D3 (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 D3 supplementation improves postprandial insulin sensitivity (OGIS) in apparently healthy men likely to have insulin resistance (centrally obese but non‐diabetic).