BACKGROUND Vitamin D has recently been given a lot of attention for its role in controlling insulin secretion. Many studies have spoken of its role in weight management, blood sugar control and many other metabolic variables. PATIENT AND METHODS In a randomized double-blind clinical trial, 210 people with vitamin D deficiency were randomly allocated into two groups receiving vitamin D (50,000 units per week) or placebo for 8 weeks. RESULTS Vitamin D levels were significantly increased in the group receiving vitamin D supplementation (13.7±5.2 unit increase versus 0.8±2.8). The increased levels of vitamin D lead to significant changes in fasting insulin levels (6.8±8.1 unit reduction versus 2.3±3.7), a 2-h insulin (31.1±34.9 unit reduction versus 4.5±24.6) and Homeostasis Model Assessment (HOMA) indices. CONCLUSION Correction of vitamin D deficiency leads to increased insulin sensitivity that was significantly able to maintain glucose in the normal range with lower levels of insulin.