Normal 25(OH)D levels are important for fully normal calcium absorption efficiency in the gut. Calcium absorption in the gut plateaus at 25(OH)D levels of 30 ng/ml. Vitamin D influences pancreatic β-cell synthesis, secretion and insulin sensitivity. Vitamin D may mediate the levels of extracellular and intracellular calcium [(Ca2+)i] through a rapid response involving flux through β cells. Vitamin D deficiency affects insulin secretion and sensitivity by its effects on (Ca2+)i. It plays a key role in ensuring preservation of extracellular calcium levels and intracellular cytosolic calcium concentration. Vitamin D supplementation - Correction of deficiency: 10,000 IU daily or 60,000 IU weekly for 8-12 weeks; 6,00,000 by IM injections once with a gap of 2 months. Vitamin D maintenance dose:1,000-2,000 IU daily or 10,000 IU weekly or 60,000 IU once a month. This should be accompanied by calcium intake of 1 g/day in adults. Casual exposure to the mid-day sun for 15-30 minutes exposing 12% of body surface area without sunscreen will synthesize enough vitamin D for the day. Exposure of larger skin surface area is required in the elderly.