Impaired glucose tolerance in vitamin d deficiency can be corrected by calcium

Vitamin D3, via its active metabolite 1α,25-dihydroxyvitamin D3, helps maintain normal calcium levels in the body. Apart from the maintenance of calcium homeostasis, the active form of vitamin D3 is now known to be involved in a number of other functions including that of pancreatic β cells. Low serum insulin levels and impaired glucose tolerance in a vitamin D-deficient state have been reported in experimental animals. Hypocalcemia is a major consequence of vitamin D deficiency. Whether the impairment observed is due to vitamin D deficiency per se or is secondary to low calcium is still a matter of controversy. The present study was conducted to delineate the roles of vitamin D and calcium in glucose intolerance associated with vitamin D deficiency in vivo. It was found that supplementation with either vitamin D3 or high calcium alone to vitamin D-deficient rats could correct the defects. In addition, insulin sensitivity was found to be enhanced in the vitamin D-deficient group compared with vitamin D control or calcium-supplemented groups. Hence the present study demonstrates that calcium per se in the absence of vitamin D increases insulin secretion and normalizes intolerance to glucose seen in vitamin D deficiency.