Vitamin D supplementation enhanced oral glucose tolerance in normoglycemic rats and insulin sensitivity in rats fed high fat emulsion

Several reports have suggested possible role of vitamin D deficiency in the pathogenesis of both type 1 and 2 diabetes. However, there is no agreement on the level of vitamin D requirement for optimum glycemic control. This work evaluated the effect of vitamin D supplementation on oral glucose tolerance (OGT) and insulin sensitivity, with the aim of determining the possible supplementation rate of vitamin D required for optimum glycemic control. Oral glucose tolerance was evaluated in normoglycemic rats, with vitamin D supplementation (VDS) at the rate of 0.07, 0.14, and 0.35 μg/kg orally for 28 days. Oral glucose tolerance (OGT) was evaluated by administration of 2000 mg/kg glucose/rat orally and blood glucose determined at 30, 60, and 120 min post glucose administration. Insulin sensitivity was evaluated in normoglycemic rats fed high fat emulsion (HFE) at the rate of 5 ml/kg/rat for 10 days and VDS was at the rate of 0.04, 0.05, 0.07, and 0.35 μg/kg for 38 days. Insulin (0.05 u/kg) was injected intraperitoneally to each rat, and blood glucose level determined at 5, 30, 60, and 120 min post insulin administration. Blood glucose of VDS rats was significantly (p < 0.05) lower than the vitamin D restricted group at 120 min. Significantly, (p < 0.05) higher OGT was recorded in the VDS groups. Insulin sensitivity (K) values showed inverse dose dependency with higher K values at lower vitamin D doses. Vitamin D supplementation enhanced glucose tolerance and insulin sensitivity at lower doses.