Assessment of Vitamin D Supplementation Effect on Insulin Resistance among Type 2 Diabetic Patients

The etiological role of vitamin D deficiency in glucose tolerance and type 2 diabetes is well defined. it can reduce insulin secretion and, therefore, impair glucose tolerance. The present study was designed to determine the effects of vitamin D supplementation on insulin resistance in type 2 diabetic patients. This study was a double-bind clinical trial. Fifty-seven diabetic patients (34 males and 23 females) being treated with oral hypoglycemic agents who had normal serum calcium level, were enrolled in the study. The study was conducted in winter (when the vitamin D is in its lowest level in Iran). The patients were randomly divided into 2 groups and received 1500 IU/d oral vitamin D3 or placebo for 1 month. Fasting glucose, insulin, C- peptide, serum 25-hydroxy-vitamin D and Quantitative Insulin Sensitivity Check Index (QUICKI) were evaluated before and after the treatment. Measurement of energy, macronutrients, fiber, vitamin E, vitamin C, Magnesium, Zinc, Calcium and vitamin D status intake was performed in the onset, during and at the end of the study. The mean of primary serum level of 25-hydroxy-vitamin D was 10.42±10.67 ng/ml. 47 subjects (82.5%) out of 57 ones were vitamin D deficient. After the treatment, only 60% of patients in vitamin D-received group achieved normal level of 25-hydroxy-vitamin D. Fasting glucose and insulin decreased in vitamin D-received group, although it was not significant. Serum C-peptide level increased significantly in vitamin D-received group from 2.47±0.88 ng/ml (in pre-treatment stage) to 2.78±1.14 ng/ml (in post-treatment stage) (P<0.02). Serum Calcium level increased significantly in vitamin D-received group (P<0.04), however, it remained at a normal range. The mean of changes of QUICKI was significantly higher in vitamin D-received group than that of placebo group in post-treatment stage (P<0.03). It indicates that insulin resistance was reduced in this group. Results of this study suggest that vitamin D supplementation can reduce insulin resistance in type 2 diabetic patients and it should be, therefore, recomended to improve the control of diabetes, especially in winter.