THE EFFECT OF VITAMIN D3 ON INSULIN SECRETION AND PERIPHERAL INSULIN SENSITIVITY IN TYPE 2 DIABETIC PATIENTS

Abstract

SUMMARY: The aim of this study was to evaluate the effect of vitamin D 3 supplementation on insulin secretion and insulin resistance. Ten females with type 2 diabetes being treated with oral hypoglycaemic agents and with normal serum and urine calcium levels were enrolled in the study. The study was conducted in March, when levels of vitamin D are lowest in our region. The level of plasma 25(OH)D was measured (normal range in winter 25–120 nmol/l). The first (FPIS) and second (SPIS) phases of insulin secretion were studied during IVGTT Peripheral insulin resistance was measured. A group of 17 age‐ and BMI‐matched females with normal glucose tolerance served as a control group. The diabetic patients were treated with cholecalciferol 1332 IU daily for one month. The mean plasma 25(OH)D level was 35.3±15.1 nmol/l at baseline, 70% of patients being vitamin D deficient. After one month of treatment with vitamin D 3, the plasma 25(OH)D level increased by a mean of 75.8%; 70% of the patients achieved normal vitamin D levels. FPIS increased significantly by 34.3%, while the change in SPIS of 20.4% was not significant (p>0.8). We found a significant correlation between the change in FPIS and the change in 25(OH)D level after vitamin D 3 supplementation (p<0.018). The results showed a decrease of 21.4% in insulin resistance after one month, but the change was not significant. Bearing in mind that the main defects in type 2 diabetes mellitus are reduced FPIS and insulin resistance, and the favourable effect vitamin D 3 had on them, we suggest vitamin D 3 deficiency may at least partly contribute to the impairment of insulin secretion and probably of insulin action. Our results suggest that vitamin D 3 supplementation could be an element in the complex treatment of type 2 diabetes mellitus during the winter.