Influence of vitamin D supplementation on glycemic control in type 2 diabetics.

Several studies have suggested a benefic impact of vitamin D supplementation on glycemic control and insulin resistance among patients with type 2 diabetes mellitus. The aims of our study were to assess vitamin D status in individuals with type 2 diabetes mellitus and to investigate the effects of vitamin D supplementation on glycemic measures in patients having vitamin D deficiency. We conducted a comparative prospective study involved 100 Tunisian patients with type 2 diabetes followed at the National Institute of Nutrition and Food Technology of Tunis. Glycemic control and insulin resistance were evaluated in the beginning of the study and three months after supplementation. Baseline mean 25-Hydroxy vitamin D  (25(OH)D) level was 17.5±9.8 ng/ml. Vitamin D status was deficient in 60%, insufficient in 26% and sufficient in 14% patients. After vitamin D supplementation, mean serum 25(OH)D concentration increased significantly (p˂10-3). We observed a negative correlation between the variation of plasma 25(OH)D level and the waist circumference's variation (r=-0.266 and p=0.018). This correlation persisted after adjustment for therapeutic management. Vitamin D supplementation did significantly improve neither glycemic control nor insulin resistance parameters. Vitamin D deficiency is frequent in patients with type 2 diabetes mellitus. The metabolic effects of supplementation are controversial, hence the need of expanding studies to better demonstrate these effects.