Does high-dose vitamin D supplementation impact insulin resistance and risk of development of diabetes in patients with pre-diabetes? A double-blind randomized clinical trial

The aim of this study is to evaluate the effect of high-dose vitamin D on insulin sensitivity and the risk of progression to diabetes.In this double-blind, placebo-controlled randomized clinical trial adults with pre-diabetes and vitamin D deficiency were randomly assigned to either vitamin D3 or placebo. Fasting plasma glucose (FPG), 2-h oral glucose tolerance test plasma glucose (OGTT PG), Homeostatic Model Assessment of Insulin Resistance (HOMA-IR), and the rate of progression of glucose tolerance was compared.A total of 162 patients were randomized, from which 83 finished the 6-month follow-up (44 in intervention group and 39 in control group). In 6 months, serum 25-hydroxyvitamin D levels were significantly higher in the intervention group (36 ng/ml vs 16 ng/ml, P value < 0.001). There was no significant difference between FPG or 2H-OGTT PG in two groups. HOMA-IR score was significantly lower in the vitamin D group (2.6 vs. 3.1; P value = 0.04). The rate of progression toward diabetes was significantly lower in the intervention group (28% vs. 3%; P value = 0.002).In patients with pre-diabetes and hypovitaminosis D, high dose vitamin D improves insulin sensitivity and decreases risk of progression toward diabetes.