Effect of vitamin D supplementation on oral glucose tolerance in individuals with low vitamin D status and increased risk for developing type 2 diabetes (EVIDENCE): A double-blind, randomized, placebo-controlled clinical trial

Aims: Low serum 25-hydroxyvitamin-D (25(OH)D) concentrations are associated with insulin resistance, beta-cell dysfunction and type 2 diabetes. We conducted a 24-week double-blind, randomized, placebo-controlled trial to examine the effect of 28 000 IU of vitamin D-3 once weekly on plasma glucose after a 2 hour-75 g oral glucose tolerance test (2hrPC glucose), insulin sensitivity and beta-cell function. Study Design and Methods: A total of 71 participants with serum 25(OH) D <= 65 nmol/L, impaired fasting glucose and elevated glycated hemoglobin were randomly assigned to receive 28 000 IU of vitamin D-3 (VitD; n = 35) or placebo (n = 36) in cheese once weekly for 24 weeks. The primary outcome was the change in 2hPC glucose. Secondary outcomes were fasting glucose, fasting and postprandial insulin, indices of insulin sensitivity and beta-cell function, glycated hemoglobin and lipid profile. Participants underwent an oral glucose tolerance test to determine 2hPC glucose. Results: Mean baseline serum 25(OH) D was 48.1 and 47.6 nmol/L in the VitD and placebo groups, respectively. Serum 25(OH) D significantly increased to 98.7 nmol/L (51 nmol/L increase; P <.0001) in the VitD group. No significant differences in fasting (P =.42) or 2hPC glucose (P =.55) or other indices of glucose metabolism, including beta-cell function and insulin sensitivity, were observed between groups. A subgroup analysis of individuals with 25(OH) D < 50 nmol/L and prediabetes did not change these results. The VitD group exhibited a significant reduction in LDL cholesterol (-0.27 vs 0.01 mmol/L, P =.03). Conclusion: Weekly doses of vitamin D-3 in individuals with suboptimal vitamin D levels who were at risk for type 2 diabetes did not improve oral glucose tolerance or markers of glycaemic status.