Abstract

Abstract Aims To test whether a single large dose of vitamin D2 can improve endothelial function in patients with Type 2 diabetes mellitus and low serum 25‐hydroxyvitamin D levels. Methods Double‐blind, parallel group, placebo‐controlled randomized trial. A single dose of 100 000 IU vitamin D2 or placebo was administered to patients with Type 2 diabetes over the winter, when levels of circulating 25‐hydroxyvitamin D were likely to be lowest. Patients were enrolled if their baseline 25‐hydroxyvitamin D level was < 50 nmol/l. Endothelial function and blood pressure were measured and fasting blood samples were taken at baseline and 8 weeks after administration of vitamin D. Results Forty‐nine per cent of subjects screened had 25‐hydroxyvitamin D levels < 50 nmol/l. Thirty‐four subjects completed the study, with a mean age of 64 years and a baseline 25‐hydroxyvitamin D level of 38.3 nmol/l. Vitamin D supplementation increased 25‐hydroxyvitamin D levels by 15.3 nmol/l relative to placebo and significantly improved flow mediated vasodilatation (FMD) of the brachial artery by 2.3%. The improvement in FMD remained significant after adjusting for changes in blood pressure. Vitamin D supplementation significantly decreased systolic blood pressure by 14 mmHg compared with placebo; this did not correlate with change in FMD. Conclusions Vitamin D insufficiency is common in patients with Type 2 diabetes during winter in Scotland. A single large dose of oral vitamin D2 improves endothelial function in patients with Type 2 diabetes and vitamin D insufficiency.