Randomized controlled trial of vitamin D supplement on endothelial function in patients with type 2 diabetes

Background: Suboptimal vitamin D status is associated with endothelial dysfunction and an increased risk of cardiovascular diseases but it is unclear whether vitamin D supplementation is beneficial. The aim was to investigate the effect of vitamin D supplementation on endothelial function in patients with type 2 diabetes mellitus (DM). Methods: In a double-blind, placebo-controlled trial, we randomized 100 type 2 DM patients to vitamin D supplement (5000 IU/day, n = 50) or placebo (controls, n 50) for 12 weeks. Assessment of vascular function with brachial artery flow-mediated dilatation (FMD), circulating levels of endothelial progenitor cells (EPCs) and brachial-ankle pulse wave velocity, and metabolic parameter, high-sensitivity C-reactive protein (hsCRP) and oxidative stress markers were performed before and after the supplementation. Results: After 12 weeks, vitamin D treated patients had significant increases in serum 25-hydroxyvitamin D [25(OH) D] concentration (treatment effect 34.7 ng/mL, 95% CI 26.4-42.9, P < 0.001) and serum ionized calcium (treatment effect 0.037 mmol/L, 95% CI 0.007-0.067, P = 0.018); decreased serum parathyroid hormone concentration (treatment effect -0.55 pmol/L, 95% CI -1.08 to -0.02, P = 0.042) compared to patients who received placebo. Nevertheless, vitamin D supplementation did not improve vascular function as determined by FMD, circulating EPC count or baPWV (all P > 0.05). Furthermore, hsCRP, oxidative stress markers, low-and high-density lipoprotein and glycated hemoglobin were also similar between two groups (all P > 0.05). Conclusion: In patients with type 2 DM, 12 weeks oral supplementation of vitamin D did not significantly affect vascular function or serum biomarkers of inflammation and oxidative stress.