Vitamin D Versus Placebo in Improvement of Endothelial Dysfunction: A Meta‐Analysis of Randomized Clinical Trials

AIMS: The possible effect of vitamin D administration in humans on endothelial dysfunction (ED) still remains undetermined. The current meta-analysis was performed to evaluate if vitamin D could improve ED. METHODS: Randomized, double-blind, and placebo-controlled clinical trials were identified by systematic search of the PubMed, the Cochrane Library, the Web of Science and the Scopus data bases, as well as different reviews and clinical trials articles. A random effects model was used to calculate the pooled overall effect on flow-mediated dilation (FMD) linked to the vitamin D administration. Meta-regression and subgroup analyses were performed to evaluate the impact of study characteristics on the effect of vitamin D administration on FMD. RESULTS: A total of eight studies with nine relevant study arms were identified. The obtained results of pooled analysis showed that vitamin D administration did not improve FMD (eight studies, 529 subjects; weighted mean difference (WMD): 0.96%, 95% CI: -1.24% to 2.06%; P = 0.09). This was probably due to significant heterogeneity in between included trials (I(2) = 84%, P < 0.00001). On the other hand, subgroup analysis demonstrated that vitamin D improved FMD in trials that lasted <16 weeks; if systolic blood pressure (SBP) was higher than 140 mmHg and in trials where diastolic blood pressure (DBP) was <80 mmHg. CONCLUSION: Although the current evidence clearly demonstrates that in certain conditions vitamin D can improve ED, a larger number of clinical trials are needed to confirm this assumption to confirm or reject the final statement on this topic.