Effects of vitamin D on blood pressure in patients with type 2 diabetes mellitus

Purpose: Previous studies have suggested that vitamin D supplementation may decrease blood pressure in patients with type 2 diabetes, although conflicting results have been reported. The purpose of this meta-analysis was to evaluate the effects of the vitamin D supplementation on blood pressure in patients with type 2 diabetes. Methods: A meta-analysis of published randomized controlled trials was conducted. Eligible studies were identified via a literature search of the MEDLINE (PubMed), EMBASE, and Cochrane Library databases through to May 25, 2015. The endpoint of the analysis was the change in blood pressure due to vitamin D treatment in patients with type 2 diabetes. These changes were calculated as the difference between the baseline and final measurements performed in each study. A fixed-effects model was used to calculate the combined effect estimates; in the presence of heterogeneity, a random-effects model was used. Results: A total of 15 articles were included in the meta-analysis. All 15 articles, including 1,134 patients with type 2 diabetes, were analyzed for systolic blood pressure (SBP), and 13 articles, including 793 patients, were analyzed for diastolic blood pressure (DBP). The combined-effect estimate of vitamin D intervention on SBP was -0.121 mmHg (95% confidence interval (CI) -0.355 to 0.113, p = 0.311), and considerable heterogeneity was observed between studies (p < 0.001, I-2 = 74.2%). For DBP, the combined effect estimate was -0.160 mmHg (95% CI -0.298 to -0.022, p = 0.023), and no heterogeneity was observed (p = 0.673, I-2 = 0.0%). Conclusions: This study is the first meta-analysis of the effect of vitamin D supplementation on blood pressure in patients with type 2 diabetes. This meta-analysis demonstrated that vitamin D supplementation may result in a reduction in DBP in patients with type 2 diabetes. However, additional studies with large sample sizes and longer durations are needed to establish a relationship between vitamin D and blood pressure in patients with type 2 diabetes.