In this systematic review and meta-analysis of randomized controlled trials (RCTs), the effects of vitamin D supplementation on biomarkers of inflammation and oxidative stress in diabetic patients are summarized. The following databases were searched up to December 2017: MEDLINE, EMBASE, Web of Science, and Cochrane Central Register of Controlled Trials. The quality of the relevant extracted data was assessed according to the Cochrane risk of bias tool. Data were pooled using the inverse variance method and expressed as mean difference with 95% Confidence Intervals (95% CI). Heterogeneity between studies was assessed by the Cochran Q statistic and I-squared tests (I2). Overall, 33 studies were included in the meta-analyses. Vitamin D supplementation were found to significantly reduce serum high-sensitivity C-reactive protein (hs-CRP) (WMD 0.27; 95% CI, - 0.35, - 0.20; p<0.001) and malondialdehyde (MDA) levels (WMD - 0.43, 95% CI - 0.62, - 0.25, p<0.001) in diabetic patients. In addition, vitamin D supplementation were found to increase markers of nitric oxide (NO) release (WMD 4.33, 95% CI 0.96, 7.70), total serum antioxidant capacity (TAC) (WMD 57.34, 95% CI 33.48, 81.20, p<0.001) and total glutathione (GSH) levels (WMD 82.59, 95% CI 44.37, 120.81, p<0.001). Overall, this meta-analysis shows that in diabetic patients, taking vitamin D had significant effects on hs-CRP and MDA levels, and significantly increased NO, TAC and GSH levels.
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