Effect of antioxidant vitamin supplementation on endothelial function in type 2 diabetes mellitus: a systematic review and meta‐analysis of randomized controlled trials

Summary Controversy exists among trials assessing whether prolonged antioxidant vitamin supplementation improves endothelial function in type 2 diabetes mellitus ( T2DM ) subjects. The aim of this study was to systematically review and quantify the effect of antioxidant vitamin supplementation on endothelial function in T2DM subjects. MEDLINE , C ochrane, S copus and W eb of S cience were searched up to F ebruary 2013 for randomized controlled trials assessing the effect of antioxidant vitamin E and/or C supplementation on endothelial function in T2DM subjects. Ten randomized controlled trials comparing antioxidant vitamin‐supplemented and control groups (overall n  = 296) met the inclusion criteria. Post‐intervention standardized mean difference ( SMD ) in endothelial function did not reach statistical significance between groups (0.35; 95% confidence interval = −0.17, 0.88; P  = 0.18). In subgroup analysis, post‐intervention endothelial function was significantly improved by antioxidant vitamin supplementation in T2DM subgroups with body mass index ( BMI ) ≤ 29.45 kg m −2 ( SMD  = 1.02; P  < 0.05), but not in T2DM subgroups with BMI  > 29.45 kg m −2 ( SMD  = −0.07; P  = 0.70). In meta‐regression, an inverse association was found between BMI and post‐intervention SMD in endothelial function ( B  = −0.024, P  = 0.02). Prolonged antioxidant vitamin E and/or C supplementation could be effective to improve endothelial function in non‐obese T2DM subjects.