Vitamin E Supplementation and Circulating Adiponectin Concentrations: A Systematic Review and Meta-Analysis of Randomized Controlled Trials

Current results from clinical trials about vitamin E effects on adiponectin are ambiguous. Therefore, we conducted a meta-analysis of available RCTs to resolve this inconsistency. The systematic search was performed in several databases including SCOPUS, PubMed-Medline, and Google Scholar until October 1st, 2017. We used fixedeffects model in combination with mean difference (MD) and 95% confidence intervals (CI) for the analysis of data. Meta-analysis of 6 RCTs (9 treatment arms) showed a significant increase in circulating adiponectin levels (MD: 0.36 ug/ml, 95% CI: 0.16 to 0.56; p<0.001), following vitamin E supplementation. In sub-group analysis, a significant increasing effect was observed only in trials with ≥400 mg/day dosage (MD: 0.78 ug/ml, 95% CI: 0.31, 1.24, p=0.001) and those trials lasting ≥6 months (MD: 0.58 ug/mL, 95% CI: 0.29, 0.86, p<0.001). In meta-regression, there was association between changes in adiponectin concentrations and duration of supplementation. Our findings showed the significant increase effect of vitamin E supplementation on circulating adiponectin levels, however a significant increasing effect was observed at doses above 400 mg/day and when supplementation lasting over 6 months.