The effects of garlic supplementation on oxidative stress markers: A systematic review and meta-analysis of randomized controlled trials

•Data obtained from 7 studies with 317 participants were meta-analyzed.•It seems that garlic supplementation significantly decreases the serum levels of malondialdehyde.•It seems that garlic supplementation significantly increases the total antioxidant capacity. Recent studies have found that garlic supplementation can improve antioxidant status, however, there is no definitive consensus on this context. The present systematic review and meta-analysis aimed to investigate the effect of garlic supplementation on oxidative stress markers. We searched titles, abstracts, and keywords of relevant articles indexed in PubMed, ISI Web of Science, Scopus, and Google Scholar databases up to November 2019 to identify eligible RCT studies. To compare the effects of garlic with placebo, weighted mean difference (WMD) with 95 % confidence intervals (CI) were pooled based on the random-effects model. Quality assessment was performed using a Cochrane risk of bias assessment tool. Overall, 7 randomized controlled trials (RCTs) with 317 participants were included in this meta-analysis. Based on the Cochrane Collaboration Risk of Bias tool, five studies were considered as good quality and two studies were fair. We found that garlic supplementation significantly increased total antioxidant capacity (TAC) (WMD =11.03 mmol/L; 95 % CI: 4.78, 17.28 mmol/L; P < 0.001) and decreased malondialdehyde (MDA) levels (WMD = −1.88 mmol/L; 95 % CI: −3.30, −0.46 mmol/L; P = 0.01) compared with the control group. In summary, the current meta-analysis indicated that garlic supplementation might improve oxidative stress markers. However, these findings are incomplete due to the paucity of studies, and further well-designed clinical trials are needed in this field to confirm the effect of garlic supplement on oxidative stress markers.