The effect of quercetin on stress The Effect of Quercetin on Stress Oxidative Markers: A Systematic Review and Meta-Analysis of Randomized Controlled Clinical Trialsers; A systematic review and meta-analysis of randomized controlled clinical trials

Background: Quercetin is one of the main flavonoids, overall distributed in plants. The antioxidant capacity of quercetin is several times vitamin E and glutathione. This systematic review and meta‐analysis of randomized controlled trials were performed to determine the effect of quercetin on oxidative stress (OS) markers. Methods: A literature search was conducted in PubMed, ISI Web of Science, Scopus, and Google Scholar to February of 2021. Meta-analysis was conducted on 8 eligible RCTs containing a total of 668 participants. The weighted mean difference (WMD) with 95% confidence intervals (CIs) was calculated for a pool effect size of Malondialdehyde (MDA), Total Antioxidant Capacity (TAC), and Ferric Reducing Ability of Plasma (FRAP). Subgroup analyses were performed based on intervention duration and dosage. The heterogeneity of studies was examined by Cochran's Q test and I-squared (I2) statistic. Results: Effect sizes from 668 participants based on the random effect model showed that quercetin supplementation had no significant effect on TAC and MDA compared to the control group. The analysis illustrated that quercetin supplementation significantly increased FRAP in adults (WMD = -0.159 mmol/l, 95% confidence interval (CI):-0.178, -0.141, P ≤ 0.001). Conclusions: The finding of the current study showed that quercetin supplementation had no significant effect on TAC levels, although it significantly increased FRAP levels in adults. Also, MDA level did not markedly change. It has needed to conduct clinical trials with more quality and bigger sample sizes to verify the positive impact of quercetin on stress oxidative marker.