Effect of Green Tea Supplementation on Antioxidant Status in Adults: A Systematic Review and Meta-Analysis of Randomized Clinical Trials
What this study found
Green tea or green tea extract increased total antioxidant capacity (TAC) by 0.20 mmol/L (95% CI 0.09–0.30; p<0.001) across 17 arms. Subgroup effects: TAC higher with >400 mg/day (0.29 mmol/L); shorter interventions (<8 weeks) showed larger gains (0.43 mmol/L) than longer ones (>8 weeks, 0.08); effects observed in both healthy and unhealthy populations; brewing form and extract also increased TAC. MDA decreased non-significantly (−0.00 μmol/L; 95% CI −0.00 to 0.00; p=0.636); meta-regression suggested dose-related changes in MDA but no clear linear dose–duration relationship for TAC. Overall,…
- Study & population
- Adults (>18 years) in randomized controlled trials with parallel-group design; mixed health status (healthy individuals and those with obesity, diabetes, hypercholesterolemia, or β-thalassemia major); 16 RCTs, 17 arms, about 760 participants; sexes varied (some studies included only men or only women, others included both).
- Intervention
- Green tea or green tea extract; oral consumption; duration varied across studies (2–36 weeks); dosage varied (mg/day) across trials.
- Key limitation
- High heterogeneity across studies due to differences in populations, doses, durations, and outcomes; small to moderate sample sizes per trial (8–48); mix of healthy and diseased populations; some risk of bias in blinding; language limited to English; not all oxidative stress markers consistently reported.
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Open PDFOriginal abstract
It is well-established that green tea supplementation has antioxidant properties. However, whether green tea supplementation leads to oxidative stress reduction remains unclear, as clinical investigations on this subject have yielded inconsistent outcomes. Consequently, we aimed to determine the effects of green tea supplementation on oxidative stress in adults. A systematic search of English language publications up to 21 August 2021 was carried out in PubMed, Scopus, Embase, and ISI Web of Science, utilizing pertinent keywords. These searches included randomized controlled trials (RCTs) evaluating the relationship between green tea supplementation, malondialdehyde (MDA), and total antioxidant capacity (TAC) in adults. A random-effects model was used to estimate the weighted mean difference (WMD) and 95% confidence intervals (95% CI). Meta-regression and non-linear dose-response analyses were performed to investigate the association between the dosage of green tea (mg/day) and the duration of the intervention (weeks) with pooled effect size. Sixteen RCTs with seventeen arms including 760 participants met the inclusion criteria. Our results indicated that green tea supplementation had significant effects on TAC (weighted mean difference [WMD]: 0.20 mmol/L; 95% CI: 0.09, 0.30, p < 0.001) and significant heterogeneity between studies (I2 = 98.6%, p < 0.001), which was largely related to gender and body mass index (BMI). Subgroup analysis in TAC identified a significant relationship except with low dose supplementation and obese individuals. No relationship between MDA and green tea supplementation was observed in any subgroups; however, meta-regression analysis revealed a linear inverse association between the dosage and significant change in MDA (r = −2117.18, p = 0.017). Our outcomes suggest that green tea supplementation improves TAC and affects MDA based on the dose of the intervention in adults. Future RCTs with longer durations are needed to expand our findings.