Effect of green tea supplementation on blood pressure among overweight and obese adults: a systematic review and meta-analysis

Background: Emerging randomized controlled trials (RCTs) investigating the effect of green tea or green tea extract (GTE) supplementation on blood pressure (BP) among overweight and obese adults reported inconsistent findings. Objective: To conduct a systematic review and meta-analysis to clarify the efficacy of green tea or GTE on BP among overweight and obese adults. Methods: Electronic databases, conference proceedings and gray literature were searched systematically to include parallel and cross-over RCTs examining the efficacy of green tea or GTE on BP compared with placebo. Data were meta-analyzed using a random-effects model, to compare the mean difference of the change in BP from baseline in the intervention and the placebo groups. Results: Fourteen RCTs with 971 participants (47% women) were pooled for analysis. Green tea or GTE produced a significant effect on both SBP (mean difference -1.42 mmHg, 95% confidence interval -2.47 to -0.36, P = 0.008; I-2 = 52%, P = 0.01 for heterogeneity) and DBP (mean difference -1.25 mmHg, 95% confidence interval -2.32 to -0.19, P = 0.02; I-2 = 74%, P < 0.001 for heterogeneity), compared with placebo. The quality of evidence across studies was low. Similar results were found in subgroup and sensitivity analyses. Conclusion: Among overweight and obese adults, green tea or GTE supplementation is found to cause a small but significant reduction in BP. More high-quality RCTs with large sample sizes are needed to further confirm the efficacy on BP and make strong recommendations for green tea or GTE supplementation among the overweight and obese adults.