Effects of supplementation with green tea catechins on plasma C-reactive protein concentrations: A systematic review and meta-analysis of randomized controlled trials.

BACKGROUND Promising experimental and clinical trials suggest that green tea decreases the inflammatory process in cardiometabolic diseases, but evidence from epidemiologic studies about the effects on plasma C-reactive protein (CRP) seems inconsistent and ambiguous. Therefore, the aim of this meta-analysis was to evaluate the effects of green tea supplementation on plasma CRP concentrations. METHODS We searched selected database up to October 26, 2014 to identify randomized controlled trials (RCTs) investigating the effects of green tea supplementation on plasma CRP concentrations. Two independent reviewers extracted data on study characteristics, methods, and outcomes. RESULTS Meta-analysis of data from 11 RCTs arms did not indicate a significant effect of supplementation with green tea catechins on plasma CRP concentrations (weighted mean difference [WMD], 0.085 mg/L; 95% confidence interval [CI], -0.225 to 0.395; P = 0.592). This effect size was robust in sensitivity analysis and omission of each individual study did not have a significant effect. The nonsignificant effects of green tea catechins on plasma CRP concentrations were also observed in subgroups of studies with green tea supplementation with a duration of <8 wk (WMD, 0.029 mg/L; 95% CI, -0.229 to 0.286; P = 0.828) and ≥8 wk (WMD, 0.099 mg/L; 95% CI, -0.555 to 0.754; P = 0.766). Likewise, there was no significant effect in subgroups of studies with total catechins doses <400 mg/d (WMD, 0.073 mg/L; 95% CI, -0.251 to 0.398; P = 0.658) and ≥400 mg/d (WMD, 0.213 mg/L; 95% CI, -0.148 to 0.574; P = 0.247). The effect sizes were not significant after stratification of studies to those recruiting healthy subjects (WMD, -0.028 mg/L; 95% CI, -0.216 to 0.160; P = 0.769), and those recruiting participants with cardiometabolic diseases (WMD, 0.260 mg/L; 95% CI, -0.815 to 1.334; P = 0.636). CONCLUSIONS This meta-analysis of data from 11 RCT arms did not indicate a significant effect of supplementation with green tea catechins on plasma CRP concentrations. Furthermore, well-designed trials are necessary to validate these results.