Effects of Green Tea Supplementation on Chemoprevention at Different Stages of Carcinogenesis: A Systematic Review.

Green tea catechins have chemopreventive potential; however, the clinical evidence remains inconsistent. This review evaluated the effects of supplementation with green tea derivatives on chemoprevention at different stages of carcinogenesis. PubMed, Embase, Web of Science, Scopus, the Cochrane Library, CINAHL, and Google Scholar were searched for randomised and non-randomised clinical trials in adults. Random-effects meta-analyses were used to estimate relative risks (RRs) and 95% confidence intervals (95% CIs). Risk of bias and certainty of the evidence were assessed using RoB 2, ROBINS-I, and GRADE. Of the 7089 records identified, 19 studies, comprising a total of 3121 participants, were included. Nine studies were included in the meta-analyses. No statistically significant associations were observed for regression of cervical lesions (RR = 2.40; 95% CI: 0.36-16.23), HPV clearance (RR = 1.19; 95% CI: 0.68-2.07), prostate cancer incidence (RR = 0.52; 95% CI: 0.22-1.23), or colorectal adenoma recurrence (RR = 0.71; 95% CI: 0.50-1.00). The qualitative synthesis showed heterogeneous findings, including favourable effects on some biomarkers. The certainty of the evidence was rated as low or very low. Although no association was observed between green tea supplementation and the outcomes evaluated in the meta-analyses, the findings should be interpreted with caution because of methodological heterogeneity, risk of bias, and the low or very low certainty of the evidence. Clinical trials with larger sample sizes and populations that are more comparable in terms of the type and stage of carcinogenesis are needed to clarify the chemopreventive potential of green tea supplementation.