Green tea consumption and risk of breast cancer: A systematic review and updated meta-analysis of case-control studies

Background: As the most popular beverage in East Asia, green tea (GT) has various biological activities effects such as antimutation, anti-oxidation, and anti-tumor. In this study, we aimed to evaluate whether GT consumption could be an effective way to decrease the risk of breast cancer. Methods: We had performed a systematic review and updated meta-analysis of published case-control studies to evaluate the association between GT intake and the risk of breast cancer. Searching strategies were performed by the following keywords "Breast cancer, " "breast neoplasm, " and "green tea, " with derivations and different combinations. The following databases were searched: PubMed, Cochrane Library, EMBASE, Web of science, China National Knowledge Infrastructure, WanFang, and China Biology Medicine disc. Studies published in both English and Chinese were considered for inclusion. Risk of bias was assessed through the Newcastle-Ottawa Scale (NOS). All data were analyzed through using Review Manager 5.1 software. Results: Fourteen studies fulfilled inclusion criteria for meta-analysis, yielding a total of 14, 058 breast cancer patients and 15, 043 control subjects. Individuals with the habit of drinking GT were found to have a negative association with the risk of future breast cancer (odds ratio 0.83; 95% confidence interval: 0.72-0.96) despite significant heterogeneity. In subgroup analyses, the negative correlation was still found in studies using registry-based controls, NOS grades ≥6 and the number of cases <500. Conclusions: GT consumption may have a decreased incidence of breast cancer despite significant heterogeneity. However, owing to the quality of available studies, more properly designed trials are warranted to clarify the association between GT consumption and breast cancer. Abbreviations: CBM= China Biology Medicine disc, CIs = confidence intervals, CNKI = China National Knowledge Infrastructure, GT = green tea, NOS = Newcastle-Ottawa Scale, ORs = odds ratios, PRISMA = Preferred Reporting Items for Systematic Reviews and Meta-analysis, RRs = risk ratios.