The association between green tea consumption and breast cancer risk: A systematic review and meta-analysis

Phytother Res. 2018 Oct;32(10):1855-1864. doi: 10.1002/ptr.6124. Epub 2018 Jun 7. . Najaf Najafi M1, Salehi M1,2, Ghazanfarpour M3, Hoseini ZS4, Khadem-Rezaiyan M5. Author information 1 Clinical Research Unit, Mashhad University of Medical Sciences, Mashhad, Iran. 2 Cancer Research Center, Mashhad University of Medical Sciences, Mashhad, Iran. 3 Evidence-Based Care Research Centre, Department of Midwifery, School of Nursing and Midwifery, Mashhad University of Medical Sciences, Mashhad, Iran. 4 Student Research Committee, Faculty of Medicine, Islamic Azad University of Mashhad, Mashhad, Iran. 5 Faculty of Medicine, Mashhad University of Medical Sciences, Mashhad, Iran. Abstract This systematic review and meta-analysis aimed to critically evaluate the relation between green tea (GT) consumption and the risk of breast cancer. Popular electronic databases were systematically searched for papers in English language. All case-control and cohort studies in addition to randomized clinical trials were included if they assessed the chemopreventive effects of GT on breast cancer. The quality of included studies was assessed using the Newcastle-Ottawa and Jadad scale. This systematic review comprised 14 studies: 9 case-control studies, 4 cohort studies, and 1 clinical trial. Odds ratio (OR) in case-control studies suggested that women in the group receiving the highest level of GT had 19% reduction in breast cancer risk compared with those who received the lowest level of GT (summary OR = 0.81, p = .031; 95% CI [0.66, 0.981]; heterogeneity, I2 = 71.53, p < .001, random effect model; 9 studies). OR in cohort studies also showed no significant difference (OR = 0.99, p = .94; 95% CI [0.81, 1.138]; heterogeneity, I2 = 19.06, p = .29; fixed-effect model; 4 studies). According to the only clinical trial, treatment with GT could not alter the mammographic density compared with placebo (26% vs. 25%). It cannot be concluded that GT consumption may decrease the risk of breast cancer. Due to high heterogeneity, a pooled analysis of case-control and cohort studies was not performed. KEYWORDS: Camellia sinensis; breast cancer; green tea PMID: 29876987 DOI: 10.1002/ptr.6124