Int J Cancer. 2019 Dec 13. doi: 10.1002/ijc.32824. [Epub ahead of print]
Laboratory studies have observed chemopreventive effects of black and green tea on breast cancer development, but few epidemiologic studies have identified such effects. We investigated the association between tea consumption and breast cancer risk using data from 45,744 U.S. and Puerto Rican women participating in the Sister Study. Frequency and serving size of black and green tea consumption were measured at cohort enrollment. Breast cancer diagnoses were reported during follow-up and confirmed by medical record review. Multivariable Cox proportional hazards regression was used to estimate hazard ratios (HR) and 95% confidence intervals (CI). We further investigated potential variation according to estrogen receptor (ER) status, menopausal status, and body mass index (BMI). Overall, 81.6% and 56.0% of women drank black or green tea, respectively. A total of 2,809 breast cancer cases were identified in the cohort. The multivariable model suggested an inverse association between black (≥5 vs. 0 cups/week: HR=0.88, 95% CI 0.78, 1.00, p-trend=0.08) and green tea (≥5 vs. 0 cups/week: HR=0.82, 95% CI 0.70, 0.95, p-trend<0.01) consumption and breast cancer risk. We did not observe differences by ER characteristics, menopausal status, or BMI. In conclusion, our study suggests drinking at least 5 cups of green or black tea per week may be associated with decreased breast cancer risk.