There is substantial in vitro and in vivo evidence implicating
tea polyphenols as chemopreventive agents against various
cancers. However, epidemiologic data obtained from mainly Western populations are not supportive of a protective role of
tea, mainly
black tea, in the etiology of
breast cancer. Much less is known about the relationship between
green tea and
breast cancer risk. During 1995-1998, we conducted a population-based, case-control study of
breast cancer among Chinese, Japanese and Filipino women in Los Angeles County and successfully interviewed 501
breast cancer patients and 594 control subjects. Detailed information on menstrual and reproductive factors; dietary habits, including intake of black and
green tea; and other lifestyle factors was collected. Risk of
breast cancer was not related to
black tea consumption. In contrast,
green tea drinkers showed a significantly reduced risk of
breast cancer, and this was maintained after adjusting for age, specific Asian ethnicity, birthplace, age at menarche, parity, menopausal status, use of menopausal
hormones, body size and intake of total calories and
black tea. Compared to women who did not drink
green tea regularly (i.e., less than once a month), there was a significant trend of decreasing risk with increasing amount of
green tea intake, adjusted odds ratios being 1.00, 0.71 (95% confidence interval [CI] 0.51-0.99) and 0.53 (95% CI 0.35-0.78), respectively, in association with no, 0-85.7 and >85.7 ml of
green tea per day. The significant inverse association between risk of
breast cancer and
green tea intake remained after further adjustment for other potential confounders, including smoking; alcohol,
coffee and
black tea intake; family history of
breast cancer; physical activity; and intake of soy and dark green vegetables. While both
green tea and soy intake had significant, independent protective effects on
breast cancer risk, the benefit of
green tea was primarily observed among subjects who were low soy consumers. Similarly, the protective effect of soy was primarily observed among subjects who were nondrinkers of
green tea. In summary, our results point to an important role of both
green tea and soy intake in relation to
breast cancer risk in Asian-American women.