Green tea intake is associated with urinary estrogen profiles in Japanese-American women

SCOPE Intake of green tea may reduce the risk of breast cancer; polyphenols in this drink can influence enzymes that metabolize estrogens, known causal factors in breast cancer etiology. METHODS AND RESULTS We examined the associations of green tea intake (<1 time/week, 1-6 times weekly, or 7+ times weekly) with urinary estrogens and estrogen metabolites (jointly EM) in a cross-sectional sample of healthy Japanese American women, including 119 premenopausal women in luteal phase and 72 postmenopausal women. We fit robust regression models to each log-transformed EM concentration (picomoles per mg creatinine), adjusting for age and study center. In premenopausal women, intake of green tea was associated with lower luteal total EM (P trend=0.01) and lower urinary 16-pathway EM (P trend=0.01). In postmenopausal women, urinary estrone and estradiol were approximately 20% and 40% lower (P trend=0.01 and 0.05, respectively) in women drinking green tea daily compared to those drinking<1 time/week. Adjustment for potential confounders (age at menarche, parity/age at first birth, body mass index, Asian birthplace, soy) did not change these associations. CONCLUSIONS Findings suggest that intake of green tea may modify estrogen metabolism or conjugation and in this way may influence breast cancer risk.