ASSOCIATION OF COFFEE, GREEN TEA, AND CAFFEINE INTAKES WITH SERUM CONCENTRATIONS OF ESTRADIOL AND SEX HORMONE-BINDING GLOBULIN IN PREMENOPAUSAL JAPANESE WOMEN

Caffeine intake has been proposed to influence breast cancer risk. Its effect may be mediated by hormonal changes. The relationships between caffeine-containing beverages (coffee, green tea, black tea, oolong t ea, and cola) and serum concentrations of estradiol and sex hormone-bi nding globulin were evaluated in 50 premenopausal Japanese women. Inta kes of caffeine and caffeine-containing beverages were assessed by a s emiquantitative food-frequency questionnaire. Blood samples were obtai ned from each woman on Days II and 22 of her menstrual cycle. High int akes of caffeinated coffee, green tea, and total caffeine were commonl y correlated with increasing sex hormone-binding globulin on Days II a nd 22 of the cycle after controlling for potential confounders [Spearm an correlation coefficients (r) ranged from 0.23 to 0.31]. Green tea b ut not caffeinated coffee intake was inversely correlated with estradi ol on Day II of the cycle (r = -0.32, p = 0.04). Although the effect o f caffeine cannot be distinguished from effects of coffee and green te a, consumption of caffeine-containing beverages appeared to favorably alter hormone levels associated with the risk of developing breast can cer.