Coffee consumption and risk of endometrial cancer: a prospective study in Japan.

Coffee has been proposed to decrease the circulating insulin and estrogen levels, which are related to the development of endometrial cancer. However, few studies have prospectively assessed the association between coffee consumption and endometrial cancer. We conducted a population-based prospective cohort study in 53,724 Japanese women aged 40-69 years with no history of cancer at baseline in 1990-1994. We used Cox proportional hazards regression analysis to estimate the hazard ratio (HR) and 95% confidence interval (CI) of endometrial cancer incidence in relation to coffee consumption. All reported p values are 2-tailed. During the 15-year follow-up period, we documented 117 cases of endometrial cancer. Coffee consumption was significantly associated with a decreased risk of endometrial cancer. After adjustment for age, study area, body mass index, menopausal status, age at menopause for postmenopausal women, parity, use of exogenous female hormones, smoking status and by consumption of green vegetables, beef, pork and green tea, the multivariate HRs (95% CI) of endometrial cancer in women who drank coffee </=2 days/week, 3-4 days/week, 1-2 cups/day and >/=3 cups/day were 1.00, 0.97 (0.56-1.68), 0.61 (0.39-0.97) and 0.38 (0.16-0.91), respectively (p for trend = 0.007). In contrast, green tea consumption was not significantly associated with a reduced risk of endometrial cancer (p for trend = 0.22). The inverse association between coffee consumption and risk of endometrial cancer was consistently observed in subgroup analyses stratified by potential confounders. Coffee consumption may be associated with a decreased risk of endometrial cancer.