The relation between consumption of coffee, tea and caffeine and risk of breast cancer remains unsettled. We examined data from a large, long-term cohort study to evaluate whether high intake of coffee and caffeine is associated with increased risk of breast cancer. This was a prospective cohort study with 85,987 female participants in the Nurses' Health Study. Consumption of coffee, tea and caffeine consumption was assessed in 1980, 1984, 1986, 1990, 1994, 1998 and the follow-up continued through 2002. We documented 5,272 cases of invasive breast cancer during 1,715,230 person-years. The multivariate relative risks (RRs) of breast cancer across categories of caffeinated coffee consumption were: 1.0 for <1 cup/month (reference category), 1.01 (95% confidence interval: 0.92-1.12) for 1 month to 4.9 week, 0.92 (0.84-1.01) for 5 week to 1.9 days, 0.93 (0.85-1.02) for 2-3.9 days, 0.92 (0.82-1.03) for >or=4 cups per day (p for trend = 0.14). Intakes of tea and decaffeinated coffee were also not significantly associated with risk of breast cancer. RRs (95% CI) for increasing quintiles of caffeine intake were 1.00, 0.98 (0.90-1.07), 0.92 (0.84-1.00), 0.94 (0.87-1.03) and 0.93 (0.85-1.01) (p for trend = 0.06). A significant inverse association of caffeine intake with breast cancers was observed among postmenopausal women; for the highest quintile of intake compared to the lowest RR 0.88 (95% CI = 0.79-0.97, p for trend = 0.03). We observed no substantial association between caffeinated and decaffeinated coffee and tea consumption and risk of breast cancer in the overall cohort. However, our results suggested a weak inverse association between caffeine-containing beverages and risk of postmenopausal breast cancer.
(c) 2008 Wiley-Liss, Inc.