There are several biologic mechanisms whereby
coffee might reduce
breast cancer risk.
Caffeine and
caffeic acid, major
coffee constituents, have been shown to suppress mammary
tumor formation in animal models and to inhibit DNA methylation in human
breast cancer cells, respectively.
Coffee may also reduce risk through decreasing
inflammation and influencing
estrogen metabolism. However, epidemiologic studies have been inconsistent and few studies have examined the association by
estrogen and
progesterone receptor (ER/PR) status. We evaluated
coffee intake for its effect on incident
breast cancer in the National Institutes of Health-AARP Diet and Health Study cohort, which included 198,404 women aged 50-71 with no history of
cancer, who in 1995-1996 completed a questionnaire capturing usual
coffee intake over the past year. State
cancer registry and mortality index linkage identified 9,915 primary incident
breast carcinomas through December 2006; available information on
hormone receptor (HR) status identified 2,051 ER+/PR+ and 453 ER-/PR-
cancers. In multivariable proportional hazards models,
coffee intake was not associated with
breast cancer risk (p-value for trend = 0.38; relative risk = 0.98, 95% confidence interval: 0.91-1.07, for four or more cups per day as compared to women who never drank
coffee), and results did not vary by body mass index or history of benign breast biopsy (p-value for interaction > 0.10). We found no evidence of a relationship with either caffeinated or decaffeinated
coffee. Null findings persisted for risk of both HR-positive and -negative breast
cancers. These findings from a large prospective cohort do not support a role of
coffee intake in breast
carcinogenesis.