Evidence for an Association of Dietary Flavonoid Intake with Breast Cancer Risk by Estrogen Receptor Status Is Limited1–3

Results from preclinical studies suggest that flavonoids, which are ubiquitous in plant-based diets, lower breast cancer risk. Epidemiologic studies of flavonoid intake and breast cancer risk, however, are limited, and few investigated asso-ciations with the more aggressive estrogen receptor (ER)–negative (ER2) tumors. We examined the associations be-tween 7 subclasses of dietary flavonoids and invasive postmenopausal breast cancer risk overall and by ER status in a U.S. prospective cohort. In 1999–2000, 56,630 postmenopausal women completed detailed self-administered questionnaires, amongwhom 2116 invasive breast cancers were verified during amean follow-up period of 8.5 y. Cox proportional hazards regression was used to calculate multivariable-adjusted HRs and 95 % CIs. Total flavonoid intake was not associated with breast cancer risk. However, therewas amodest inverse association between flavone intake and overall breast cancer risk (fifth vs. first quintile HR: 0.88; 95 % CI: 0.76, 1.01; P-trend = 0.04) and between flavan-3-ol intake and risk of ER2 breast cancer (for an increment of 40 mg/d; HR: 0.81; 95 % CI: 0.67, 0.97) but not for ER-positive (ER+) breast cancer risk. The inverse association of flavan-3-ol intake with ER2 but not ER+ breast cancer is consistent with other studies that suggest a beneficial role of plant-based diets in ER2 breast cancer risk. J. Nutr. doi: 10.3945/jn.114.196964