Flavonoid intake and breast cancer incidence and survival

Background. Flavonoids are phytochemicals found in a variety of foods that have demonstrated anti-carcinogenic properties in experimental studies. Two epidemiologic studies conducted in the Mediterranean have observed an inverse association between dietary intake of certain flavonoid classes and breast cancer incidence. However, it is unknown whether a similar association is evident among American women. Further, whether flavonoids affect breast cancer survival is unknown. We investigated whether dietary flavonoid intake influences breast cancer incidence and survival among a population-based cohort of American women. Methods. A population-based, case-control study was conducted among women ages 20-98 years who resided in Nassau and Suffolk counties in Long Island, New York. Cases were newly diagnosed with a first invasive breast cancer between August 1, 1996 and July 31, 1997; controls were identified using random digit dialing and Health Care Finance Administration rosters. Trained interviewers administered an in-person questionnaire to participants on known and suspected breast cancer risk factors. Participants also completed a self-administered food frequency questionnaire regarding their average frequency of food and beverage consumption in the prior 12 months. For those with known menopausal status, 1,434 breast cancer cases and 1,440 controls provided adequate dietary responses. Case medical records were obtained to assess tumor characteristics and initial course of treatment. Cases were followed-up through 2002. All-cause mortality (n = 173) and breast cancer-specific mortality (n = 113) were determined through the National Death Index. Results. Increasing intake of flavonols, flavones, flavan-3-ols, and lignans, as reported at the case-control interview, was associated with a reduced risk of incident post-menopausal breast cancer among Long Island women. All-cause mortality among post-menopausal women was reduced for intake of flavones and isoflavones and similar results were observed for breast cancer-specific mortality. Conclusion. Findings provide evidence for a beneficial effect of flavones, flavonols and lignans on breast cancer incidence among post-menopausal women. Results from the follow-up study indicate that mortality among post-menopausal breast cancer patients is reduced in association with high intake of flavones and isoflavones near the time of diagnosis. These findings suggest American women can consume sufficient levels of flavonoid-rich foods to benefit from their potential chemopreventive effects.