title: Evidence for an association of dietary flavonoid intake with breast cancer risk by estrogen receptor status is limited.
abstract: BACKGROUND
  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 associations with the more aggressive estrogen receptor (ER)-negative (ER-) tumors.
  
  
  OBJECTIVE
  We examined the associations between 7 subclasses of dietary flavonoids and invasive postmenopausal breast cancer risk overall and by ER status in a U.S. prospective cohort.
  
  
  METHODS
  In 1999-2000, 56,630 postmenopausal women completed detailed self-administered questionnaires, among whom 2116 invasive breast cancers were verified during a mean follow-up period of 8.5 y. Cox proportional hazards regression was used to calculate multivariable-adjusted HRs and 95% CIs.
  
  
  RESULTS
  Total flavonoid intake was not associated with breast cancer risk. However, there was a modest 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 ER- 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.
  
  
  CONCLUSIONS
  The inverse association of flavan-3-ol intake with ER- but not ER+ breast cancer is consistent with other studies that suggest a beneficial role of plant-based diets in ER- breast cancer risk.
authors.affiliation: Epidemiology Research Program, American Cancer Society, Atlanta, GA; and ying.wang@cancer.org.
authors.forename: Ying
authors.initials: Y
authors.lastname: Wang
authors.affiliation: Epidemiology Research Program, American Cancer Society, Atlanta, GA; and.
authors.forename: Susan M
authors.initials: SM
authors.lastname: Gapstur
authors.affiliation: Epidemiology Research Program, American Cancer Society, Atlanta, GA; and.
authors.forename: Mia M
authors.initials: MM
authors.lastname: Gaudet
authors.affiliation: Friedman School of Nutrition Science and Policy and.
authors.forename: Julia J
authors.initials: JJ
authors.lastname: Peterson
authors.affiliation: School of Medicine and Jean Mayer USDA Human Nutrition Center on Aging, Tufts University, Boston, MA.
authors.forename: Johanna T
authors.initials: JT
authors.lastname: Dwyer
authors.affiliation: Epidemiology Research Program, American Cancer Society, Atlanta, GA; and.
authors.forename: Marjorie L
authors.initials: ML
authors.lastname: McCullough
mesh_terms: D000368:Aged; D015992:Body Mass Index; D001835:Body Weight; D001943:Breast Neoplasms / Q000473:pathology / Q000517:prevention & control*; D004032:Diet; D005260:Female; D005419:Flavonoids / Q000008:administration & dosage*; D005500:Follow-Up Studies; D006801:Humans; D017698:Postmenopause / Q000187:drug effects; D016016:Proportional Hazards Models; D011446:Prospective Studies; D011960:Receptors, Estrogen / Q000378:metabolism*; D012307:Risk Factors; D011795:Surveys and Questionnaires
chemical_list: D005419:Flavonoids; D011960:Receptors, Estrogen