S-(-)equol producing status not associated with breast cancer risk among low isoflavone-consuming US postmenopausal women undergoing a physician-recommended breast biopsy.

Academic Article


  • Soy foods are the richest sources of isoflavones, mainly daidzein and genistein. Soy isoflavones are structurally similar to the steroid hormone 17β-estradiol and may protect against breast cancer. S-(-)equol, a metabolite of the soy isoflavone daidzein, has a higher bioavailability and greater affinity for estrogen receptor β than daidzein. Approximately one-third of the Western population is able to produce S-(-)equol, and the ability is linked to certain gut microbes. We hypothesized that the prevalence of breast cancer, ductal hyperplasia, and overall breast pathology will be lower among S-(-)equol producing, as compared with nonproducing, postmenopausal women undergoing a breast biopsy. We tested our hypothesis using a cross-sectional study design. Usual diets of the participants were supplemented with 1 soy bar per day for 3 consecutive days. Liquid chromatography-multiple reaction ion monitoring mass spectrometry analysis of urine from 143 subjects revealed 25 (17.5%) as S-(-)equol producers. We found no statistically significant associations between S-(-)equol producing status and overall breast pathology (odds ratio [OR], 0.68; 95% confidence interval [CI], 0.23-1.89), ductal hyperplasia (OR, 0.84; 95% CI, 0.20-3.41), or breast cancer (OR, 0.56; 95% CI, 0.16-1.87). However, the mean dietary isoflavone intake was much lower (0.3 mg/d) than in previous reports. Given that the amount of S-(-)equol produced in the gut depends on the amount of daidzein exposure, the low soy intake coupled with lower prevalence of S-(-)equol producing status in the study population favors toward null associations. Findings from our study could be used for further investigations on S-(-)equol producing status and disease risk.
  • Published In

  • Nutrition Research  Journal
  • Keywords

  • AA, AS, African American, Asian American, BMI, Breast biopsy, Breast cancer, CI, Dietary soy isoflavones, Ductal hyperplasia, ER, ER+, ER–, FFQ, Food Frequency Questionnaire, LC-MRM-MS, OR, Postmenopausal women, S-(−)equol status, SSQ, Soy Screen Questionnaire, UAB, University of Alabama at Birmingham., body mass index, confidence interval, estrogen receptor, estrogen receptor negative, estrogen receptor positive, liquid chromatography–multiple reaction ion monitoring mass spectrometry, odds ratio, Aged, Biological Availability, Biopsy, Breast, Breast Neoplasms, Cross-Sectional Studies, Diet, Dietary Supplements, Equol, Estrogen Receptor beta, Feeding Behavior, Female, Humans, Isoflavones, Middle Aged, Odds Ratio, Phytoestrogens, Postmenopause, Soy Foods, Soybeans, United States
  • Digital Object Identifier (doi)

    Author List

  • Virk-Baker MK; Barnes S; Krontiras H; Nagy TR
  • Start Page

  • 116
  • End Page

  • 125
  • Volume

  • 34
  • Issue

  • 2