S-(-)equol producing status not associated with breast cancer risk among low isoflavone-consuming US postmenopausal women undergoing a physician-recommended breast biopsy.
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.
Department of Nutrition Sciences, University of Alabama at Birmingham, Birmingham, AL, USA. Electronic address: mandeep.virk-baker@nih.gov.
Mandeep K
MK
Virk-Baker
Department of Pharmacology and Toxicology, University of Alabama at Birmingham, Birmingham, AL, USA; The UAB Comprehensive Cancer Center, Birmingham, AL, USA. Electronic address: sbarnes@uab.edu.
Stephen
S
Barnes
The UAB Comprehensive Cancer Center, Birmingham, AL, USA; Department of Surgery, Surgical Oncology, University of Alabama at Birmingham, Birmingham, AL, USA. Electronic address: helen.krontiras@ccc.uab.edu.
Helen
H
Krontiras
Department of Nutrition Sciences, University of Alabama at Birmingham, Birmingham, AL, USA; The UAB Comprehensive Cancer Center, Birmingham, AL, USA. Electronic address: tnagy@uab.edu.
Tim R
TR
Nagy
D000368:Aged; D001682:Biological Availability; D001706:Biopsy; D001940:Breast / Q000473:pathology*; D001943:Breast Neoplasms / Q000209:etiology* / Q000378:metabolism; D003430:Cross-Sectional Studies; D004032:Diet; D019587:Dietary Supplements; D060754:Equol / Q000096:biosynthesis* / Q000378:metabolism / Q000652:urine; D047629:Estrogen Receptor beta / Q000378:metabolism; D005247:Feeding Behavior; D005260:Female; D006801:Humans; D007529:Isoflavones / Q000008:administration & dosage* / Q000494:pharmacology; D008875:Middle Aged; D016017:Odds Ratio; D048789:Phytoestrogens / Q000008:administration & dosage* / Q000494:pharmacology; D017698:Postmenopause; D045730:Soy Foods; D013025:Glycine max / Q000737:chemistry*; D014481:United States
D047629:Estrogen Receptor beta; D007529:Isoflavones; D048789:Phytoestrogens; D060754:Equol
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