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

Abstract

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.

• Authors: Mandeep K Virk-Baker, Stephen Barnes, Helen Krontiras, Tim R Nagy
• Journal: Nutrition research (New York, N.Y.) (Nutr Res) Vol. 34 Issue 2 Pg. 116-25 (Feb 2014) ISSN: 1879-0739 [Electronic] United States
• PMID: 24461312 (Publication Type: Journal Article, Research Support, N.I.H., Extramural, Research Support, Non-U.S. Gov't)
• Copyright: Published by Elsevier Inc.

Chemical References

• Estrogen Receptor beta
• Isoflavones
• Phytoestrogens
• Equol

Topics

• Aged
• Biological Availability
• Biopsy
• Breast (pathology)
• Breast Neoplasms (etiology, metabolism)
• Cross-Sectional Studies
• Diet
• Dietary Supplements
• Equol (biosynthesis, metabolism, urine)
• Estrogen Receptor beta (metabolism)
• Feeding Behavior
• Female
• Humans
• Isoflavones (administration & dosage, pharmacology)
• Middle Aged
• Odds Ratio
• Phytoestrogens (administration & dosage, pharmacology)
• Postmenopause
• Soy Foods
• Soybeans (chemistry)
• United States