Daidzein-metabolizing phenotypes in relation to mammographic breast density among premenopausal women in the United States

Background Mammographic breast density is an established marker of breast cancer risk, and is hormonally sensitive. Studies suggest that production of the daidzein metabolites equol and O-Desmethylangolensin (ODMA) may be associated with hormones and hormonally mediated factors, but few studies have assessed relationships between the capacity to produce these metabolites and breast density. Objective To evaluate the relationship between equol- and ODMA-producer phenotypes and breast density in premenopausal women in the United States. Design Two hundred and three women attended a clinic visit and 200 provided a urine sample following a 3 day soy challenge. Samples were analyzed for isoflavones by GC-MS to determine daidzein-metabolizing phenotypes. Percent density on recent (< 14 month prior to their clinic visit) mammograms was assessed by one reader using a computer-assisted method. Multiple regression analysis was used to assess relationships between the production of equol and ODMA and breast density. Results 55(27.5%) and 182(91%) women were classed as equol- and ODMA-producers (> 87.5 ng/ml urine), respectively. In unadjusted and adjusted analyses, there were no differences in breast density between producers and non-producers of either equol or ODMA (P > 0.05). Conclusion In this population of low-soy consuming premenopausal women, there were no associations between daidzein-metabolizing phenotypes and breast density, suggesting that these phenotypes per se do not influence premenopausal breast density.