Associations of Urinary Equol Level and Equol-Producer Status with Endogenous Sex Hormone Levels in Premenopausal Japanese Women.

The potential protective effects of soy isoflavones against breast cancer have been suggested. Equol, the end product of daidzein by intestinal bacteria, is superior to other isoflavones in its estrogenic activity. However, not all humans can produce equol. We cross-sectionally assessed the associations between equol-excretion status and endogenous sex hormone levels relevant to the etiology of breast cancer in premenopausal Japanese women. Fasting plasma concentrations of estradiol, estrone, testosterone, dehydroepiandrosterone (DHEA) sulfate, sex hormone-binding globulin, follicle-stimulating hormone (FSH), and luteinizing hormone (LH) were measured in 348 premenopausal women with regular menstrual cycles. After controlling for covariates, urinary equol level was not significantly associated with the levels of any hormone. To approximate the ability to convert daidzein to equol, equol-producer status was defined among 141 women with urinary daidzein levels of 10 nmol/mg creatinine or higher. Among them, 30.5% had detectable levels of equol (equol producers). The plasma estrone level was significantly lower by 21.6% in equol producers than in non-producers. These data suggest that the ability to produce equol, but not equol itself, may be associated with the hormonal profile of premenopausal women. Further studies on factors related to equol production are needed.