Premenopausal Equol Excretors Show Plasma Hormone Profiles Associated with Lowered Risk of Breast Cancer

Premenopausal Equol Excretors Show Plasma Hormone Profiles Associated with Lowered Risk of Breast Cancer1

Department of Food Science and Nutrition, University of Minnesota, St. Paul, Minnesota 55108 [A. M. D., B. E. M., X. X., M. S. K.], and the Department of Obstetrics and Gynecology, University of Rochester, Rochester, New York 14642 [W. R. P.]

Abstract

Increased urinary excretion of equol, a metabolite of the isoflavone daidzein, has been associated with a reduced risk of breast cancer. This risk reduction has generally been presumed to be a consequence of increased isoflavone consumption. However, only 30–40% of the population excretes more than trace amounts of equol, regardless of isoflavone intake. Accordingly, we hypothesized that the observed apparent protective effect of equol is at least in part attributable to hormonal differences between equol excretors and non-excretors, and that these differences are largely independent of isoflavone intake.

We measured plasma hormone and sex hormone binding globulin (SHBG) concentrations in 14 normally cycling premenopausal women during each of three diet periods in which they consumed differing isoflavone doses (0.15, 1.0, and 2.0 mg/kg of body weight/day) as a component of soy protein isolate. The plasma hormone and SHBG concentrations of equol excretors (n = 5) were then compared with those of the non-excretors (n = 9). Results showed that even at the lowest dose, urinary equol excretion values for excretors far exceeded those for non-excretors consuming the highest dose. At all doses, equol excretors generally had lower concentrations of estrone, estrone-sulfate, testosterone, androstenedione, dehydroepiandrosterone (DHEA), DHEA-sulfate, and cortisol and higher concentrations of SHBG and midluteal progesterone, a hormonal pattern overall consistent with lowered breast cancer risk. In conclusion, the association of equol excretion and lowered breast cancer risk may largely reflect the tendency of equol excretors to have more favorable hormonal profiles, as opposed to merely reflecting increased isoflavone intake. Equol may be a marker for the presence of colonic bacterial enzymatic activity that increases fecal steroid excretion. Alternatively, equol itself, even with very modest isoflavone intake, may exert beneficial effects on the regulation of endogenous hormones.

Footnotes

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↵1 Supported by NIH Grant CA-66016 and General Clinical Research Center Grant MO1-RR00400 from the National Center for Research Resources.
↵2 To whom requests for reprints should be addressed, at Department of Food Science and Nutrition, University of Minnesota, 1334 Eckles Avenue, St. Paul, MN 55108. Phone: (612) 624-9789; Fax: (612) 625-5272; E-mail: mkurzer{at}tc.umn.edu
↵3 The abbreviations used are: LH, luteinizing hormone; FSH, follicle stimulating hormone; DHEA, dehydroepiandrosterone; DHEA-S, DHEA sulfate; E₂, estradiol; E₁, estrone; E₁-S, estrone sulfate; SHBG, sex hormone binding globulin; EF, early follicular; MF, midfollicular; PO periovulatory; ML, midluteal.
- Accepted March 20, 1900.
- Received October 8, 1999.
- Revision received March 8, 1900.