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Premenopausal equol excretors show plasma hormone profiles associated with lowered risk of breast cancer [In Process Citation]
Authors: Duncan AM; Merz-Demlow BE; Xu X; Phipps WR Kurzer MS
Source: Cancer Epidemiol Biomarkers Prev 2000 Jun;9(6):581-6
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.