Soy isoflavones exert modest hormonal effects in premenopausal
women
Soy isoflavones exert modest hormonal effects in premenopausal
women.
Duncan AM, Merz BE, Xu X, Nagel TC, Phipps WR, Kurzer MS
J Clin Endocrinol Metab 1999 Jan 84:1 192-7
Abstract
Soy isoflavones are hypothesized to be responsible for changes in
hormone action associated with reduced breast cancer risk. To test this
hypothesis, we studied the effects of isoflavone consumption in 14
premenopausal women.
Isoflavones were consumed in soy protein powders and provided
relative to body weight (control diet, 10 +/- 1.1; low isoflavone diet,
64 +/- 9.2; high isoflavone diet, 128 +/- 16 mg/day) for three
menstrual cycles plus 9 days in a randomized cross-over design.
During the last 6 weeks of each diet period, plasma was collected
every other day for analysis of estrogens, progesterone, LH, and FSH.
Diet effects were assessed during each of four distinctly defined
menstrual cycle phases.
Plasma from the early follicular phase was analyzed for androgens,
cortisol, thyroid hormones, insulin, PRL, and sex hormone-binding
globulin.
The low isoflavone diet decreased LH (P = 0.009) and FSH (P = 0.04)
levels during the periovulatory phase. The high isoflavone diet
decreased free T3 (P = 0.02) and dehydroepiandrosterone sulfate (P =
0.02) levels during the early follicular phase and estrone levels
during the midfollicular phase (P = 0.02). No other significant changes
were observed in hormone concentrations or in the length of the
menstrual cycle, follicular phase, or luteal phase.
Endometrial biopsies performed in the luteal phase of cycle 3 of
each diet period revealed no effect of isoflavone consumption on
histological dating.
These data suggest that effects on plasma hormones and the menstrual
cycle are not likely to be the primary mechanisms by which isoflavones
may prevent cancer in premenopausal women.
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