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.
|
