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- McMichael-Phillips DF,
Harding C, Morton M, Roberts SA, Howell A, Potten CS, Bundred
NJ
- Am J Clin Nutr 1998 Dec
68:6 Suppl 1431S-1435S
- Abstract
- A high dietary intake
of soy products (eg, as in Japan and Singapore) hasbeen associated
with a reduction in the incidence of breast cancer in premenopausal
women. Phytoestrogens present in soybeans inhibit human breast
cancer cell proliferation in vitro and breast cancer development
in animal models, but no data exist on the effects of phytoestrogens
on histologically normal human breasts. This study examines the
effects of dietary soy supplementation on the proliferation rate
of premenopausal, histologically normal breast epithelium and
the expression of progesterone receptor. Women (n = 48) with benign
or malignant breast disease were randomly assigned to receive
their normal diet either alone or with a 60-g soy supplement (containing
45 mg isoflavones) taken daily for 14 d. Biopsy samples of normal
breasts were labeled with [3H]thymidine to detect the number of
cells in S phase and were immunocytochemically stained for the
proliferation antigen Ki67. The phytoestrogens genistein, daidzein,
equol, enterolactone, and enterodiol were measured in serum samples
obtained before and after supplementation. Serum concentrations
of the isoflavones genistein and daidzein increased in the soy
group at 14 d. Results showed a strong correlation between Ki67
and the thymidine labeling index (r = 0.868, P < or = 0.001).
The proliferation rate of breast lobular epithelium significantly
increased after 14 d of soy supplementation when both the day
of menstrual cycle and the age of patient were accounted for.
Progesterone receptor expression increased significantly in the
soy group. Short-term dietary soy stimulates breast proliferation;
further studies are required to determine whether this is due
to estrogen agonist activity and to examine the long-term effects
of soy supplementation on the pituitary gland and breast.
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