Dietary isoflavones affect sex hormone-binding globulin levels in postmenopausal women

The studies presented in this report were designed to further investigate t he causal association between phytoestrogen action and increase in sex horm one-binding globulin (SHBG) levels. Phytoestrogens include isoflavones that bind to estrogen receptors and therefore exert estrogenic action. This stu dy included 20 postmenopausal women that ingested 30 g soy milk daily for 1 0 weeks. Plasma concentrations of isoflavones and SHBG were measured. Total isoflavones significantly increased from 0.014 +/- 0.01 mu mol/L (baseline ) to 0.53 +/- 0.19 mu mol/L, and paired responses showed that some subjects clearly increased their SHBG levels. The percent change in SHBG showed a p ositive correlation with phytoestrogen concentration; all women who had cir culating phytoestrogen levels above 0.6 mu mol/L increased by at least 30% their SHBG values. Results suggest that phytoestrogens may significantly in crease SHBG in subjects whose SHBG concentrations are in the low end of the concentration range.