Effects of soy isoflavones on markers of bone turnover in premenopausal and postmenopausal women

Soy isoflavones are hypothesized to exert hormonal effects in women and thu s may play a role in bone metabolism throughout life. In 2 randomized, cros s-over studies, 14 pre- and 17 postmenopausal women were given 3 soy protei n isolates containing different amounts of isoflavones [control, 0.13; low isoflavone (low-iso), 1.00; and high-iso, 2.01 mg/kg body wt day, averaging 8, 65, and 130 mg/day, respectively], for over 3 months each. Food records , blood samples, and 24-h urine collections were obtained throughout the st udies. The endpoints evaluated included plasma or serum concentrations of b one-specific alkaline phosphatase, osteocalcin, insulin-like growth factor- I (IGFI), IGF binding protein-3 (IGFBPS), and urine concentrations of deoxy pyridinoline cross-links and carboxy-terminal telopeptide of type I collage n. In premenopausal women, IGFI and IGFBP3 concentrations were increased by the low-iso;diet, and deoxypyridinoline cross-links was increased by bath the low- and high-iso diets during certain phases of the menstrual cycle. I n postmenopausal women, bone-specific alkaline phosphatase was decreased by both the low- and high-iso diets, and there were trends toward decreased o steocalcin, IGFI, and IGFBP3 concentrations with increasing isoflavone cons umption. Although say isoflavones do affect markers of bone turnover, the c hanges observed were of small magnitude and not likely to be clinically rel evant. These data do not support the hypothesis that dietary isoflavones pe r se exert beneficial effects on bone turnover in women.