Soy isoflavones improve bone metabolism in postmenopausal Japanese women

1. This study examines whether the supplementation of isoflavones (ISO) exerts beneficial effects on serum and urinary biomarkers of bone metabolism. 2. A total of 102 women were randomly assigned to three groups taking either ISO (40 mg) tablets, tablets containing vitamins C (25 mg) and E (5 mg) (V) or placebo tablets (vehicle only) (P) daily for 4 weeks, in a double-blind parallel placebo controlled design. 3. Among the 67 women who completed the study (24 on ISO, 24 on V, 19 on P), only ISO tablets were proven to decrease significantly urinary deoxypyridinoline (Dpd) excretion (P < 0.05 vs before), a specific biomarker of bone resorption, but there was no significant difference in serum bone gamma-carboxyglutamic acid-containing protein (BGP), a specific serum biomarker of bone formation. 4. Among the 67, 25 women were postmenopausal (8 on ISO, 12 on V, 8 on P) and only ISO tablets decreased significantly urinary Dpd excretion (P < 0.05 vs before) in them. The reduction rate of Dpd in ISO group was also significantly greater than that in P group (P < 0.01). 5. Dietary supplementation of vitamins C 25 mg and E 5 mg did not affect urinary Dpd.