Objective: Equol is a metabolite of the isoflavone daidzein and may play a critical role in preventing bone loss by soy isoflavones in postmenopausal women. However, results from clinical trials have not been published. The aim of this study was to investigate the effects of equol on bone metabolism and serum sex and thyroid hormone levels in postmenopausal Japanese women.
Methods: We performed a 1-year double-blind, randomized, placebo-controlled trial with natural S-equol supplements for 93 non-equol-producing menopausal Japanese women. Participants were randomly assigned to four groups receiving the following: placebo, 2 mg of equol supplement per day, 6 mg of equol supplement per day, and 10 mg of equol supplement per day.
Results: Equol intervention increased equol concentrations in serum and urine in a dose-dependent manner. Urinary deoxypyridinoline was significantly decreased, with a -23.94% change in the group that received 10 mg of equol supplement per day as compared with a -2.87% change in the group that received placebo after 12 months of intervention (P = 0.020). Thus, 10 mg/day of equol supplement markedly inhibited bone resorption. Treatment with 10 mg/day of equol prevented a decrease in bone mineral density in the entire body in postmenopausal women after 12 months. Sex and thyroid hormone concentrations in serum did not differ among the four groups after intervention.
Conclusions: These findings suggest that 10 mg/day of natural S-equol supplementation contributes to bone health in non-equol-producing postmenopausal women without adverse effects.