Detection of isoflavones in mouse tibia after feeding daidzein

Many studies suggest that diets rich in isoflavones protect against bone loss or slow the loss of bone mass that occurs because of estrogen withdrawal. Although in vitro studies have reported effects of isoflavones on bone cells, the presence of daidzein and/or equol in bone tissue in vivo has not been reported. The objective of this study was to determine if daidzein and equol were present in bone tissue (tibias) after feeding mice a diet containing purified daidzein. Sham mice (n = 9) received control diet, and ovariectomized mice were randomized to control diet (Ovx) (n = 9) or control diet containing 200 mg of daidzein/kg of diet (n = 8) for 12 weeks. At necropsy, tibias and serum were collected. Mice in the Daidzein group had significantly higher (P < .05) levels of both daidzein and equol in tibias than Sham and Ovx mice. Tibia levels of daidzein and equol were approximately five and four times higher, respectively, than the Sham and Ovx groups. Similarly, mice fed daidzein also had significantly higher (P < .05) serum daidzein and equol than the Sham and Ovx mice. In conclusion, feeding a level of daidzein that is attainable by dietary intervention alone results in a high level of both daidzein and equol in tibias. These findings suggest that daidzein and its metabolite, equol, have the potential to act directly on bone cells in vivo.