When testosterone aromatization into estradiol is blocked, bone mineral density decreases by 1.7%. Even though testosterone levels may increase with the use of an aromatization inhibitor such, as anastrozole, the estradiol reduction of more than 20% may lead to negative skeletal effects (decrease in bone mineral density). Estradiol levels…are a more robust…predictor of fracture risk in aging men (blocking estradiol leads to an increased fracture risk in aging men). Small reductions in estradiol levels appear to significantly increase rates of bone loss. High estradiol levels are necessary for optimal skeletal benefits. Estradiol not only prevented bone loss but also increased lean body mass and inhibited increased in fat mass. The findings in this paper indicate that aromatization of testosterone to estradiol may be critical not only for skeletal preservation but also for beneficial effects on body composition.