Aromatase inhibition increased testosterone, decreased estradiol but didn't prevent bone loss.

Researchers conducted a one-year, randomized, double-blind, placebo-controlled trial that assessed the effects of aromatase inhibition on bone mineral density in older men. Sixty-nine men aged 60 years or older with borderline or low testosterone levels and symptoms of hypogonadism were randomly assigned to 1-mg anastrozole (Arimidex, AstraZeneca) or placebo daily.

Anastrozole increased serum testosterone levels from 319 ng/dL at baseline to 524 ng/dL at three months and a declined slightly to 474 ng/dL at one year (P<.0001) — an overall increase of about 50%.

This paper presents evidence that it is estrogen, not androgen, that preserves bone mass in men as well as women. This estrogen-deficiency bone loss was previously reported in men who have an aromatase deficiency and are unable to convert androgen to estrogen. It would be interesting to see in aging men whether there is a naturally occurring decrease in conversion of androgen to estrogen which might correspond, at least partially, to the bone loss seen in the older man.