Changes men experience as they age is not just the result of lowered testosterone levels, but lowered estrogen levels as well.
Researchers at Massachusetts General Hospital wanted to study which bodily functions or symptoms are associated with testosterone levels and which are associated with estrogen levels. Their study included over 300 men who all received a drug of the suppressed production of reproductive hormones. Then they were split into two groups and were randomly assigned a testosterone or placebo gel. After a 16 week period, researchers found testosterone levels regulate less body mass and muscle mass, while estrogen levels regulate fat accumulation. Both hormones were shown to regulate sexual function. The results could impact testosterone replacement therapy in the future.