(CBS News) Symptoms of so-called "male menopause" may be triggered not only by declines in testosterone, but in the female hormone estrogen as well, according to a new study in the New England Journal of Medicine.
The study of 400 men ages 20 to 50 found that estrogen in men is important for keeping fat down and testosterone is important for muscle size and strength -- and that both are involved with sexual desire, Dr. Abraham Morgentaler, an associate clinical professor of urology at Harvard Medical School, explained on "CBS This Morning."
When researchers lowered estrogen in the study, men got more body fat and when estrogen was higher, they had less body fat. And as for sexual function, the combination of testosterone and estrogen was much better for sexual desire and functioning than testosterone alone.
"What this study showed is what happens between testosterone and estrogen in the male body," Morgentaler said. "As testosterone levels go down as men get older, estrogen levels go down, too. Estrogen actually comes from testosterone in men. And when it goes down, we have two problems then with the low testosterone and low estrogen. It affects sex drive, muscle, fat."
So should men be taking estrogen, as some men take supplements for low testosterone?
Morgentaler said, "The good news is men don't have to take more than one thing because, if you have low testosterone and we treat you with testosterone, some of that actually turns into estrogen, so we actually get both of the effects. And what we got out of the study is we finally were able to separate out what each part was doing, what testosterone was doing and what estrogen was doing.
He continued, "The thing that really blows me away is this idea that estrogen, the female hormone, is necessary for guys and sex drive. You need certain amounts of (estrogen) for it to work. So maybe men and women, maybe we're not so different after all."
For more on the study, watch Morgentaler's full "CTM" interview above.