testosterone
Over-training suppresses testosterone production.
Abuse can lead to heart attacks, stroke, depression and infertility.
The largest study of testosterone replacement therapy is targeting older men who have lost their sex drive.
WHAT'S HAPPENING
There's good news and not-so-good news.
A new study suggests that hormones might just predict if men will be nurturing dads.
"It's too early to put this stuff in the water supply," one researcher says.
