Many middle-aged men find their waistlines expanding and their sex drive shrinking, symptoms a new study out Wednesday suggests can be traced to a hormone deficiency -- but not the one you might imagine.

Previously, a drop in testosterone production might have been suspected as the culprit, but researchers said a decline in estrogen may be part of the problem.

"This study establishes testosterone levels at which various physiological functions start to become impaired,...read more here: Waistlines expanding, sex drive shrinking