For how we live.
Researchers searched in four languages across three engines. One in ten clinics said it would prescribe testosterone to men with normal levels; one in five claimed it cuts cardiovascular risk.
The randomised evidence in older men found a moderate effect on sexual function and none on vitality or walking. A 5,246-man safety trial cleared it on heart attacks and found more fractures.
Two datasets report an age-independent fall in men's testosterone across birth cohorts. A separate study of nine thousand men found much of the variation between cohorts came from the tests themselves.