...Meaning of "low" and "normal" is unclear: Doctors don't exactly know what "low" is. "Normal" testosterone levels for any age are over 300 nanograms per deciliter. But the healthy range is large and spans between 250 and 1,100 nanograms per deciliter, said Neil Goodman, chairman of the hormone and reproductive medicine committee for the American Association of Clinical Endocrinologists.
"In general, if it's under 200, the guy really has a problem that needs to be worked on," said Goodman, a professor of medicine at the University of Miami. "It's the 200 to 300 range where no one can agree whether the symptoms are related to testosterone," said Goodman.
(Some men's bodies can't produce enough testosterone because their testes may be damaged or pituitary glands have been destroyed by infections or tumors. Chronic illness, stress, and alcoholism can also cause low testosterone. In these cases, prescription testosterone patches, injections or topical gel can help a man maintain strong muscles and bones and increase his sex drive.)
Replacement therapy to deal with expected, age-related testosterone decline is unproven: Testosterone therapy is still a "scientifically unproven method" for preventing or relieving the physical and psychological changes that men with age-appropriate testosterone levels experience later in life, according to a report by the Institute of Medicine. The Food and Drug Administration has not approved testosterone use ó or any over-the-counter products ó for those who want to improve their strength, athletic performance, physical appearance or to prevent aging.