Boston , MA — About a million men are turning to testosterone therapy in hopes of restoring vitality and slowing the aging process. Boosting testosterone makes sense for men with low hormone levels. But for men with normal levels, little is known about the long-term effects of testosterone therapy on the heart, blood vessels, and other parts of the body.

By age 60, about one in five men have testosterone levels lower than what's normal for younger men, though no one knows if these levels are low for men their age. According to the April Harvard Heart Letter , this is just one of many things that needs to be discovered about the effects of testosterone therapy on men's health. One gray area is how daily doses of the hormone affect the heart, blood vessels, and circulation. Some studies suggest that testosterone can lower blood pressure, increase levels of HDL (good) cholesterol, and decrease the chances of developing atherosclerosis or diabetes. If this paints a positive, why-not-start-today picture of testosterone therapy, the recent flip-flop on postmenopausal hormone therapy in women should raise a red flag.

According to the Harvard Heart Letter editors, men shouldn't be taking testosterone unless their bodies aren't making enough of the hormone. Tip-offs include fatigue, muscle weakness, dwindling interest in sex, osteoporosis, or a suspicious bone fracture. Men whose testosterone levels are in the normal range should approach hormone therapy as an experimental treatment, aware of both the possible benefits and potential harm, until more is known about its long-term effects.

Related Information:

• Medical Memo: Testosterone and the heart: Another look  More • Not enough test in testosterone  More • Hormone replacement, the male version  More • Women's Hormones: Testosterone, the other female hormone  More