Testosterone Not the Whole Story in 'Male Menopause'
Estrogen also involved, researchers say, and 'low-T' diagnosis isn't clear-cut
That way, the researchers were able to pinpoint the levels at which testosterone loss spurred particular symptoms -- and whether estrogen played a key role in any of those problems.
In general, they found, increases in body fat and a waning interest in sex started to emerge at mild levels of testosterone deficiency. But muscle loss and erectile dysfunction were not seen until testosterone dropped lower -- around 200 ng/dL or below.
Finkelstein agreed that none of this answers the big question of whether testosterone replacement is a good thing. And the researchers still need to see whether their findings hold true in men older than 50 as well.
"This study is a step along the way in our understanding," Finkelstein said. "I would tell men to stay cautious and conservative" about testosterone therapy.
Amory said there are some men who benefit from testosterone therapy, which comes in the form of topical gels, patches and injections, and can cost up to $300 a month.
But they are the men whose testosterone levels are clearly low and causing problems. The difficulty, according to Amory, is when a man has a moderately low "T level" and a vague symptom such as fatigue -- which can have many causes.
Testosterone supplements have potential side effects, including acne and prostate enlargement. But maybe the biggest worry is that the long-range health effects are unknown.
"If a man asks me if this will raise his risk of heart disease 10 years from now, all I can say is, 'I don't know,'" Amory said. "We're flying a bit blind on this."
He and Finkelstein both pointed to the story of hormone replacement in women as a cautionary tale. Doctors once widely prescribed estrogen and progesterone to women as a way to ward off heart disease -- until a large U.S. trial found that older women given the hormones actually faced increased risks of blood clots, heart attack, stroke and breast cancer.
"We haven't had an analogous study in men yet," Amory said.