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.
The Urology Care Foundation has more on low testosterone.
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