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The problems observed were concerning enough to cause the researchers to put an early stop to the study, which is published in the July 1 issue of the New England Journal of Medicine.
However, the trial was a small one and volunteers were older men with diabetes, cardiovascular disease and other problems, so whether or not these adverse events would affect the larger population of men taking testosterone therapy is still an open question.
Furthermore, the testosterone doses used in this study were higher than often seen in doctors' offices and other trials, the authors noted.
"These results were a caution flag but not a red light about stopping treatment," said Dr. Evan Hadley, director of the division of geriatrics and clinical gerontology at the U.S. National Institute on Aging, which funded the trial. "The men in this study differed from others in testosterone trials because they were older and frailer. Many of them had chronic diseases. We cannot draw broader conclusions in many different populations of men."
Testosterone supplementation remains a controversial therapy.
"Testosterone is currently not approved for the treatment of older men with mobility problems or frailty, even though there is considerable off-label use of testosterone by older men with low testosterone levels," noted senior study author Dr. Shalender Bhasin. "Given the findings of this research study, older patients and their physicians should carefully weigh the risks of testosterone therapy in their treatment decisions."
Testosterone therapy is approved and has been shown to be effective in men with hypogonadism (low testosterone levels), which some have dubbed male menopause, or "andropause." However, a study published in the same journal earlier this month determined that the number of men actually suffering from the condition is probably much less than previously believed - only about 2% of men aged 40 to 80.
This study was designed to determine if testosterone could improve older men's ability to get around, given that the hormone has already been shown to boost muscle strength.
Just over 200 men aged 65 or older with low testosterone levels and mobility problems were randomly assigned to receive testosterone gel or a placebo daily for six months.
The trial was discontinued at the end of 2009 when researchers found that 23 men in the testosterone group had had cardiovascular problems including heart attacks and hypertension, compared with only five in the placebo arm. Participants taking testosterone also had more respiratory and skin-related side effects.
The men in the testosterone arm of the study did see gains in muscle strength and their ability to climb stairs, said Bhasin, who is chief of the division of endocrinology, diabetes and nutrition at Boston University School of Medicine.
But, he added, "these potentially beneficial effects on muscle strength were mitigated by the serious cardiovascular adverse events in men assigned to testosterone arm of the study."
Six other NIA-funded trials on testosterone are continuing, Hadley said.
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SOURCES: Shalender Bhasin, M.D., chief, section of endocrinology diabetes and nutrition, Boston University School of Medicine; Evan Hadley, M.D., director, division of geriatrics and clinical gerontology, National Institute on Aging; July 1, 2010, New England Journal of Medicine