A landmark study suggests that testosterone treatment is no fountain of youth, finding mostly modest improvement in the sex lives, walking strength and mood of a select group of older men.
The results from a US government-funded study are the first solid evidence of whether these hugely popular supplements can help treat low sex drive and other symptoms sometimes blamed on ageing.
The researchers emphasised that the findings pertain only to use of testosterone gel by men 65 and older with low hormone levels and related symptoms; whether similar benefits would occur in younger men or with testosterone pills, patches or shots is unknown.
Lead author Dr Peter Snyder, a University of Pennsylvania hormone specialist, said it would be premature to recommend the treatment even for men like those studied.
"We still don't know everything we want to know," he said.
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The study involved almost 800 men 65 and older at 12 centres nationwide. All had low blood levels of testosterone, the main male sex hormone. They were randomly assigned to use testosterone gel or fake gel without hormones, rubbed daily on the skin for a year.
Improvement in sex lives was modest among the testosterone group, and the benefits in erectile function were less that what has been seen with Viagra and similar drugs.
The men on testosterone had slightly greater improvement in mood and walking strength than the other men, but there was no difference in energy boost between the two groups.
The research is among seven testosterone studies the National Institute on Aging launched in 2009 to examine the risks and benefits of testosterone supplements.
Testosterone levels typically decline with age.
Supplements are approved only for treating testosterone deficiency caused by certain medical conditions, such as problems with the testes, but they have become a multibillion-dollar industry, feeding on ageing men's desire to remain youthful.
The new research combines results from three of the government-funded studies.
Results are expected later from the four other studies, which tested the hormone's effects on mental function, bone density, heart function and anaemia.
The current results are in Thursday's New England Journal of Medicine.
The findings "bring some real rigor" to questions surrounding testosterone use and suggest that the treatment is "not a panacea" for age-related ills, said Dr Eric Orwoll, a physician-researcher at Oregon Health and Science University in Portland.
