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Study tracks symptoms in men as testosterone levels decline

| Sunday, Sept. 15, 2013, 5:30 p.m.

NEW YORK — Low testosterone production can reduce strength, muscle size and lean mass. If the testosterone isn't being converted to estrogen, men may experience an increase in body fat. And a deficiency of either can spark a decline in sexual function, according to a new study of hundreds of volunteers.

The research, published in the New England Journal of Medicine, appears at a time when testosterone supplements are being widely advertised to men in the United States, for example, in commercials urging them to be treated for “Low T.”

Unlike new drugs that are approved for a specific problem, testosterone is subject to “surging overuse from off-label prescribing for diverse unproven indications, including use in older men as an anti-aging or sexual tonic and in younger men for bodybuilding or doping,” even though the way it works is not well understood, David Handelsman of the University of Sydney wrote in a Journal editorial.

“The bottom line is there are tens of millions who are aging and who are having their hormone levels changed,” said Dr. Joel Finkelstein of Massachusetts General Hospital in Boston, the lead study author. “We don't know which men should be treated, whether it's effective and whether it's actually safe.”

The study was an attempt to separate the effects of testosterone and estrogen — most of which is made by the body from testosterone — on men's sexual function, strength, muscle size and lean and fat mass, and to discover how much testosterone is needed for health.

“This study allows us to begin to be more sensible about the diagnosis and treatment of low testosterone,” said Dr. Bradley Anawalt, chairman of The Endocrine Society's Hormone Health Network. He was not part of the research.

“It shows that testosterone has different effects at different levels for different tissues,” he said.

A group of 400 healthy volunteers were injected with a drug to shut down natural production of both testosterone and estrogen, then for 16 weeks, they were given varying doses of testosterone gel, placebo gel and anastrozole to prevent testosterone from being converted to estradiol, a form of estrogen.

Among the findings, sexual desire dropped progressively with lower testosterone levels.

Testosterone levels had to be extremely low before erectile dysfunction appeared. If estrogen production fell, it had an effect on sexual function regardless of how much testosterone the man produced.

Testosterone levels had to be very low before the researchers saw declines in leg strength, the size of the thigh muscle and lean body mass.

When estrogen production was blocked, there was an increase in body fat regardless of how much testosterone was in the blood. When it was not blocked, only a mild reduction in testosterone was enough to increase body fat.

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