Doctors have noted for some time that low levels of
testosterone in older men are
associated with a number of signs and symptoms of aging. These include fatigue,
an inability to concentrate, lowered libido and, for men with central adiposity
or excess fat around their waists, an increased risk for diabetes.
One long-term study of older men is being done through the 
University of California at San Diego. It has followed men from the
town of Rancho Bernardo since the early 70s. Twenty years ago, these men had a
thorough medical exam that included taking blood samples to measure testosterone
levels.
Model of the Testosterone structure
"We had
800 men that we measured the testosterone on, and they were followed yearly by
mailers," says Dr. Gail Laughlin, one of the researchers with the study. "Every
four years these men came back to the clinic and their health was assessed in
various ways. "
The researchers obtain death certificates on a regular basis for men in the
study who have died.
Laughlin says a 20-year analysis showed that men with lower levels of
testosterone over time had a 23 percent greater chance of death than their
contemporaries with normal levels of the reproductive hormone.
"We looked first to see if it could be explained completely by differences in
either body size or central adiposity or lifestyle characteristics including
physical activity, smoking and alcohol consumption," she says. "None of these
factors explain the association."
Laughlin says at the same time, men who had higher than normal levels of
testosterone did not live any longer than men with normal levels.
She stresses that the lesson from this study should not be that men go out
and start taking testosterone as they age. "This is an observational study, and
all we have found is an association," Laughlin says. "Until we can do the
randomized placebo controlled trials, we don't even know that testosterone is
safe for men."
Laughlin says her group is applying for funding to perform just such a trial.
She recently presented her research to The Endocrine Society and an article
based on the findings will be published later this year.
testosterone :睾丸激素
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