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.
"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.