Study: Low Free Testosterone Level May Up Alzheimer's Risk of Older Men

Older men with lower levels of free testosterone circulating in their bloodstreams could be at higher risk of developing Alzheimer's disease, according to a study reported in the January 27 issue of Neurology.

As men age, their testes produce less testosterone than they did during adolescence and early adulthood when production of this hormone peaks. Some testosterone remains freely circulating in the bloodstream, ciruclating into the brain and affecting nerve cells.

Study author Susan Resnick, an investigator in the NIA's Laboratory of Personality and Cognition, said the finding is a step forward in helping to understand the possible effects of sex hormones on the aging brain and other parts of the body

However, Resnick cautioned that much more research is needed before scientists can establish a causal relationship between low testosterone and Alzheimer's disease.

Resnick and her colleagues evaluated the testosterone levels of 574 men between the ages of 32 and 87, examining their free and total testosterone levels measured over an average of 19 years. Fifty-four of the men were later diagnosed with Alzheimer's.

The researchers found that for every 50 percent increase in the free testosterone index in the bloodstream, there was about a 26 percent decrease in the risk of developing Alzheimer's disease.

Resnick and her colleagues also found that free testosterone levels dropped more precipitously in men who later developed Alzheimer's disease. Men diagnosed with Alzheimer's disease had about half the levels of circulating free testosterone of men who didn't develop the disease. In some cases, the drop-off in free testosterone levels associated with Alzheimer's disease was detected up to a decade before diagnosis.

While prescription testosterone replacement therapy is available, Resnick said it may not be advisable for most older men because previous studies have linked it to heart disease and prostate cancer.

"We still have much to learn," Resnick said. "For now, testosterone therapy should not be considered an option for older men seeking to reduce their risk of Alzheimer's disease or to improve their memory and cognitive performance in general."

Other sources: National Institute on Aging