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Declining testosterone might put men at risk for Alzheimer's High levels could afford protection, study suggests

By Kathleen Fackelmann, the USA Today

January 27, 2004

Low levels of the male sex hormone testosterone may put healthy men at risk of developing Alzheimer's years later, a new study suggests.

The report, released today in the journal Neurology, provides yet another clue into the factors that influence the development of Alzheimer's, a degenerative brain disease that afflicts 4.5 million people in the USA .

Susan Resnick at the National Institute on Aging, part of the National Institutes of Health, and her colleagues analyzed data from 574 men ages 32 to 87 who had participated in the Baltimore Longitudinal Study of Aging. The team measured levels of ''free'' testosterone in the blood. Free testosterone is not attached to a protein and thus is able to interact with brain cells -- and possibly protect them.

The team also evaluated the men for signs of Alzheimer's, an incurable disease that leads to memory problems and ultimately death. During the 19-year study, 54 men received a diagnosis of Alzheimer's.

The researchers found that higher levels of free testosterone seemed to protect men from Alzheimer's. The team reports that for every 50% increase in free testosterone in the blood, there was a 26% reduction in the risk of developing the disease.

Testosterone usually declines with age, but the team found that men who later developed Alzheimer's had testosterone levels that fell dramatically, in most cases below what is considered normal. By the end of the study, men with Alzheimer's had blood levels of testosterone that were half the levels of the men who remained healthy.

In some cases, the drop in testosterone was detected up to a decade before the men were diagnosed with Alzheimer's.

Testosterone might protect the brain by preventing beta amyloid, an abnormal sticky substance, from clumping to form the senile plaque that is at the heart of Alzheimer's, says Eva Hogervorst, a dementia researcher at Oxford University in England who wrote an accompanying editorial in the journal.

Estrogen might protect the brain in the same way, says Sam Gandy, a spokesman for the Alzheimer's Association in Chicago . But he and others warn that the final story is likely to be complicated. A recent study suggested that estrogen might increase the risk of dementia in older women.

About 800,000 men in the USA already take testosterone in the hopes that the sex hormone will restore a sluggish libido or improve memory, the editorial says. That's risky, though: The sex hormone has been linked to stroke and might increase the risk of prostate cancer, the second leading cause of cancer death among men.

''We do not recommend that men take testosterone to protect against Alzheimer's,'' Resnick says.