Women who take estrogen pills after menopause are less likely to develop Alzheimer's disease than women who don't. Now, test tube experiments with nerve cells suggest that buffing up levels of testosterone might similarly protect aging men from the degenerative disease.
Alzheimer's afflicts about 4 million men and women in the United States alone. As people live even longer, that count is predicted to jump to 14 million by mid-century. As the disease develops, senile plaques--clumps of proteins called b-amyloid peptides--accumulate in brain areas associated with learning and memory, probably killing nearby neurons. Even in healthy brains, enzymes are constantly chopping these short, sticky snippets of protein from a larger protein that sits on the surface of nerve cells. But in people with Alzheimer's, b-amyloid production is geared up.
Because estrogen supplements somehow protect women against Alzheimer's, neuroscientist Paul Greengard and his team at Rockefeller University in New York decided to see if testosterone could be just as valuable. Testosterone levels drop as men age, as does estrogen during menopause, and the hormones are structurally similar--suggesting that both may have a protective effect. The researchers took nerve cells from rat brains, soaked them with testosterone, estrogen, or other hormones, and measured the amounts of b-amyloid the cells churned out. In contrast to other compounds, testosterone and estrogen both reduced b-amyloid production--by 30% to 40% compared to untreated control cells--they report in the February 1 Proceedings of the National Academy of Sciences.
This kind of drop in b-amyloid is a "gigantic effect," says Alzheimer's expert Konrad Beyreuther of the Center for Molecular Biology in Heidelberg, Germany. He estimates that if the hormone treatment works as well in humans, it could delay onset of the disease by many years. But a lot of research will have to come before men start popping testosterone pills. For starters, Beyreuther cautions, testosterone increases the risk of heart disease and prostate cancer.