Researchers at the National Institute on Aging, part of the National Institutes of Health, analyzed data from 574 men, ages 32 to 87.
During the 19-year study, 54 men received a diagnosis of Alzheimer's, USA Today reported Tuesday.
The researchers found signs that men with higher percentages of "free" testosterone -- testosterone in the blood not attached to protein -- might have a greater protection against the disease. The testosterone that flows through the brain may help prevent the cells from deteriorating, researchers said.
A spokesman for the Alzheimer's Association in Chicago said some researchers speculate estrogen performs a similar function in the brains of women.