"What I think is happening, and what a lot of other people think is happening, is that people develop small strokes that are not significantly big enough to disable you, but cumulatively knock your [mental] condition down," Howard said.
Mini-strokes are not that uncommon, he said. Starting at age 55, about 10 percent of people who report never having had a stroke show evidence of one when they undergo brain scans, he said. The number grows to about half by age 80. Those mini-strokes create holes in the brain where blood flow has been restricted.
Dr. Argye Hillis, an associate professor of neurology at Johns Hopkins University, said the study "provides the strongest evidence of the association between the risk factors and cognitive decline."
It's not clear, though, if the risk factors directly cause brain deterioration or if they're part of a larger complex of conditions, she said. For example, people with diabetes and high blood pressure may be prone to have inflammation of the blood vessels, leading to mini-strokes, she said.
Other factors, such as a sedentary lifestyle, could also play a part, she said.
Learn more about stroke from the National Institutes of Health.
SOURCES: George Howard, Dr.P.H., professor and chairman, biostatistics, University of Alabama in Birmingham; Argye Hillis, M.D., associate professor, neurology, Johns Hopkins University, Baltimore; Feb. 22, 2008, presentation, American Stroke Association's International Stroke Conference, New Orleans
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