Mosley said he believes Alzheimer's disease likely isn't caused by a single factor, but rather by a complex process involving multiple factors interacting and accumulating over decades.

"Understanding the risk factors involved in this complex process may lead to new targets for treatment," he said. "It could also allow us to intervene at an earlier point with people who are at high risk for dementia, a time when preventive treatments may be most effective."

Recent research has found African Americans may have a twofold or greater risk for Alzheimer's compared to whites. With one of the largest and most extensively evaluated African-American study subgroups, the study will help illuminate the role of ethnic differences in relative risk for dementia.

Previous findings from the long-term study have indicated the importance of vascular risk factors in predicting decline in cognitive functions such as memory and processing speed. Using brain imaging, researchers have also shown brain changes, such as atrophy and silent strokes, are surprisingly common, even in middle-age adults. They have also found that these brain abnormalities begin to affect cognitive functions as early as middle age.

Source: University of North Carolina