The study, published in Neuroepidemiology, also found Alzheimer’s disease accounted for almost 70 percent of all dementia, while vascular dementia -- often caused by stroke -- accounted for 17.4 percent. With increasing age, Alzheimer’s disease accounted for progressively more of the dementia cases, so that in the 90-plus age group, it comprised 79.5 percent of dementia cases.
"These conditions affect millions of older Americans and touch nearly every family in some way, and the situation is only going to get worse as the population ages," lead study author Brenda Plassman, of Duke University, in Durham, N.C., said in a statement.
The researchers found the more years of education, the lower the risk of dementia but they found no significant difference in risk between males and females.
The study used data from 856 men and women who participated in the 2002 Aging, Demographics and Memory Study at the University of Michigan Institute for Social Research and Duke University Medical Center.