Study author Dr. Rosebud Roberts of the Mayo Clinic in Rochester, Minn., said the study subjects were ages 70 to 89 and they were interviewed, examined and given cognitive tests. Overall, 15 percent of the group had mild cognitive impairment.

Mild cognitive impairment can also be described as impairment in memory or other thinking skills beyond what's expected for a person's age and education, Roberts said.

"This is one of the first studies to determine the prevalence of mild cognitive impairment among men and women who have been randomly selected from a community to participate in the study," Roberts said the statement.

"These findings are in contrast to studies which have found more women than men -- or an equal proportion -- have dementia, and suggest there's a delayed progression to dementia in men, or alternately, women may develop dementia at a faster rate than men."

The study is being presented at the American Academy of Neurology 60th anniversary annual meeting in Chicago.