CHICAGO — Men have more mild cognitive impairment than women do, yet there is no gender difference in the prevalence of dementia, according to the results of one of the first studies to measure mild cognitive impairment prospectively in a population-based setting.
The findings, reported by Dr. Rosebud O. Roberts at the annual meeting of the American Academy of Neurology, suggest that dementia progresses either faster in women or slower in men.
For the ongoing study, called the Mayo Clinic Study of Aging, mild cognitive impairment (MCI) was evaluated in a population sample from Olmstead County, Minn. The 70- to 79-year-old group included 490 women and 596 men. The 80- to 89-year-old group included 512 women and 452 men. For both age groups, there were 1,002 women and 1,048 men.
A nurse, physician, or neuropsychologist evaluated each individual using face-to-face measures. Subjects were evaluated in four domains—memory, executive function, language, and visual/spatial skills. MCI was defined as impairment in one or more domains or an overall mild decline across cognitive abilities that is greater than would be expected for an individual's age or education but is insufficient to interfere with social and occupational functioning.
Based on these evaluations, 74% of the group had normal cognition, 16% had MCI, and 10% had dementia. Of the nearly 2,000 study participants without dementia, 51% were male, 47% had less than 12 years of education, 52% were 80–89 years old, and 61% were married.
Subjects were studied prospectively beginning in October 2004 and follow-ups will continue through 2010. This differs from most other studies of MCI, which had the limitations of applying MCI criteria to previously collected data or were conducted in study samples, such as those attending memory clinics, who might not be representative of the general population.
In men, the prevalence of mild cognitive impairment steadily increased from about 10% at age 70 and suddenly spiked after age 85 to affect 40%. In women, the rate rose more slowly and the prevalence was far lower, peaking at less than 20% at age 85.
Even after the data were corrected for age plus education, marital status, and disease burden, women had less cognitive impairment but comparable rates of dementia, compared with men, Dr. Roberts said.
“We found the overall prevalence of mild cognitive impairment is quite high—over 16%,” said Dr. Roberts. “But perhaps the more surprising finding is the higher prevalence of MCI in men with the comparable prevalence of dementia for men and women.” Several possible explanations for this disparity include a prevalence of risk factors in middle age vs. later life, the progression rate from MCI to dementia, and death among persons with MCI.
Dr. Roberts said that she and her coinvestigators are in the process of adding another 1,000 participants to continue the follow-up study. The study was supported by the National Institutes of Health and the Robert H. and Clarice Smith and Abigail Van Buren Alzheimer's Disease Research Program.