Findings from this study, funded by the National Institute on Aging, will be presented Tuesday, April 4, at the American Academy of Neurology meeting in San Diego.
The researchers randomly selected 3,957 people from the general population of Olmsted County, Minn., home of Mayo Clinic, for participation in this study. The researchers set out to find how many of those who did not have dementia might have mild cognitive impairment. To date, 1,116 people without dementia in the study have been evaluated.
The findings suggest that 12 percent of 70- to 89-year-olds in Olmsted County, Minn., have mild cognitive impairment. The prevalence of mild cognitive impairment increased with age, affecting 9 percent of those 70 to 79 and nearly 18 percent of those 80 to 89. The prevalence of mild cognitive impairment also varied according to years of education, ranging from 25 percent in those with up to eight years of education, 14 percent in those with nine to 12 years, 9 percent in those with 13 to 16 years, and 8.5 percent in those with greater than 16 years.
The researchers suggest that the increase of mild cognitive impairment with age found in this study parallels the risk elevation with age seen in previous studies of Alzheimer's disease.
"This means that 12 percent to 20 percent of the entire population of those over age 70 may have either mild cognitive impairment or dementia, which is quite significant," says Ronald Petersen, M.D., Ph.D., Mayo Clinic neurologist and study investigator. "These data have major implications for the future of the health care system and the aging of America."
Dr. Petersen adds that the increased risk for mild cognitive impairment with fewer years of education found in this study parallels other studies' findings of a similar rise in risk for Alzheimer's disease as years of education decrease.
"People with more years of education also may experience a loss of cognitive ability, but they can compensate better and thus they don't demonstrate the symptoms of mild cognitive impairment," says Rosebud Roberts, M.B.Ch.B., Mayo Clinic epidemiologist and lead study investigator. "It's as though their education protects them from exhibiting the effects of mild cognitive impairment."
Dr. Petersen explains that mild cognitive impairment is "the transitional stage between normal aging and dementia." This condition may encompass deficiencies in any or all of the following categories:
- Language --words don't come as quickly as they once did
- Visuospatial ability --placement of things in time and space becomes more difficult, such as having trouble getting the proportions right when drawing a box
- Executive function --decision making becomes more challenging
- Memory --recent recall diminishes, such as what one did yesterday
Patients with mild cognitive impairment otherwise function normally in society, indicates Dr. Roberts. In fact, she explains, the symptoms of mild cognitive impairment can be so subtle that they are difficult to detect unless living with the affected person.
The current research findings are preliminary; an additional 800 to 900 people will be evaluated before the study's completion. Mayo Clinic's long-term hope with this research, according to Dr. Roberts, is to identify factors that protect against mild cognitive impairment and help develop treatments for those affected, thus minimizing the likelihood of progression to Alzheimer's disease.