A new study of cognitive impairment, the first population-based study of cognitive impairment in the U.S., suggests that the condition may affect a significant proportion of older people. The research, which looked at cognitive difficulties falling short of Alzheimer's disease or dementia among community-dwelling older African Americans in Indianapolis, IN, found that nearly one in four had measurable cognitive problems. In addition, prevalence increased with age, the study finding that 38 percent of people age 85 and older had some degree of cognitive impairment short of dementia. The findings appear to be consistent with the few studies done so far in other countries.
The research is reported in the November 13, 2001, issue of the journal Neurology . Authored by Frederick W. Unverzagt, Ph.D., Hugh Hendrie, MB ChB, and colleagues at Indiana University School of Medicine, with researchers from the Regenstrief Institute for Health Care in Indianapolis and the University of Ibadan in Nigeria, the work was supported by grants from the National Institute on Aging (NIA) and the Alzheimer's Association.
Cognition is the process of thinking, learning, and remembering. Research to understand cognitive impairment that is not dementia is a particularly active area of study. Whether measured as Cognitive Impairment No Dementia (CIND), as in this study, or Mild Cognitive Impairment (MCI), as in a number of other studies, scientists are trying to determine the condition's prevalence in the population and how it may relate to the development of Alzheimer's disease or dementia later on.
"It is increasingly important to learn more about how to measure and characterize this condition," says Neil Buckholtz, Ph.D., chief of the NIA's Dementias of Aging Branch and project officer for the study. "Cognitive impairment is emerging as a major risk factor for Alzheimer's disease and dementia and, in and of itself, may cause functional problems for older people." Ultimately, Buckholtz says, research in this area will help lead to earlier diagnosis and treatment of cognitive and memory problems among older people.
The researchers looked at a group of people from the Indianapolis site of the Indianapolis-Ibadan Dementia Project, an ongoing longitudinal study of aging and dementia among comparable populations in the two cities. The Project, which involves people living in both the community and in institutions, is notable as an important study of African Americans and for its value as a cross-cultural study of dementia in the U.S. and in Nigeria. In February 2001, a report by Hendrie and colleagues from Indiana University and the University of Ibadan on the incidence of dementia found that African Americans in Indianapolis were twice as likely as Africans to develop dementia and Alzheimer's disease.
This particular study of cognitive impairment involved 2,212 people age 65 and older living in the community and 106 people age 65 and older living in nursing homes in the Indianapolis area. A total of 457 participants (351 in the community and 106 in nursing homes) received full clinical assessments and a diagnosis. In a number of cases, the researchers conducted interviews with spouses or close relatives or sources who could describe a participant's symptoms and the progression of symptoms of memory loss, language disturbance, decline in judgment and reasoning, and personality change. After the baseline assessment, the clinically assessed participants were followed for up to 48 months from the start of the study.
In this study, according to Unverzagt, "the prevalence of cognitive impairment was significant, especially with advancing age." Applying the findings from the clinically assessed group to the larger community sample, the researchers estimated that 23.4 percent of the community-dwelling participants and 19.2 percent of the nursing home residents had CIND. The prevalence of cognitive impairment grew significantly with age, with rates increasing by about 10 percent for every 10 years of age after age 65. CIND was almost five times more common in the community than dementia (23.4 percent CIND to 4.8 percent dementia for people 65 and older).
In addition, the scientists found, 26 percent of those characterized with CIND at the start of the study went on to become demented only 18 months later, although 24 percent of participants who were first diagnosed with CIND appeared normal after 18 months. The factors that influence whether CIND will progress to dementia or return to normal have not yet been defined.
Whether the prevalence of cognitive impairment short of dementia in the Indianapolis group is any higher or lower than other population groups is unclear. The new analysis is the first reported in the U.S. and one of only a few worldwide that have examined the prevalence of cognitive impairment short of dementia. In the research so far, findings of prevalence in large epidemiological surveys have ranged from 10.7 percent in Italy to 26.6 percent in Finland. The variation in findings can be explained by differences in study methodology, including diagnostic criteria, although it is difficult to compare findings directly, the researchers note. However, Unverzagt suggests, these studies to date do suggest that mild cognitive impairment may be common.
The Indianapolis data were approached from a second perspective, figuring the proportion of people in different age groups who were cognitively normal instead of impaired. Incorporating information about the prevalence of dementia from earlier studies of the Indianapolis group, the team added together the prevalence of CIND and dementia, and then looked at the proportion remaining, classified as normal. Looked at this way, only 45 percent of people age 84 and older were found to be cognitively normal, compared with 79 percent of people ages 65 through 74.
The NIA leads the Federal effort to support and conduct basic, clinical, and social and behavioral studies on AD. It also supports the Alzheimer's Disease Education and Referral (ADEAR) Center, which provides information to the public, health professionals, and media. ADEAR can be contacted toll free at 1-800-438-4380 weekdays during business hours or by viewing www.nia.nih.gov/alzheimers.
To contact Unverzagt, call Mary Hardin at the Indiana University School of Medicine, at (317) 274-7722.
To contact the Alzheimer's Association, call Ted Bobrow, Acting Director of Media Relations, at (312) 335-5834. The Association may also be reached toll free at 1-800-272-3900 or by visiting its Web site at www.alz.org.