Landmark study links cognitive ability of youth with Alzheimer's disease risk later in life
Women who scored poorly on measures of cognitive ability as young adults were found to be at higher risk for Alzheimer's disease and poor cognitive function in late life, according to a new report by researchers at the University of Kentucky. The groundbreaking study of nearly 100 nuns found that the complexity of the sisters' writings as young women had a great deal to do with how they fared cognitively later in life. Of the nuns who died, 90 percent of those with Alzheimer's disease confirmed at autopsy had low linguistic ability in early life, compared with only 13 percent in those without evidence of the disease.
The report appears in the February 21 Journal of the American Medical Association. The Nun Study was funded by the National Institute on Aging (NIA).
David A. Snowdon, Ph.D., of the University of Kentucky's Sanders-Brown Center on Aging and lead author of the report, says the findings show that written linguistic performance, the study's measure of cognitive ability in early life, "is a potent marker for cognitive problems, Alzheimer's disease, and brain lesions in late life."
Why this happens is not altogether clear. Snowdon and his colleagues approached the study with the idea that full development of the brain and cognitive abilities early in life, through education or other stimulation, may provide a "neurocognitive reserve" that protects people from Alzheimer's disease and cognitive problems later. Educational differences, however, did not explain the relationship between low linguistic ability in early life and poor cognitive function later on. Combining that with the study's findings on the nature of lesions in the brain, the scientists developed an alternate theory -- that low linguistic ability in early life could be a subtle symptom of very early changes in the brain that ultimately lead to Alzheimer's disease.
NIA scientists note that the Nun Study is one of the first long-term studies in a well-controlled population to suggest that the process of Alzheimer's disease may begin earlier in life than previously thought. Richard M. Suzman, Ph.D., chief of the NIA's Demography and Population Epidemiology Branch and program officer for the Nun Study, says the effort "represents an exciting new area of research into how factors in early life, such as cognitive ability, birthweight, and socioeconomic status, relate to diseases and functioning later on. I expect that this study will ignite interest in similar longitudinal research, following people from early life into old age. Ultimately, these types of studies will allow us to better predict who is at risk for a variety of age-related diseases."
Neil Buckholtz, Ph.D., acting associate director for the Neuroscience and Neuropsychology of Aging Program at the NIA, says that the Nun Study's link between factors early in life and disease later on is important in the search to understand the progression and manifestation of Alzheimer's disease.
But linguistic ability in early life, while possibly a marker for Alzheimer's disease, needs to be examined further, according to Buckholtz. Other factors could explain the link between early cognitive differences and disease in old age. "It may be that inherited differences in cognitive ability, factors that may have nothing to do with the disease per se, may affect the way the Alzheimer's process unfolds in an individual," he says. "Those with higher linguistic ability early in life may be more resistant to later influences which lead to the disease while those with lower ability as young adults may be more at risk."
Additional research supported by the Institute and from the continuing Nun Study, including an examination of genetic factors, may help scientists determine why in this study the early linguistic performance proved so predictive of future disease.
Participants in the Nun Study are members of the School Sisters of Notre Dame religious congregation. For this aspect of the research, the study concentrated on those who joined the Milwaukee convent from 1931 through 1939 and who had written autobiographies at an average age of 22.
The autobiographies were examined for linguistic ability as a test of cognitive function in early life. One component of linguistic ability, "idea density," defined as the average number of ideas for each 10 written words, is associated with educational level, vocabulary, and general knowledge, while a second measure, "grammatical complexity," is linked with working memory, performance on timed tests, and writing skills. Approximately 58 years after they had written their autobiographies, the women took part in tests of cognitive abilities. For the 25 nuns who died, brain tissue was examined at autopsy.
The study found that low idea density shown in the writings of the young women was strongly linked with low cognitive test scores and the presence of Alzheimer's disease in late life. For example, the nuns with low idea density scores were 30 times more likely to do poorly on a standard measure of cognitive function, the Mini-Mental State Exam, than those with more complex writings. An even more dramatic difference was observed when cognitive ability and characteristics of brain tissue were compared in the nuns who died. Neurofibrillary tangles of Alzheimer's disease appeared in about 90 percent of those nuns who had low linguistic ability in early life.
The NIA, part of the National Institutes of Health, leads the Federal effort supporting and conducting Alzheimer's disease research, including studies of the basic, clinical, demographic, and epidemiological aspects of Alzheimer's disease and other dementias of aging. The Nun Study is being conducted in part by the University of Kentucky Alzheimer's Disease Research Center, one of 27 Alzheimer's Disease Centers (ADCs) supported by NIA at major medical institutions across the U.S. The ADCs work to improve current care and diagnostic techniques for Alzheimer's patients and conduct research aimed at preventing and treating the disease. For general information on the centers, contact the NIA's Alzheimer's Disease Education and Referral Center (ADEAR) at 1-800-438-4380.