"Declining cognitive function in older adults is a major personal and public health concern," said Bruce Reed, professor of neurology and associate director of the UC Davis Alzheimer's Disease Center.
"But not all people lose cognitive function, and understanding the remarkable variability in cognitive trajectories as people age is of critical importance for prevention, treatment and planning to promote successful cognitive aging and minimize problems associated with cognitive decline."
The study, "Life Experiences and Demographic Influences on Cognitive Function in Older Adults," is published online in Neuropsychology, a journal of the American Psychological Association. It is one of the first comprehensive examinations of the multiple influences of varied demographic factors early in life and their relationship to cognitive aging.
The research was conducted in a group of over 300 diverse men and women who spoke either English or Spanish. They were recruited from senior citizen social, recreational and residential centers, as well as churches and health-care settings. At the time of recruitment, all study participants were 60 or older, and had no major psychiatric illnesses or life threatening medical conditions. Participants were Caucasian, African-American or Hispanic.
The extensive testing included multidisciplinary diagnostic evaluations through the UC Davis Alzheimer's Disease Center in either English or Spanish, which permitted comparisons across a diverse cohort of participants.
Consistent with previous research, the study found that non-Latino Caucasians scored 20 to 25 percent higher on tests of semantic memory (general knowledge) and 13 to 15 percent higher on tests of executive functioning compared to the other ethnic groups. However, ethnic differences in executive functioning disappeared and differences in semantic memory were reduced by 20 to 30 percent when group differences in childhood socioeconomic status, adult literacy and extent of physical activity during adulthood were considered.
"This study is unusual in that it examines how many different life experiences affect cognitive decline in late life," said Dan Mungas, professor of neurology and associate director of the UC Davis Alzheimer's Disease Research Center.
"It shows that variables like ethnicity and years of education that influence cognitive test scores in a single evaluation are not associated with rate of cognitive decline, but that specific life experiences like level of reading attainment and intellectually stimulating activities are predictive of the rate of late-life cognitive decline. This suggests that intellectual stimulation throughout the life span can reduce cognitive decline in old age."
Regardless of ethnicity, advanced age and apolipoprotein-E (APOE genotype) were associated with increased cognitive decline over an average of four years that participants were followed. APOE is the largest known genetic risk factor for late-onset Alzheimer's. Less decline was experienced by persons who reported more engagement in recreational activities in late life and who maintained their levels of activity engagement from middle age to old age. Single-word reading - the ability to decode a word on sight, which often is considered an indication of quality of educational experience - also was associated with less cognitive decline, a finding that was true for both English and Spanish readers, irrespective of their race or ethnicity. These findings suggest that early life experiences affect late-life cognition indirectly, through literacy and late-life recreational pursuits, the authors said.
"These findings are important," explained Paul Brewster, lead author of the study, a doctoral student at the University of Victoria, and a pre-doctoral psychology intern in the UC San Diego Department of Psychiatry, "because it challenges earlier research that suggests associations between race and ethnicity, particularly among Latinos, and an increased risk of late-life cognitive impairment and dementia.
"Our findings suggest that the influences of demographic factors on late-life cognition may be reflective of broader socioeconomic factors, such as educational opportunity and related differences in physical and mental activity across the life span."
The other study authors are Rebecca J. Melrose, UCLA and the VA Greater Los Angeles Health System; Maria Marquine, UC San Diego; Julene K. Johnson and Anna Napoles, UC San Francisco; Anna McKay-Brandt, Nathan Kline Institute for Psychiatric Research, New York; and Sarah Farias, Bruce Reed and Dan Mungas, UC Davis.
The study was supported by grants from the U.S. National Institute on Aging and a grant from the Canadian Institutes for Health. It was developed as part of a conference sponsored by the National Institute on Aging and organized by UC Davis that promotes collaborative science in cognitive aging research.
The UC Davis Alzheimer's Disease Center is one of only 27 research centers designated by the National Institutes of Health's National Institute on Aging. The center's goal is to translate research advances into improved diagnosis and treatment for patients while focusing on the long-term goal of finding a way to prevent or cure Alzheimer's disease. Also funded by the state of California, the center allows researchers to study the effects of the disease on a uniquely diverse population. For more information, visit alzheimer.ucdavis.edu.
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