General physical activity is already known to enhance cardiovascular health and help maintain independence and quality of life in older people, but the results of this study - which establish a statistical association, and not a direct cause and effect, between variety of exercise and reduced dementia risk -- suggest that participating in a number of different activities may be as or more important than frequency, duration, and intensity of physical activity with respect to dementia risk, according to the report.
"We don't yet know why this association exists or what causes it. It could well be that maintaining a variety of activities keeps more parts of the brain active, or that this variety reflects better engagement in both physical and social activities. Confirmation of this association in future studies may provide an additional impetus for people to remain or become engaged in several physical and other leisure activities later in life," says Constantine G. Lyketsos, M.D., professor of psychiatry and behavioral sciences at Johns Hopkins and senior author on the report.
The study included 3,375 men and women age 65 years or older who participated in the Cardiovascular Health Cognition Study from 1992 to 2000 and who did not have dementia at the onset of the study. Each study volunteer was asked to fill out a questionnaire about the frequency and duration of the 15 most common types of physical activity in older adults, including walking, household chores, mowing, raking, gardening, hiking, jogging, biking, exercise cycling, dancing, aerobics, bowling, golfing, general exercise and swimming. The researchers then created an activity index, calculated as the number of different activities each subject participated in over the previous two weeks. Other measurements, including APOE gentotype, age, gender, education level, ethnicity, smoking, alcohol use, and other physical and mental health-related history, were also considered in the study.
The researchers found 480 new cases of dementia over an average of 5.4 years of follow-up. Among these, dementia occurred less frequently in those participating in more activities relative to those who participated in fewer activities (one or no activity had 130 cases, two activities had 152 cases, three activities had 113 cases, four or more activities had 84 cases). The association held true for all types of dementia, including Alzheimer's disease and vascular dementia. The association did not hold true for those who have the APOE-4 genotype.
"These findings, taken together with recent findings from our colleagues at the University of Chicago studying physical activity and plaque buildup in the brains of mice with Alzheimer's (published this year in the journal Cell) provide a good picture from basic and clinical science of how activity and exercise work to reduce the risk of dementia," says Lyketsos.
According to the Alzheimer's Association, dementia is a group of diseases that all gradually destroy brain cells and lead to progressive decline in mental function. An estimated 4.5 million Americans have Alzheimer's disease, the most common form of dementia. The number of American's with Alzheimer's disease has more than doubled since 1980 and is projected to reach 11.3 to 16 million by the year 2050.
Other authors of the report are Laura Jean Podewils, Eliseo Gualler, Linda Fried and Michelle Carson of Johns Hopkins, and Lewis H. Kuller and Oscar L. Lopez of the University of Pittsburg. The research was funded by the National Heart, Lung and Blood Institute and the National Institute on Aging.
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