Both physical performance and cognitive (thinking, learning and memory) ability tend to decline with age, often as a result of age-related diseases, according to background information in the article. Some studies have shown a link between physical and cognitive decline but few have examined how physical performance is linked to the development of dementia or the intermediate stage known as cognitive impairment. "Identifying signs associated with progression to dementia would assist in predicting the development of dementia and has important implications for interventions to slow the progression to these devastating illnesses," the authors write.
Li Wang, M.S., VA Puget Sound Health Care System, University of Washington, Seattle, and colleagues studied 2,288 individuals age 65 years and older who did not have dementia at the beginning of the study. Between 1994 and 1996, participants underwent initial testing to determine their cognitive abilities, which were scored on a scale from zero to 100. They also performed four established tests of physical function: a timed, 10-foot walk; a chair-stand test, timing participants as they stood from a seated position five times; a standing balance assessment; and a measurement of grip strength in the dominant hand. Each individual was given a score of zero to four on each test, with four representing the highest level of functioning; those scores were added to obtain a total physical performance score of up to 16. Participants were then assessed every other year through October 2003 for the development of dementia.
At the beginning of the study, those with lower physical performance scores also had lower cognitive scores. During the six years of follow-up, 319 participants developed dementia, including 221 with Alzheimer's disease. Those with physical performance scores higher than 10 were much less likely to develop dementia than those with scores of 10 or lower. Each one-point decrease on the physical performance scale was associated with an increased risk of dementia, Alzheimer's disease and a more rapid decline in cognitive performance scores. This association remained when researchers accounted for other factors, including age, gender, education, other mental and physical illnesses, cognitive function at the beginning of the study and a family history of or genetic predisposition to Alzheimer's disease.
Individual physical abilities were linked to different stages in the development of dementia. "We observed that among participants without apparent cognitive impairment, those with gait slowing and poor balance were more likely to develop dementia, and among participants with possible mild cognitive impairment, those with poor handgrip were more likely to develop dementia," the authors write. "These findings suggest that gait slowing and poor balance might relate to dementia and may occur during an earlier stage before cognitive impairment is apparent, and that poor handgrip might relate to dementia during a later stage when cognitive impairment has occurred."
"If confirmed, this study might also help explain the association of physical exercise with a reduced risk of dementia, suggesting that exercise, by improving and maintaining physical function, might benefit cognitive function through a connection between the two," they conclude.
(Arch Intern Med. 2006; 166: 1115-1120. Available pre-embargo to media at www.jamamedia.org.)
Editor's Note: This study was supported by a grant from the National Institute on Aging.
Journal
Archives of Internal Medicine