In a study published in the American Journal of Geriatric Psychiatry, now posted online, researchers found that seniors who had a constricted life space were almost twice as likely to develop Alzheimer's disease as seniors whose life space extended well beyond the home.
"Life space may represent a new way to identify, out of a group of older persons displaying no memory or thinking problems, who is likely to go on to develop Alzheimer's disease," said Bryan James, PhD, an epidemiologist in the Rush Alzheimer's Disease Centre and the study's lead investigator.
Participants in the study included 1294 older adults living in the community taking part in two longitudinal studies: the Rush Memory and Aging Project, a study of chronic conditions of aging involving older persons from retirement communities and subsidised housing in Chicago, and the Minority Aging Research Study, which examines risk factors for cognitive decline in older African Americans.
Study participants were followed for an average of four years and up to eight years, receiving annual clinical assessments that included detailed tests of cognitive function. Their life space was assessed through interviews in which they reported whether their lives in the previous week extended beyond their town, outside their neighbourhood, as far as their home's parking lot or yard, or just to their porch or patio, or whether their lives remained confined to their bedroom or home.
At the outset of the investigation, none of the participants showed signs of clinical dementia. Over up to eight years of follow-up, 180 developed Alzheimer's disease. Those who did tended to have more constricted life spaces. Specifically, those with a life space restricted to their immediate home environment at the start of the study were almost twice as likely to develop Alzheimer's disease as those who traveled out of town.
Confinement to the home was also associated with an increased risk of mild cognitive impairment, often a precursor of Alzheimer's, and a more rapid rate of cognitive decline, the hallmark of Alzheimer's disease.
The association with Alzheimer's persisted even when the researchers controlled for the influence of several confounding variables - factors other than life space that might explain the link with cognition - including health problems known to be predictive of Alzheimer's such as cardiovascular disease, disability and depression. The association also did not appear to be driven by diagnostic misclassification or the inclusion of participants with pre-clinical dementia. The same results were observed after removing from the analysis persons with mild cognitive impairment at the beginning of the follow-up period or persons who developed Alzheimer's in the first two years of follow-up.
"The reasons why a constricted life space is associated with an increased risk of Alzheimer's disease is not clear," James said. "Underlying pathology may explain the result. Certain disease processes in the brain may affect how far we move through the world years before they affect our memory and thinking. Alternatively, perhaps life space is an indicator of how much we are actively engaging and challenging our cognitive abilities. But at this point, we don't have the answer."
The study was funded by grants from the Illinois Department of Public Health, the National Institute on Aging and the Robert C. Borwell Endowment Fund.
Source: Rush University Medical Centre
