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Life space and risk of Alzheimer disease, mild cognitive impairment, and cognitive decline in old age.

OBJECTIVE
To test the hypothesis that a constricted life space, the extent of movement through the environment covered during daily functioning, is associated with increased risk of incident Alzheimer disease (AD), increased risk of mild cognitive impairment (MCI), and more rapid cognitive decline in older adults.


DESIGN
Two prospective cohort studies.


SETTING
Retirement communities, community-based organizations, churches, and senior subsidized housing facilities across the Chicago metropolitan area.


PARTICIPANTS
A total of 1,294 community-dwelling elders without baseline clinical dementia.


MAIN OUTCOME MEASURES
Detailed annual clinical evaluation to diagnose incident AD and MCI, and document change in cognitive function.


RESULTS
During a mean (SD) follow-up of 4.4 (1.7) years, 180 persons developed AD. In a proportional hazards model controlling for age, sex, race, and education, a more constricted life space was associated with an increased risk of AD (hazard ratio = 1.21, confidence interval: 1.08-1.36). A person with a life space constricted to their home was almost twice as likely to develop AD than a person with the largest life space (out of town). The association did not vary along demographic lines and persisted after the addition of terms for performance-based physical function, disability, depressive symptoms, social network size, vascular disease burden, and vascular risk factors. The association remained consistent after excluding persons with MCI at baseline and who developed AD in the first 2 years of observation. A constricted life space was also associated with an increased risk of MCI (hazard ratio = 1.17, confidence interval: 1.06-1.28), and a more rapid rate of global cognitive decline (estimate: -0.012, standard error: 0.003, t[5033] = -3.58, p <0.001).


CONCLUSIONS
A constricted life space is associated with increased risk of AD, MCI, and cognitive decline among older persons.