Cognitive function is associated with the development of mobility impairments in community-dwelling elders

Abstract

Objective: To examine the association of cognitive function with the risk of incident mobility impairments and the rate of declining mobility in older adults.

Design: Prospective, observational cohort study.

Setting: Retirement communities across metropolitan Chicago.

Participants: A total of 1,154 ambulatory elders from two longitudinal studies without baseline clinical dementia or history of stroke or Parkinson disease.

Measurements: All participants underwent baseline cognitive testing and annual mobility examinations. Mobility impairments were based on annual timed walking performance. A composite mobility measure, which summarized gait and balance measures, was used to examine the annual rate of mobility change.

Results: During follow-up of 4.5 years, 423 of 836 (50.6%) participants developed impaired mobility. In a proportional hazards model controlled for age, sex, education, and race, each 1-unit higher level of baseline global cognition was associated with a reduction to about half in the risk of mobility impairments (hazard ratio = 0.51, 95% confidence interval: 0.40-0.66) and was similar to a participant being about 13 years younger at baseline. These results did not vary by sex or race and were unchanged in analyses controlling for body mass index, physical activity, vascular diseases, and risk factors. The level of cognition in five different cognitive abilities was also related to incident mobility impairment. Cognition showed similar associations with incident loss of the ability to ambulate. Linear mixed-effects models showed that global cognition at baseline was associated with the rate of declining mobility.

Conclusions: Among ambulatory elders, cognition is associated with incident mobility impairment and mobility decline.

Figure 1. Participants Included in These Analyses

The total number of participants who were enrolled and had completed baseline exam at the time of these analyses in the Memory and Aging Project (MAP) and Minority Aging Research Study (MARS) is shown. Also shown are the numbers of those participants who were excluded from these analyses because they did not meet the inclusion criteria or were missing the requisite data.

Figure 2

A scatterplot of the person-specific annual rate of change of both mobility and global cognition during the course of the study for a 25% random sample of the participants included in these analyses. To portray the association between the rate of change in mobility and global cognition, we used a locally weighted regression smooth function that is based on weighted locally linear fits, thereby reducing the influence of outliers on the regression line.