The dynamic relationship between physical function and cognition in longitudinal aging cohorts

Abstract

On average, older people remember less and walk more slowly than do younger persons. Some researchers argue that this is due in part to a common biologic process underlying age-related declines in both physical and cognitive functioning. Only recently have longitudinal data become available for analyzing this claim. We conducted a systematic review of English-language research published between 2000 and 2011 to evaluate the relations between rates of change in physical and cognitive functioning in older cohorts. Physical functioning was assessed using objective measures: walking speed, grip strength, chair rise time, flamingo stand time, and summary measures of physical functioning. Cognition was measured using mental state examinations, fluid cognition, and diagnosis of impairment. Results depended on measurement type: Change in grip strength was more strongly correlated with mental state, while change in walking speed was more strongly correlated with change in fluid cognition. Examining physical and cognitive functioning can help clinicians and researchers to better identify individuals and groups that are aging differently and at different rates. In future research, investigators should consider the importance of identifying different patterns and rates of decline, examine relations between more diverse types of measures, and analyze the order in which age-related declines occur.

Keywords: aging; cognition; correlated change; longitudinal analysis; meta-analysis; physical functioning; systematic review.

Figure 1.

Strategy used to select recently published articles (2000–2011) for a review of the relations between rates of change in physical functioning and cognitive functioning in community-dwelling population samples aged ≥40 years.

Figure 2.

Average standardized regression coefficients (β) obtained when baseline physical function was regressed on cognition at baseline using A) fluid cognition and B) mental state examinations among persons aged ≥40 years, 2000–2011. Data from the study by Kuh et al. (48) were separated by sex (M, men; W, women). Individual studies are represented by squares; subtotals provide within-group variance-weighted averages and are represented by diamonds. Bars, 95% confidence interval (CI).

Figure 3.

Average standardized regression coefficients (β) for the association between change in cognition and baseline physical functioning derived using A) fluid cognition and B) mental state examinations among persons aged ≥40 years, 2000–2011. Data from the study by Auyeung et al. (32) were separated by sex (M, men; W, women). Individual studies are represented by squares; subtotals provide within-group variance-weighted averages and are represented by diamonds. Bars, 95% confidence interval (CI).

Figure 4.

Average standardized regression coefficients (β) for the association between change in physical function and baseline cognition derived using A) fluid cognition and B) mental state examinations among persons aged ≥40 years, 2000–2011. Individual studies are represented by squares; subtotals provide within-group variance-weighted averages and are represented by diamonds. Bars, 95% confidence interval (CI).

Figure 5.

Hazard ratios for development of physical and cognitive impairment over time, estimated using baseline indicators of functioning, among persons aged ≥40 years, 2000–2011. A) Impact of physical functioning at baseline on the risk of cognitive impairment; B) impact of baseline cognition on the risk of physical impairment. Individual studies are represented by squares; the subtotal provides a within-group variance-weighted average and is represented by a diamond. Bars, 95% confidence interval (CI).

Figure 6.

Average standardized regression coefficients (β) for change in fluid cognition derived using change in physical function among persons aged ≥40 years, 2000–2011. Individual studies are represented by squares; subtotals provide within-group variance-weighted averages and are represented by diamonds. Bars, 95% confidence interval (CI).