Examining the dynamic, bidirectional associations between cognitive and physical functioning in older adults.

The delineation of the interrelationships between cognitive and physical functioning in older adults is critical to determining pathways to disability. By using longitudinal data from 395 initially high-functioning, community-dwelling older women in Baltimore, Maryland, from the Women's Health and Aging Study II (from 1994 to 2006), we simultaneously assessed associations of cognition with later physical functioning and associations of physical functioning with later cognition. The analysis included measures of global cognition and 2 cognitive domains (executive functioning and memory), as well as 2 measures of physical functioning (a Short Physical Performance Battery and a 4-meter test of usual walking speed). We found the strongest bidirectional associations of memory with physical functioning and less evidence of associations of physical functioning with executive functioning and global cognition. For a 1-standard deviation increase in walking speed, subsequent memory increased by 0.08 standard deviations (95% confidence interval: (0.03, 0.13)). For a 1-standard deviation increase in memory, subsequent walking speed increased by 0.07 standard deviations (95% confidence interval: 0.03, 0.10). Associations were similar in magnitude for models using a Short Physical Performance Battery. We did not find evidence that associations between cognitive and physical functioning varied over time. Our results suggest that cognition, and particularly memory, is associated with subsequent physical functioning and vice versa.