The population of individuals age 90 and better is growing, but is not often included in research studies. Research has identified an association between decreased physical performance and cognitive decline in younger older adult populations, but the relationship between physical performance and dementia has not been examined in the oldest old. A study in the Journal of the American Medical Association Neurology examined the relationship between dementia and four physical performance measures in a sample of 629 participants age 90 or better.
The 90-and-up population is distinctive for reasons other than longevity. Individuals who reach 90 years of age, most of whom are women, are generally of higher educational status and have better than average health throughout the life course. This population also has the highest rate of dementia diagnosis and physical disability, however, making those 90 and better a useful population in which to study the relationship between physical and cognitive well-being.
The individuals in the study were participants from the 90+ Study, a longitudinal study that began in the 1980s in a retirement community in Southern California. The study included neurological evaluations, medical history assessments, and physical performance measures. The physical performance measures included a timed four-meter walk, five timed chair stands (in which participants are asked to fold their arms across their chests and stand from a sitting position), tests of balance, and grip strength.
In their analysis of the data, the researchers found that poor physical performance in each of the measures was associated with an increased likelihood of dementia. The strongest association was with gait speed, as participants who were unable to walk were about 30 times more likely to have a diagnosis of dementia than the fastest walkers. Some have suggested that the association between walking and dementia, which has been identified in many studies, is due to the fact that walking requires the coordination of multiple cognitive abilities, which makes gait speed a particularly useful marker for cognitive risk.
There are several possible explanations for the relationship between dementia and physical performance. There may be an underlying neurological explanation that contributes to both, or, alternately, declines in physical performance may lead to physical inactivity, which is a known risk factor for cognitive decline. The fact that physical and cognitive performance are associated with one another even in the oldest old may contribute to our understandings of the causes of dementia.
Bullain SS, Corrada MM, Shah BA, et al. Poor physical performance and dementia in the oldest old: the 90+ study. JAMA Neurology (2013); 70(1): 107–112.