Older people with poor physical function are at higher risk for developing dementia than those with good physical function, reported Li Wang of the Veterans Affairs Puget Sound Health Care System, Seattle, and her associates.
In a study of 2,288 people aged 65 and older, patients with poor standing balance, slowed gait, and poor handgrip had an increased risk of cognitive impairment, dementia, or Alzheimer's disease (AD) developing during 6-year follow-up. The findings suggest physical decline may precede onset of dementia, which may in turn explain why other research has found that physical exercise appears to have a protective effect against dementia, the investigators said.
Ms. Wang and her associates used data from a population-based longitudinal study of aging to examine whether decline in motor function might be linked to progression to dementia. The study subjects were drawn from a random sample of patients enrolled in an HMO who were 65 or older from 1994 to 1996 (Arch. Intern. Med. 2006;166:1115–20).
All subjects had normal cognitive function on a battery of assessments at their initial screening. Attention, concentration, orientation, short-term memory, long-term memory, language ability, visual construction, list-generating fluency, abstraction, and judgment were assessed.
Subjects also underwent four physical performance tests: a 10-foot timed walk, timing of the interval required to rise from a seated position, standing balance, and grip strength. They were reexamined every 2 years to identify incident dementia and AD, the investigators said.
During a 6-year follow-up, 1,422 subjects remained free of dementia, 362 died, 185 withdrew from the study, and 319 developed dementia–221 with AD, 55 with vascular dementia, and 43 with other types of dementia.
The incidence of dementia was 53/1,000 person-years for subjects who had poorer physical function at baseline (below the 25th percentile), compared with 17/1,000 person-years for those with better physical function.
Similarly, among subjects with the highest physical function scores at baseline, the incidence of dementia was 15/1,000 person-years, compared with an incidence of 58/1,000 person-years among those with lower scores.
When the results of each physical function test were considered separately, gait slowing and poor balance developed early, before any signs of cognitive impairment. Poor grip strength developed somewhat later, when cognitive impairment was just beginning to emerge.
“Gait and balance require integration of motor, sensory, and cerebellar activities, whereas grip requires a simpler motor activity. The more 'brain-challenging' tasks of gait and balance could be affected earlier in the course of dementia, whereas a simpler motor task such as grip would likely be preserved until later in the disease course,” Ms. Wang and her associates said.
If their findings are confirmed in future studies, it would indicate that gait slowing and poor balance are earlier markers and poor handgrip a later marker of preclinical dementia, they added.
Until then, “we speculate that physical decline and cognitive decline may be inseparable during the development of dementia,” they said.