Walking Ability Linked to Dementia Risk in the Very Old
People older than age 90 years who are unable to walk are about 30 times more likely to have dementia than those of about the same age who can walk the fastest, according to a new cross-sectional study.
Researchers found that the relationship between declines in walking speed, grip strength, and balance and the odds of dementia were dose dependent: The slower the walking or the worse the grip strength, the higher the likelihood of having dementia.
The results suggest that poor physical performance is a risk factor for dementia, the authors conclude.
"This study is the first step in examining the relationship between physical performance and dementia in this age group known as the 'oldest old'," lead author Szofia S. Bullain, MD, clinical instructor and postdoctoral fellow in geriatric neurology, Department of Neurology, University of California, Irvine told Medscape Medical News.
Because this group is the fastest-growing segment of the population and has the highest rate of dementia, it's important to identify modifiable risk factors, she said.
The study was published online October 22 in the Archives of Neurology.
90+ Study
The analysis included 629 participants in the 90+ Study, a population-based longitudinal study of aging and dementia. The mean age of participants was 94 years; most were white, female (72.5%), and educated survivors from the Leisure World Cohort Study, an epidemiologic study of a retirement community in Orange County, California, that was established in the early 1980s.
Researchers evaluated participants on 4 tests of physical performance: the 4-meter walk, 5 timed chair stands, 10-second standing balance, and grip strength. For each participant, they developed a score (from 0 to 4).
In addition, all participants underwent detailed neurologic evaluations that included the Mini-Mental State Examination, the Washington University Clinical Dementia Rating Scale, and the Functional Activities Questionnaire. Among the 629 participants, dementia was diagnosed in 162 (25.8%).
The study found a strong relationship between poor physical performance and dementia, with the most notable effect being in the 4-meter walk test. Those who were unable to walk (score 0) were almost 30 times more likely to have dementia than participants with the fastest walking time (score 4).
Even minimal slowing in walking speed (≤1.5 seconds, from score 4 to score 3) resulted in a 4 times greater odds of dementia.
Dementia Risk for No Walking (Score 0) or Minimal Slowing (Score 3) vs Fastest Walking (Score 4)
| Comparison | Odds Ratio (95% Confidence Interval) | P Value |
| Score 0 vs score 4 | 28.3 (11.5 - 70.1) | < .001 |
| Score 3 vs score 4 | 4.0 (1.7 - 9.7) | .002 |
Complex Process
Walking or gait is a complex process requiring coordination of several neurologic systems, including motor, sensory, and cerebellar activities. "That's why it takes us so long to even acquire that ability; it takes most babies a year to learn to walk," said Dr. Bullain.
The next highest odds of dementia were associated with poor performance in the 5 chair stands, which required participants to stand from a sitting position with their arms folded across their chest (odds ratio [OR], 15.9; P < .001), followed by grip strength in the dominant hand (OR, 9.8; P < .001) and standing balance in various positions (OR, 9.5; P < .001).
These last 2 measures "were very, very similar," she said, and really can't be distinguished in terms of strength of association, said Dr. Bullain.
The dose-dependent association was similar for men and women for most tasks, except for the magnitude of the association between the "unable to do" (score 0) and dementia on the 4-meter walk tests. Here, the odds ratio was 138.4 for men and 27.1 for women. The increased odds ratio for men is probably due to the small sample size, said Dr. Bullain. There were 173 men (27.5%).
Adjusting for a history of cerebrovascular and cardiovascular disease didn't significantly change the odds of dementia in any of the performance measures.
"Large vessel strokes are often associated with poor walking or difficulty walking, but this adjustment for history of strokes or even TIAs [transient ischemic attacks] or vascular brain disease did not change the results significantly," commented Dr. Bullain. "This is a little counterintuitive, but we think it's due to a low prevalence of large-vessel strokes in our cohort; if you have large-vessel strokes in the brain, you're not that likely to live to this age."
Large-vessel strokes accounted for 8.6% of all cerebrovascular events in the study.
The main analysis, which included only participants with data on all 4 measures, might have missed people who are out of shape or have physical or cognitive limitations, and therefore could have lessened the strength of the association. But an analysis of the 4 measures separately, which included those with only partial data, showed only minimal changes in the results, said Dr. Bullain.
Parallel Fashion
The cross-sectional design of the study doesn't allow for an evaluation of the temporal relationship between poor physical performance and dementia. "So we can't tell which came first, whether it was the poor physical performance or the dementia," said Dr. Bullain.
It could be that poor physical performance somehow leads to impaired cognition, and could be a risk factor for dementia, possibly a modifiable one. It's also possible that poor cognition leads to poor physical performance; if someone doesn't understand a command, for example, to stand up 5 times, it will probably take that person longer to complete the task.
"A third explanation is that both poor physical performance and dementia are different manifestations of the same neurodegenerative process, in which case they occur almost independently, sort of in a parallel fashion," said Dr. Bullain.
She and her research colleagues are wrapping up a longitudinal analysis that should address these issues and help determine whether poor physical performance is indeed a risk factor for dementia, said Dr. Bullain.
"If slow walking is a modifiable risk factor, we could provide exercise training or maybe strength training so people would be able to walk faster or be able to stand up 5 times from the chair more quickly, and maybe that will reduce their risk of developing dementia — that's our long-term goal."
Important Role for Physical Performance
Asked to comment, Arthur F. Kramer, PhD, professor, Department of Psychology, University of Illinois, Champaign, whose research interests include cognitive and brain plasticity, aging, and cognitive neuroscience, said the study is "rather unique" in that it examined the relationship between dementia and physical performance in those 90 years of age and older, a subset of the population that is understudied but rapidly growing.
"The relatively strong relationship between performance, and in particular walking speed, and dementia is interesting and certainly merits additional study," Dr. Kramer told Medscape Medical News. "However, at present the explanation of this relationship is ambiguous given the correlational nature of the study."
For his part, Kirk I. Erickson, PhD, assistant professor in the Department of Psychology, Centers for Neuroscience and Neural Basis of Cognition, University of Pittsburgh, Pennsylvania, said the study "aligns nicely" with other research in younger participants showing that physical activity and fitness levels are important factors in risk for dementia.
"It is clear from this study and others that physical performance in late life plays an incredibly important role in our cognitive health," said Dr. Erickson. "Although more research is needed into the causal mechanisms and pathways by which this works, it is clear that physical performance in late life is critical for retaining a healthy brain."
The study was supported by grants from the National Institute on Aging. Dr. Bullain has disclosed no relevant financial relationships.
Arch Neurol. Published online October 22, 2012. Abstract
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Cite this article: Walking Ability Linked to Dementia Risk in the Very Old. Medscape. Oct 29, 2012.
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