MAINTAINING mobility into old age is important for remaining independent at home and being able to participate in social and leisure activities in the community. Poor mobility increases the risk of fallsand there has been growing interest in whether its presence may suggest an increased risk of dementia.
walking and dementia
Dementia is a leading cause of disability and death in older Australians. When a diagnosis of dementia is made, there has already been a substantial accumulation of pathology in the brain. It is therefore important to quickly identify those at risk in order to address modifiable risk factors for the prevention of dementia and to start new treatments as soon as they become available.
It is well recognized that changes in gait occur in the later stages of dementiacontribute to loss of autonomy and increased risk of falls. However, despite mounting evidence, it is less well known that walking speed may slow many years before a diagnosis of dementia. Otherwise, the combination of slow gait and a subjective cognitive problem increases the risk of dementia to a greater extent than slow gait alone. However, there is a range of cognitive functions, including memory, language, processing speed and executive function, and it is not yet clear which of these functions are relevant to dementia risk when found with a slowing down of walking.
In our new studyusing data from ASPREE (ASPirin in Reducing Events in the Elderly) Clinical Trial, we explored the utility of different cognitive functions to assess the risk of future dementia when combined with decreased walking speed. We hypothesized that the risk would be higher in people with walking decline plus memory decline, as this combination of measures would reflect the presence of a wide range of brain pathologies.
Information and data from 16,855 older adults from Australia and the United States enrolled in the ASPREE study contributed to the analysis. ASPREE was a large clinical trial testing the effectiveness of low-dose aspirin for the primary prevention of dementia and persistent physical disability, and for prolonging independent life. Inclusion criteria were age 70 or older (or 65 or older for US participants from minority groups), without cardiovascular disease, dementia, or significant physical disability. The cases of dementia were confirmed against criteria validated by a group of experts. Walking speed was measured every 2 years over 3 meters at the usual pace, with cognitive measures (measurement of global cognitive function, delayed memory, processing speed and verbal fluency) carried out in alternate years.
Four groups were screened for their future risk of dementia:
- no decline in cognition or gait (reference group);
- gait decline only;
- cognitive decline only, and
- decline in walking and cognition (double decline).
What did we find?
One hundred seventy-eight participants developed dementia during the study period.
The in-person visit schedule was completed by 15,309 participants (median in-person follow-up, 4.5 years) and 1,546 had incomplete follow-up (median in-person follow-up, 2.5 years). Participants with declines in both walking and cognitive function had an increased risk of dementia compared to non-decliners. Dementia risk was highest in participants with combined gait and memory decline, and intermediate in those with either gait decline or cognitive decline alone. Using measurements repeated at multiple points in time (i.e. tracking decline) was a better predictor of risk than measurements taken at a single point in time.
What do these findings mean?
The results of this secondary analysis of ASPREE data underscore the importance of examining walking speed when screening for future dementia risk in older adults, and that the combination of slowed walking and poor memory may be the most predictive combination.
The combination with memory as the best cognitive measure is interesting. The DSM IV criteria for a diagnosis of dementia applied in this study required alteration in a non-memory domain in addition to memory alteration. Previous studies have found slow walking speed is more strongly associated with these non-memory domains such as executive function and processing speed. Slow walking and memory decline may each capture the effects of different brain pathologies.
We know that the majority of people with dementia can have a mixture of pathologies in their brain including harmful amyloid and tau proteins (strongly linked to memory decline) as well as brain damage due to undetected vascular disease (strongly linked to walking decline). Therefore, the combination of walking and memory decline may be best for capturing the risk of these important pathologies affecting a wide range of brain networks.
What should be done in the clinic?
Our results suggest that serial measurements of a simple test of memory and walking speed may be more useful in clinical screening for future risk of dementia in an otherwise healthy older person.
Usually, only a brief cognitive test is used clinically to screen for dementia risk, and gait is often overlooked. Walking speed is quick to measure and only requires a measured distance and a stopwatch, so appealing for general practice. The measurement of walking speed has long been recommended as an indicator of the general state of health of an elderly person.
Gait speeds less than 0.8 to 1.0 m/s are predictive of adverse outcomes such as falls, disability, hospitalization, and mortality (here and here). Therefore, slow walking speed or walking slowdown of more than 0.05 m/s per year should trigger cognition screening, followed by more comprehensive assessment if needed. Those considered at risk may benefit from exercise, healthy diet, social and intellectual engagement, good blood pressure control, diabetes, and other risk factors that can be modified to prevent dementia.
The ASPREE study was conducted out of Monash University’s School of Public Health and Preventive Medicine.
Dr. Taya Collyer is a biostatistics researcher at Monash University.
Associate Professor Michele Callisaya is a physical therapist at the National Center for Health Aging, Monash University and Peninsula Health. She is also a senior researcher at the Menzies Institute for Medical Research at the University of Tasmania.
Statements or opinions expressed in this article reflect the views of the authors and do not necessarily represent the official policy of WADA, the MJA Where Preview+ unless otherwise stated.
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