Alzheimer's, Dementia & Mental Health
Older People Likely to See Alzheimer’s Risk Increase
as Muscle Strength Weakens
Greater muscle strength associated with decreased
risk of developing Alzheimer's disease or mild cognitive impairment
Nov.
11, 2009 - Older people with weaker muscles appear to
have a higher risk for Alzheimer's disease and declines in cognitive
function over time, according to a report in the November issue of Archives of Neurology, one of the JAMA/Archives journals.
Alzheimer's disease is characterized by declines in
memory and other cognitive (thinking, learning and memory) functions,
according to background information in the article. However, it is also
associated with other features, such as impaired gait and other motor
functions, depression and decreased grip strength.
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Patricia A. Boyle, Ph.D., and colleagues at Rush
University Medical Center, Chicago, studied 970 older adults (average
age 80.3) who did not have dementia at their initial evaluation.
Each participant underwent a structured initial
evaluation that included a medical history, 21 tests of cognitive
function, neurologic and neuropsychological evaluations and a composite
measure of muscle strength derived from testing in 11 muscle groups.
During an average of 3.6 years of follow-up, each
participant completed at least one additional identical evaluation.
Over the study period, 138 participants (14.2
percent) developed Alzheimer's disease.
Muscle strength scores ranged from -1.6 to 3.3
units; for each one-unit increase at the beginning of the study, older
adults had about a 43 percent decrease in the risk of developing
Alzheimer's disease during follow-up.
Those at the 90th percentile of muscle strength had
about a 61 percent reduced risk of developing Alzheimer's disease
compared with those in the 10th percentile.
The association between muscle strength and risk
for Alzheimer's disease remained even after other factors, including
body mass index and physical activity level, were considered.
"Because Alzheimer's disease develops slowly over
many years and its hallmark is change in cognitive function, we examined
the association of muscle strength with cognitive decline," the authors
write. Individuals who were stronger at the beginning of the study
experienced a slower rate of decline.
"Finally, in an analysis that excluded participants
with dementia or mild cognitive impairment at baseline, muscle strength
was associated with the risk of developing mild cognitive impairment,
the earliest manifestation of cognitive impairment," the authors write.
"Overall, these data show that greater muscle
strength is associated with a decreased risk of developing Alzheimer's
disease and mild cognitive impairment and suggest that a common
pathogenesis may underlie loss of muscle strength and cognition in
aging."
The basis for this association is unknown, they
note. Possibilities include damage to the mitochondria, which produce
energy for the body's cells, that may contribute to loss of both muscle
strength and cognitive function. Alternatively, decreased strength could
result from stroke or other disorders of the central nervous system that
also may reveal subclinical Alzheimer's disease.
