Reduced Muscle Strength Associated With Risk For Alzheimer's Disease

November 10, 2009

Adapted from the Rush University Medical Center

Seniors with weaker muscles appear to have a higher risk of developing Alzheimer’s disease and mild cognitive impairment, as well as a more rapid rate of cognitive decline, according to researchers at Rush University Medical Center.

Their study is published in the November 9, 2009 issue of Archives of Neurology.

“Our findings suggest that impaired muscle strength precedes the development of cognitive impairment in aging, and may be an early clinical marker,” said Patricia Boyle, Ph.D., a researcher in the Rush Alzheimer’s Disease Center. “However, decreased strength may not be a true risk factor. Rather, loss of muscle strength may be the result of an underlying disease process that also leads to cognitive decline and clinical symptoms of Alzheimer’s.”

Alzheimer’s disease is characterized by deterioration in cognitive functions, such as thinking, learning and memory. It is also associated with non-cognitive signs, such as impaired gait and other motor functions, depression and decreased grip strength.

Boyle and her colleagues studied 970 older adults (average age 80.3) who did not have dementia at their initial evaluation, which included 21 tests of cognitive function, neurologic exams and measurements of muscle strength in 11 muscle groups. During the follow up period, which averaged 3.6 years after the initial assessment, each participant completed at least one additional evaluation.

The researchers found an association between muscle strength and the risk of developing mild cognitive impairment, the earliest sign of Alzheimer’s disease. That finding suggests that assessment of muscle strength may be a useful clinical tool for early identification of individuals at risk for cognitive problems, who might benefit most from medical or other interventions, Boyle said.

The study also reported that the course of cognitive decline was more rapid in individuals with weaker muscle strength. Individuals who were stronger at the beginning of the study experienced a slower rate of decline.

According to Boyle, the basis for the association between muscle strength and cognitive decline is likely complex. Possibilities include damage to the energy-producing mitochondria in the body’s cells, which may contribute to loss of both muscle strength and cognitive function. Alternatively, she said, decreased strength could result from stroke or other disorders of the central nervous system that may unmask subclinical Alzheimer’s disease.

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