Their study is published in the November 9 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, PhD, 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 followup period, which averaged 3.6 years after the initial assessment, each participant completed at least one additional 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, and for each one-unit increase at the beginning of the study, participants had about a 43-percent decrease in the risk of developing Alzheimer’s disease at followup. Individuals in 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 significant even after adjustment for many other potentially important factors, including body mass index and physical activity level.
The researchers found a similar 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.
Other researchers at Rush involved in the study were Dr. Aron Buchman, Robert Wilson, PhD, Sue Leurgans, PhD, and Dr. David Bennett. The study was funded by grants from the National I