Decreased Muscle Strength May Increase Risk for Alzheimer's Disease and Cognitive Decline

November 10, 2009

In older patients, decreased muscle strength is related to an increased risk for Alzheimer's disease and mild cognitive impairment.

Older patients with more muscle weakness are at a higher risk of developing Alzheimer’s disease (AD) and mild cognitive impairment, researchers at Rush University in Chicago have found.

The muscle strength scores of the 970 participants ranged from -1.6 to 3.3 units. Altogether, 138 of participants, or 14.2%, developed AD. For each one-unit increase in muscle strength from the start of the study, patients were at a 43% decreased chance for developing AD. Participants who were in the 90th percentile for muscle strength were at a 61% reduced risk for developing AD compared to patients who were in the 10th percentile. The study also showed that muscle strength was associated with the development of mild cognitive impairment, the earliest signs of AD, and that cognitive decline was increased in patients with a lesser degree of muscle strength.

Patricia Boyle, PhD, a researcher in the Rush Alzheimer’s Disease Center, and her colleagues examined the 970 older adults, who had an average age of 80.3 and did not present with dementia during the initial evaluation, which involved 21 tests for cognitive function, neurologic exams, and measurements of strength in 11 muscle groups. Over the follow-up period, which averaged about 3.6 years, every participant was given at least one follow-up evaluation.

“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.”

Boyle also said that the association between muscle strength and cognitive decline may have a “complex” basis. One explanation may be “damage to the energy-producing mitochondria in the body’s cells, which may contribute to loss of both muscle strength and cognitive function.” Alternatively, according to Boyle, another theory may be that “decreased strength could result from stroke or other disorders of the central nervous system that may unmask subclinical Alzheimer’s disease.”

Findings of the study were also published in the November 9 issue of Archives of Neurology.