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TUESDAY, Nov. 10 (HealthDay News) -- Elderly people with weak muscles may be at increased risk for Alzheimer's disease, according to a new study.

Researchers at Rush University Medical Center in Chicago followed 970 older adults (average age 80) who didn't have dementia at the start of the study. The participants underwent a number of evaluations, including tests of cognitive function and muscle strength.

During an average 3.6 years of follow-up, 138 (14.2 percent) of the participants developed Alzheimer's disease. Those with the highest levels of muscle strength at the start of the study were 61 percent less likely to develop Alzheimer's than those with the weakest muscles, the researchers found.

The link between muscle strength and Alzheimer's remained even after the researchers accounted for other factors, such as body mass index and physical activity levels.

The researchers also found that weak muscles were associated with increased risk of mild cognitive impairment, the earliest sign of cognitive decline.

"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," wrote study author Patricia A. Boyle and colleagues.

Although the reason for the association between muscle strength and Alzheimer's risk isn't known, the study authors noted that there are a number of possibilities. Damage to the mitochondria, which produce energy for cells, may contribute to loss of both muscle strength and cognitive function. A second possibility is that decreased strength could be caused by stroke or other central nervous system disorders that also may reveal subclinical Alzheimer's disease, they suggested.

The study appears in the November issue of the journal Archives of Neurology.

More information

The U.S. National Institute on Aging has more about Alzheimer's disease.