More muscle power means lower Alzheimer's risk

NEW YORK (Reuters Health) - Older people with stronger muscles are at reduced risk of developing Alzheimer's disease compared to their weaker peers, a new study shows.

Dr. Patricia A. Boyle of Rush Alzheimer's Disease Center in Chicago and her colleagues found that the greater a person's muscle strength, the lower their likelihood of being diagnosed with Alzheimer's over a four-year period. The same was true for the loss of mental function that often precedes full-blown Alzheimer's.

Studies have linked grip strength to Alzheimer's, while a person's weight and level of physical activity also influence risk of the disease. To date, however, no one has studied whether muscle strength in and of itself might play a role in dementia risk, Boyle and her team note in November's Annals of Neurology.

"These findings support the link between physical health and cognition in aging and the importance of maintaining good physical function and strength," Boyle told Reuters Health via E-mail.

The researchers measured the strength of nine muscle groups in the arms and legs of 970 dementia-free men and women 54 to 100 years old (their average age was around 80). They also tested the strength of study participants' breathing muscles.

During follow-up, which lasted about four years, 138 people developed Alzheimer's. These individuals were older and had worse mental function than the rest of the study participants. They also were weaker.

But even after the researchers adjusted for age and education level-which can influence Alzheimer's risk-they found that muscle strength had a strong influence on the risk of the disease. People who ranked in the top 10 percent for muscle strength were 61 percent less likely to develop Alzheimer's than the weakest 10 percent. Stronger people also showed a slower decline in their mental abilities over time.

The relationship between muscle strength and mild mental difficulties, which occurred in an additional 275 people, was similar, with the strongest 10 percent being at 48 percent lower risk than the weakest 10 percent.

When the researchers looked at different types of muscle strength separately, they found that grip strength and breathing-muscle strength had an independent effect on Alzheimer's risk, but arm and leg strength didn't.

The most likely explanation for the mental function-muscle strength link is that there is something going in the body that causes both muscle weakness and loss of mental ability, Boyle said.

While the study couldn't show whether keeping one's muscles strong will keep Alzheimer's at bay, staying fit is a good idea-and good for the brain-no matter what, according to Boyle.

"We certainly think that it is important to be physically active and to work to keep our muscles strong," she said. "Good physical health is important for good brain function."

SOURCE: Archives of Neurology, November 2009.