People who are physically active in their older years may lower their risk of developing Alzheimer's disease, a new study suggests.

The results show that people in the bottom 10 percent of daily physical activity were 2.3 times more likely to develop Alzheimer's disease over a 3.5 year period, compared with people in the top 10 percent of daily activity.

“The results of our study indicate that all physical activities — including exercise as well as other activities such as cooking, washing the dishes and cleaning — are associated with a reduced risk of Alzheimer's disease,” study researcher Dr. Aron S. Buchman, an associate professor of neurological sciences at Rush University Medical Center, said in a statement.

The findings are inline with those of previous studies that have also suggested a link between increased physical activity and a reduced risk of Alzheimer's. The new study is different from others in that researchers included an objective measurement of people's activity levels, Buchman said.

The study included 716 older people, whose average age 82. Participants wore a device called an actigraph, which monitors movement and activity, on their non-dominant wrist continuously for 10 days. Participants also reported their physical and social activities.

The participants also took annual cognitive tests to measure memory and thinking abilities. None of the study participants had dementia at the study's start.

Over the 3.5 year study, 71 participants develop Alzheimer's.

The intensity of a person's physical activity also made a difference in the risk of developing Alzheimer's, according to the study. The people in the bottom 10 percent of intensity of physical activity were 2.8 times as likely to develop Alzheimer's disease as people in the top percent of the intensity of physical activity.

Still, because the actigraph was worn on the write, activities such as cook and playing cards were beneficial, Buchman said.

“These results provide support for efforts to encourage all types of physical activity even in very old adults who might not be able to participate in formal exercise, but can still benefit from a more active lifestyle,” Buchman said.

One in eight people in the U.S. over age 65 has Alzheimer's disease. The number of Americans older than 65 years of age will reach nearly 80 million by 2030, according to the study.

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“Our study shows that physical activity, which is an easily modifiable risk factor, is associated with cognitive decline and Alzheimer's disease. This has important public health consequences,” Buchman said.

The study is published on line Wednesday (April 18) in the journal Neurology.

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