"It's like a wristwatch and is pretty nonobtrusive," he said. "They wear it 24 hours a day."
The researchers then watched to see what happened to the participants. Over an average of almost four years, 71 developed signs of Alzheimer's disease. The researchers analyzed their statistics to see if the risk of the illness was higher or lower depending on the activity levels of the participants back when they wore the devices.
Those among the 10 percent of participants who were most active had an 8 percent likelihood of developing signs of Alzheimer's over the time period in which they were followed. The risk jumped to 18 percent among the 10 percent of participants who were the least active.
Buchman acknowledged that it's impossible to know which comes first: little activity or brain problems. "The whole issue of whether there's a causal relationship between physical activity and cognition is one that needs to be sorted out," he said.
One challenge to understanding the link between exercise and the brain is that an ideal study would need to assign some people to be more active and others to be less active. And, according to Dr. William Jagust, a professor of neuroscience at the Helen Wills Neuroscience Institute at the University of California, Berkeley, then they'd need to be followed for a long time to confirm whether activity (or lack of it) makes a difference.
The study appears online April 18 and in the April 24 print issue of Neurology.
The authors acknowledged some study limitations. Because the study volunteers included so many more women than men, the results might not apply to the population at large, they said. Also, the devices didn't distinguish among the different activities performed.
For more about Alzheimer's disease, see the U.S. National Library of Medicin
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