Even people in their 80s may be able to lower the risk of Alzheimer’s simply by increasing how much they move around each day, a new study suggests.

In a four-year study of 716 elderly Americans, researchers found that the least active seniors were more than twice as likely to develop Alzheimer’s disease compared to the most active.

Seniors’ activity levels were measured with an actigraph, a watch-sized device worn on the wrist that detects movements all through the day and night.

Intriguingly, much of the movement measured by the actigraphs came from regular daily activities, such as cooking, washing dishes, or cleaning, rather than formal exercise, said the study’s lead author, Dr. Aron Buchman, a professor of neurological sciences at the Rush Alzheimer’s Disease Center at the Rush University Medical Center.

The take home message, Buchman said, is that even people who have disabilities that prevent them from exercising can benefit just by making sure they move around a lot. “So even if you’re housebound, you may benefit from increasing whatever you do in the house,” he added.

An Alzheimer’s expert who is unaffiliated with the new study called the results “a fabulous finding.”

“I think this study is very simple and it has a very simple and very clear message: move more,” said Dr. Steven Arnold, a professor of psychiatry and neurology at the University of Pennsylvania and director of the Penn Memory Center. “The bottom line is that people who tend to be more active than others have a lower risk.”

For the new study, Buchman and his colleagues asked 716 volunteers without dementia to wear an actigraph on their non-dominant wrist continuously for 10 days. The volunteers had an average age of 82.

The volunteers were given annual cognitive tests to measure memory and thinking abilities. They were also asked to fill out surveys that asked about physical and social activities.

Because the new research is part of a larger, ongoing long-term study, Buchman and his colleagues also had information on volunteers’ health before the activity measurements.  “There was no association between activity level and prior rate of cognitive decline,” Buchman said. “So it’s not like people with low activity were already on a trajectory toward dementia or more rapid cognitive decline.”

Four years after the volunteers had done the actigraph experiment, 71 had developed dementia. When the researchers compared physical activity of the volunteers, they determined that those in the bottom 10 percent of intensity of physical activity were 2.8 times as likely to develop Alzheimer’s disease compared to those in the top 10 percent. And those results held up even when the researchers accounted for factors such as age, gender, chronic illness and depression.

Arnold isn’t surprised to see that risk went down with the intensity of physical activity. Animal studies have shown that the brain actually makes new cells when animals exercise. But that’s only when the animals choose to exercise, Arnold said.

“It’s interesting that if the mouse is forced to run on a wheel, it doesn’t have as good an effect as when the exercise is voluntary,” Arnold said. “Usually if you put them on a wheel they’ll just run for fun.”