Researchers from the Rush University Medical Center in Chicago have wrapped up a comprehensive 20-year study showing a possible causal link between a sedentary lifestyle and the deterioration of brain power and memory.

Examining the behaviour of 454 elderly adults over the course of of two decades, the study, which included yearly physicals, cognitive and memory tests, found that regular physical activity, such as walks or even just household chores, could significantly improve memory and cognitive function.

191 of the study participants suffered from dementia, while the rest did not. Late in their lives, participants were fitted with a device known as an accelerometer, which they wore on their wrists. The device monitored physical activity, including everything from walking around the house to regular exercise, on a round the-clock basis. Later, after death, scientists studied participants' brain tissue in autopsies, discovering that movement had a "protective effect on the brain."

Calculating an "average daily activity score", measured in "counts per day", the researchers found that participants who had the most active lifestyles almost invariably had better thinking and memory abilities than those who lived a sedentary lifestyle.

Just as significantly, the study found that even if a participant suffered from dementia, the more physical activity they engaged in, the better their thinking and memory skills would be. Researchers determined that even a marginal boost in physical activity has the potential to reduce the chances of dementia by a whopping 31 percent.

"People who moved more had better thinking and memory skills compared to those who didn't move much at all," study co-author Dr. Aron Buchman said. "We found movement may essentially provide a reserve to help maintain thinking and memory skills when there are signs of dementia present in the brain," he added.

Urging caution regarding the study's results, Dr. Buchman noted that while exercise "may have a protective effect on the brain," the study "does not show cause and effect."

"It may also be possible that as people lose memory and thinking skills, they reduce their physical activity. More studies are needed to determine if moving more is truly beneficial to the brain," he said.

One limitation of the study included the fact that researchers did not have information on how active participants were in their earlier lives.

Commenting on the implications of the research, Dr. Keith Fargo, director of outreach at the US Alzheimer's Association, said it was never too early (or to late) to exercise to keep up brain function. "The time to really begin thinking seriously about your brain health to have the best outcome is, if not your entire life, at least by early middle age," he noted.

Dr. Buchman et al's study was published in the 16 January 2019 online issue of Neurology.