By Amy Norton
The study found that seniors who got moderate to intense exercise retained more of their mental skills over the next five years, versus older adults who got light exercise or none at all.
On average, those less-active seniors showed an extra 10 years of "brain aging," the researchers said.
The findings do not prove that exercise itself slows brain aging, cautioned senior researcher Dr. Clinton Wright, a neurologist at the University of Miami Miller School of Medicine.
It's possible, he said, that there are other reasons why active older adults stayed mentally sharper.
And exercise levels were still connected to the participants' performance on tests of memory and "processing speed" -- the ability to digest a bit of new information, then respond to it.
Plus, Wright said, it's plausible that exercise would affect those mental skills. Other research has shown that physical activity boosts blood flow to the brain, and may enhance the connections among brain cells, for example.
Exercise can also help manage "vascular risk factors," such as high blood pressure, unhealthy cholesterol levels and diabetes, Wright pointed out.
The new study findings were published March 23 in the journal Neurology.
Dr. Ezriel Kornel, a neurosurgeon who was not involved in the study, agreed that the findings don't prove that exercise will keep you thinking clearly.
"It could simply be that people who are drawn to exercise are also at lower risk of cognitive decline," said Kornel, a clinical assistant professor of neurological surgery at Weill Cornell Medical College, in New York City.
That said, he called the study "important," because it at least suggests that exercise could have a big impact on people's mental function as they age.
"We already know that exercise is highly valuable for cardiovascular health," Kornel said.
The potential to add extra years of healthy brain function might motivate more people to get moving, he said.
The findings are based on nearly 900 older adults who took standard tests of memory, attention and other mental skills at an average age of 71. They repeated the tests five years later. At the time of the first test, they also underwent MRI scans of the brain, which allowed the researchers to look for changes associated with early mental impairment.
Overall, 10 percent of the group said they regularly got moderate to high-intensity exercise -- which meant activities such as jogging, aerobics and calisthenics.
It turned out that those men and women showed substantially less mental decline over five years than the rest of the group -- who were either sedentary or got light exercise, like walking.
When it came to tests of episodic memory -- remembering words from a list -- less-active and sedentary seniors showed the equivalent of 10 extra years of brain aging.
According to Wright, the results suggest that a casual walk around your neighborhood is not enough to preserve brain function as you age.
"It seems like we're not going to get off easy," he said. "There's increasing evidence that it needs to be exercise that gets your heart rate up."
However, Wright added, the necessary exercise regimen is far from clear. Seeking some answers, his team is running a trial testing the effects of exercise on stroke survivors' brain function over time.
According to Kornel, exercise could theoretically benefit the brain in a range of ways. "Improved blood flow to the brain is one logical assumption," he said.
But, he added, exercise can also keep people mentally engaged -- by making them learn new things or concentrate, for example. And if you exercise with other people, Kornel noted, there's a social aspect, too.
"If you're out in the world, physically active, there are many things going on that are probably not happening when you're just sitting on your sofa," he said.