And the fitter they stayed physically, the more mentally fit they were in middle age, according to the study published in the journal Neurology.
“Many studies show the benefits to the brain of good heart health,” said David Jacobs of the University of Minnesota, who designed and led the study. “This is one more important study that should remind young adults of the brain health benefits of cardio fitness activities such as running, swimming, biking or cardio fitness classes.”
It’s known that exercise can boost brain power, but Jacobs and colleagues correlated fitness directly with thinking skills later in life — right down to how many minutes people can last doing a punishing treadmill exercise.
“The longer you could go on this treadmill test... the better you did in thinking skills,” Jacobs said in a telephone interview.
The study started back in 1985 when the researchers recruited about 5,000 people aged 18 to 30 in Minneapolis, Birmingham, Ala., Chicago and Oakland, Calif. They did the treadmill test and got physical examinations. Many of the people had interim examinations, and more than 2,700 agreed to try the treadmill test again 20 years later.
“The longer you could go on this treadmill test… the better you did in thinking skills."
Almost everyone was at least a little less fit. Five years later, they also underwent a battery of three types of brain test — a word recall test, a number-based test of attention, thinking speed and memory, and a test of executive function that looks at how people can focus while tuning out distractions.
The better people did on the treadmill test 20 years before, the better they did on the memory test. And if people had kept their fitness up in middle age, they did even better.
Those who were fit in their 20s were healthier in all sorts of ways — they weighed less, ate a better diet, were less likely to smoke and more likely to exercise. They were also on average better educated and watched less TV. But even accounting for this, the fitter people did better on the thinking tests.
It fits in with other research, including another study out this week that showed young adults who have better heart health, as measured by blood pressure, have better thinking skills in middle age than those with high blood pressure.
That study, done by researchers at the University of California, San Francisco also used three tests of memory and thinking and it also accounted for weight, sex, drinking, smoking and education.
One reason is that the brain uses a lot of oxygen, and people who are fitter make more efficient use of oxygen, Jacobs said. Physical activity also benefits mitochondrial function — a measure of how well structures in the cells call mitochondria make use of energy.
"This is really about engagement in life.”
Many people dropped out of the exercise part of the study and Jacobs suspects these would have been those who were at the lower end of fitness. Having them in the study would have produced clearer results, but wouldn’t have changed the trend, he says.
Other studies have shown that if you are fit in middle age, you will preserve your brain power better. But Jacobs said it may be too late to start getting fit by the time you’re middle-aged. His study supports the idea that it’s important to develop good fitness habits early.
There is more going on than just exercise, Jacobs says. “Just moving around — being engaged in family and life as opposed to sitting down and watching TV and pretty much not doing anything, they are going to preserve brain function. This is really about engagement in life,” he said.
The team wants to keep on watching the group to see if those who were less fit in their youth are also less likely to develop Alzheimer’s.
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