Run When You're 25 For A Sharper Brain When You're 45

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If you're in your 20s, you might work out because it's fun, or because it makes you look better. But here's another reason to hit the gym or go for a jog — exercising now may help preserve your memory and cognition later in life.

Researchers figured this out by following 2,700 men and women for 25 years as part of the Coronary Artery Risk Development in Young Adults Study.

Teenagers and young adults who did better on treadmill tests tended to do better on memory and problem solving tests in middle age, researchers found. That's even after they accounted for unhealthful things like smoking, diabetes and high cholesterol.

Young people don't always consider how their lifestyle might affect them 25 years down the road, says David Jacobs, a professor at the University of Minnesota's School of Public Health and one of researchers behind the study.

We already know that regular exercise helps stave off things like obesity and heart disease. And earlier studies have found that older adults who exercise are more likely to remain mentally sharp. But this study is one of the first to look at how exercise in young adulthood affects cognition.

The researchers don't know why exactly cardiovascular exercise helps preserve brain function. But they suspect it's because a healthy heart is better at pumping blood and oxygen to the brain.

"Things that would be good for the heart are probably going to be good for the brain," Jacobs says.

The effects on memory in this study were fairly small. On average, the least fit participants were able to remember seven out of 15 words in a memory test; the fittest participants were able to remember eight.

The researchers also had participants read out the names of colors printed in different colored ink to test executive function, and replace a series of numbers with symbols to gauge how well participants could coordinate their thinking with their actions. The fittest participants were on average four seconds quicker to read out the correct colors on the executive function test, and they were able to more accurately substitute symbols for numbers.

Jacobs realizes that doesn't sound impressive. "If a person can remember one more word on a list, so what?" he says. But an even a slightly sharper mind could give people an edge in their careers and ultimately in their quality of life, he says.

The findings were published Wednesday in the journal Neurology.

But what if you're past 50, and you didn't exercise when you were younger? Jacobs says there's no need to freak out. And there's no need to start training for a marathon right away, either.

However, Jacobs says, being active in middle age will very likely benefit your brain, no matter how buff you were in college. Study participants who were more fit in middle age than in their 20s had slightly better cognition than participants who weren't active in middle age.

"If you have not done everything exactly right — and that's pretty much everybody — you can make changes later in life," he says.