Ask Doctor K

DEAR DOCTOR K: You say that physical exercise helps to improve brain health, but it's not obvious to me how that could be. Do researchers understand exactly how exercise helps the brain?

DEAR READER: I understand why that's puzzling. It's easier to see how regular moderate exercise could protect against heart disease, for example. The heart is a muscle, and exercise makes the heart exercise.

But the brain? We don't think of exercise as requiring a lot of brainpower. In fact, some people like exercise because it's a time when they can turn off their brain.

First, what's the evidence that regular exercise does protect the brain? There are many studies. As an example, a study published in February 2016 in the journal Neurology links better cardiovascular fitness to improved thinking skills in older adults.

The study included 877 adults with an average age of 65 years. Researchers used a measure called "VO2 max" to assess their fitness. This is the maximum amount of oxygen your body uses while you're exercising as hard as you can.

Study participants also took a variety of tests to gauge their thinking skills, memory and executive function. (Executive function is a term for mental skills used to manage time, plan and organize, and remember details.)

The researchers divided the participants into four groups based on their VO2 max values. They found striking differences in executive function between those with the highest and lowest VO2 max levels. In fact, those with the lowest VO2 max scores tested about seven years older than those with the highest VO2 max scores.

The trends were similar for memory and overall thinking ability. These corresponded to age differences of six and four years, respectively. In each area measured, higher fitness matched up to stronger cognitive skills.

How does exercise contribute to brain health? We know of several ways, and there are surely more we haven't yet discovered. One possible way is by improving the blood supply to the brain.

For the brain to get an optimal blood supply, it needs two things. First, a healthy heart to pump blood to the brain efficiently. Second, brain arteries that haven't been narrowed by atherosclerosis, and therefore deliver blood to the brain efficiently. Regular exercise strengthens the heart and reduces the risk of developing atherosclerosis.

Exercise also stimulates the growth of new blood vessels in the brain, and fuels the growth and survival of new brain cells. It does this by stimulating the production in the brain of natural chemicals that encourage new brain cells to develop and that keep older brain cells healthy. Brain-imaging studies suggest that key brain areas responsible for thinking and memory are larger in people who exercise than in those who don't.

How much exercise do you need to keep body and mind working well? Two hours and 30 minutes per week of moderate-intensity aerobic activity, or one hour and 15 minutes of vigorous-intensity activity help keep your heart fit. And your brain fit, too.

More like Ask Doctor K