Exercise is well known for strengthening the heart — but it may also be one of the simplest ways to boost brain health.

Research shows that regular physical activity can improve memory, sharpen thinking skills, and even help reduce depression. And the good news: you don’t need to run marathons to see benefits.

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"Certainly you don't have to be a triathlete. But it turns out walking is really important," Dr. Gary Small, director of behavioral health breakthrough therapies at Hackensack Meridian Health, told Newsmax’s "National Report."

In fact, a recent study offers encouraging news — especially for older adults.

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Researchers from Mass General Brigham followed nearly 300 healthy participants, ages 50 to 90, over nine years. They tracked their daily step counts and used scans to measure levels of amyloid-beta and tau tangles, two hallmarks of Alzheimer’s disease, in their brains. Participants also underwent annual cognitive assessments.

Cognitive decline was delayed by three years on average for people who walked just 3,000-5,000 steps per day, and by seven years in people who walked 5,000-7,500 steps per day, according to the study published in Nature Medicine.

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"The sweet spot was 3,000 to 5,000 steps a day," Small, author of The Small Guide to Alzheimer’s Disease, said. "That was associated with less of this abnormal tau protein that's linked to Alzheimer's disease and also less cognitive decline."

Getting more steps offered additional benefits — but only up to a point.

"Turns out if you go 7,500 steps a day, you do better. But beyond 7,500 steps, there's no added benefit," Small noted.

Beyond brain health, exercise also plays a powerful role in improving mood.

"When you go out, you take a brisk walk, it elevates a natural antidepressant in your body called endorphins," Small explained. "We've all heard that expression 'runner’s high' — and that’s what’s happening," said Small, who is also editor of Dr. Gary Small’s Mind Health Report.

Exercise may even lead to physical changes in the brain itself.

"When you walk, when you exercise, it makes your brain larger," Small said. "So it's not just the cognitive benefits, but it's also mood benefits that people are experiencing."

He added that exercise can also help reduce inflammation — another factor linked to aging and cognitive decline.

"You don’t need extreme workouts to protect your brain. A simple daily walk may go a long way toward keeping both your mind and mood in good shape."