Being physically active may boost the brain’s fight against the world’s No. 2 killer, according to new research.

About 795,000 Americans have a stroke each year, and 129,000 die. But exercising could lessen the severity of stroke later in life, according to research that will be published in the Journal of Cerebral Blood Flow and Metabolism.

Brain health depends on a network of blood vessels called collaterals. The more you have, the better — because collaterals carry blood to part of the heart when a coronary artery is blocked, or to part of the brain when a cerebral artery is blocked, providing protective benefits.

“You have collaterals in your heart, in your brain and in the muscle and skin of your legs and arms,” said James Faber, Ph.D., the study’s lead researcher and a professor in the department of cell biology and physiology at the University of North Carolina in Chapel Hill. “We’re quite interested in these collaterals in terms of stroke and heart disease.”

Since collaterals decline with aging, and strokes hit older people the hardest — killing more brain tissue — researchers set out to find out if exercise would prevent the loss of collaterals and reduce the effects of stroke.

Faber and his colleague Wojciech Rzechorzek, M.D., looked at collaterals in two groups of mice. One group was sedentary, while the other exercised regularly on running wheels.

The sedentary mice, who were 80 human years when they had a stroke, experienced large, severe strokes and lost a lot of brain tissue or collaterals. But the same-age running group fared much better. Their collaterals stayed steady and they had much less brain damage after a stroke.

“Besides the many reported benefits of regular physical activity, it is very possible that regular, brisk walking, jogging or running or any kind of aerobic exercise has an additional effect of keeping blood vessels young and abundant in the brain, heart and lower legs,” Faber said.

Previous studies showed that collaterals are very important in terms of prognosis for stroke patients. These new findings might also apply to people, meaning being physically fit could mitigate brain damage after a stroke, but more research is needed.

“If you have a stroke but you have a lot of these collaterals, that tissue will still get oxygen and nutrients. “If you have abundant collaterals, you could be eligible for a thrombectomy [which removes blood clots], which will benefit you,” he said. “But if you have poor collaterals, a thrombectomy won’t have a benefit.”

Barry Franklin, Ph.D., director of preventive cardiology and cardiac rehabilitation at William Beaumont Hospital in Royal Oak, Michigan, said the findings are promising.

“Recent studies using advanced technologies have suggested similar adaptations in the human heart as a result of exercise training,” said Franklin, who was not involved in the study. “These findings further reinforce the cardiovascular and protective benefits of regular exercise. He added that exercise pays off, even in spurts.

“Three 10-minute bouts equal the benefits of one 30-minute bout. I tell patients that when it comes to exercise, you don’t have to put the dollar bill in the piggy bank at one time,” Franklin said. “Four quarters, or even 10 dimes, will provide the same payoff.”

Stroke can cause death or disability, including memory, speech and vision loss; emotional problems and paralysis.