The research says those who run moderate amounts have longer lives than those who don’t work out at all.
They also claim they outlive runners who pile on the marathon length miles.
HealthDay points out the work looked at nearly 4,000 runners, most of whom logged more than 20 miles per week on the paths.
A cardiologist who studied the results believes 2.5 hours of running over seven days may be the magic number.
The suggestion is to spread that over several days and to keep the intensity to a moderate pace.
Dr. Martin Matsumura from the Cardiovascular Research Institute at the Lehigh Valley Health Network led the study.
He admits the biggest mystery is why too much running is bad for you.
However, doctor and running coach Jason Karp thinks he may have an idea. Karp told NBC San Diego exercise as extreme as marathons can "cause some scarring of the heart."
The Pioneer Press also reports other recent research discovered something surprising. Male marathon runners actually had more plaque in their coronary arteries than non-runners.
One of the scientists summed the work up by saying, “it is plausible, not proof by any stretch, that metabolic changes when running could be moderately toxic to arteries."