"I think this can be taken as a real positive message," said Dr. James O'Keefe, the head of preventive cardiology at the Mid America Heart Institute in Kansas City and one of the researchers of the study.
"If you're trying to exercise for longevity, you don't need to be setting records."
The study used data from the Copenhagen City Heart Study, which collected information from nearly 20,000 people over several decades.
Researchers wanted to know if running lowered mortality rates. They concluded that it does — joggers reduced mortality rates by 30 per cent overall, and by 45 per cent for cardiovascular mortality specifically.
But those benefits decreased as the runners picked up speed.
'No better off than doing nothing'
"The people who got the best bang for their buck were the light to moderate runners," said O'Keefe.
"The strenuous joggers, the ones who were really hammering away for decades, at high mileage and high speeds, weren't really better off than the people doing nothing."
The study defined strenuous running as faster than five mph, more often than three times a week.
O'Keefe says strenuous exercise might expedite aging in the heart, increase scarring, and accelerate plaque buildup in arteries.
The risk increased with age and with frequency over time. Occasionally training for a fitness goal, however, wasn't as much of an issue.
"If you want to do one marathon in your life, go for it," said O'Keefe. "It's not going to kill you."
O'Keefe emphasizes that sedentary lifestyles are a more common issue for longevity.
"The bigger problem in Canada and in America is too many sedentary people," said O'Keefe. "The number of people who are really overdoing it, it's probably someplace under five per cent."
To hear more about the benefits of slow running, click on the audio clip labelled: Slow joggers live longer