NEW YORK - Vigorous running — faster than 11 km an hour, more than 2.4 hours a week, more than three times a week — could be almost as harmful as sitting around doing nothing, according to a new cardiology study that’s likely to stoke the debate over how much exercise is too much.
The paper, published recently in the Journal of the American College of Cardiology, suggests there may be a point at which exertion becomes dangerous, outweighing the benefits of exercise. While the study didn’t specify how strenuous running could hurt people, researchers noted the stress that intense exercise can put on the cardiovascular system.
Previous research has shown that taxing workouts may put excessive strain on the heart, though plenty of studies have also underscored the many health benefits of exercise.
Researchers in the paper looked at 5,048 people in the Copenhagen City Heart Study, a long-term examination of thousands of people that has been the basis for many reports on cardiovascular health. The researchers sifted 12 years’ worth of data on 1,098 healthy joggers and 413 healthy but sedentary nonjoggers. The study looked at jogging hours and frequency as well as the person’s perception of how fast they ran.
The data excluded participants who were already diagnosed with heart disease, stroke or diabetes to control for self- selection bias, and scientists repeated the analysis excluding all deaths within the first two years of follow-up and found similar results.
The researchers found those who jogged one to 2.4 hours a week at a slow or average pace with no more than three running days in a week had the best survival rates. Anything longer than that left runners with death rates closer to those who didn’t run at all, the authors said.
“(Almost 2½) hours of exercise is ridiculous if you’re trying to qualify for the Boston Marathon,” said study co-author James O’Keefe. “But if you’re trying to live to be 90 and still have a good heart and still have good health, that’s probably an ideal amount of exercise.”
David Bach, a cardiologist and avid runner who has completed more than 35 marathons and several ultramarathons, cautioned that the findings may not paint a complete picture.
“I’m far from convinced based on data from this paper and other papers that there’s an actual increase in cardiovascular risk with higher levels of physical activity,” said Bach, a professor of medicine at the University of Michigan in Ann Arbor. “If this paper showed what it pretends to show — that running four hours a week is potentially detrimental — that is putting a very low lid on what is acceptable.”
Still, previous studies have hinted that moderate jogging may be the healthiest option. Running appears to lower the risk for mortality when an athlete doesn’t exceed more than 32 km a week, log more than 8 to 11 km per hour, or run more than two to five times a week, researchers at the Ochsner Health System of New Orleans and the University of South Carolina found in a 2012 paper.
It’s important for people not to selectively use the latest research as a reason not to exercise, when conditions that afflict sedentary people, like obesity and diabetes, are so prevalent, Bach said. More than one-third of U.S. adults are obese, and the number of diabetics surged to 19.6 million in 2011 from 5.5 million in 1980.
“I don’t think we’re facing some sort of medical crisis in this country because people exercise,” he said.
In the recent study, the researchers found that compared with sedentary non-joggers, runners who moved at a slow pace were associated with a 49 percent lower risk of dying.
Jogging at an average pace had a 62 percent decreased risk, said study co-author Jacob Marott, a statistician with the Copenhagen City Heart Study. Those who ran fast only had a 6 percent lower risk of dying. A slow and average pace was considered about 8 kph, while a fast pace was more than 11 kph, he said.
For those who ran one hour to 2.4 hours a week, the risk of dying was 71 percent lower than those who didn’t exercise.
“With most things in life there is a sweet spot, a middle zone that is ideal,” said O’Keefe, a sports cardiologist at Saint Luke’s Mid America Heart Institute in Kansas City, Missouri. “Moderation is best because it’s a long slog through life.”
Only 28 joggers and 128 of the non-joggers in the study died. Because of the small numbers, researchers weren’t able to statistically report the different causes of deaths, Marott said. The joggers in the study in general were younger, had lower blood pressure and body mass index and a lower prevalence of smoking.
Duck-chul Lee, who wrote an accompanying editorial, said more studies are needed to look specifically at heart-related deaths and outcomes in those who engage in vigorous exercise from running to cycling to skiing.
He cautioned that since the paper had so few people who died, particularly among vigorous runners, it limits the findings.