Couch potatoes everywhere were overjoyed to learn—courtesy of a recent study—that running is actually dangerous. But a closer look at the science suggests the smirks are seriously misguided.
A week ago, the Internet lit up with a headline that rocked runners. There were many variations, but it went something like this: Study suggests too much running causes shorter lifespan. The headline was wrong.
Anyone following the “how much is too much” debate might’ve thought the stories were reposted from 2012, when cardiologist James O’Keefe published an article in Mayo Clinic Proceedings claiming that long-term excessive endurance exercise—marathons, ultramarathons, Ironmans—may remodel the heart in a harmful way.
O’Keefe’s revelation garnered a lot of press, but it was a hypothesis with little science behind it. In fact, O’Keefe’s line of thought resembled something like a DirecTV commercial: When your cable company keeps you on hold, you get angry. When you’re angry, you go blow off steam. And so on and so forth until you end up in a roadside ditch.
The heart, O’Keefe explained to TIME, pumps about five quarts of blood per minute at rest. Running, it can pump 35 or 40 quarts per minute. Running for miles on end can overtax the heart. Overtaxing the heart can cause heart fibers to tear. Torn fibers will lead to scar tissue, which can lead to abnormal heart rhythms and a premature death.
It sounds logical, but O’Keefe’s reasoning and his conclusion that that running more than 20 miles per week could actually be bad for you were largely discounted by his contemporaries barring more solid scientific proof. One researcher I interviewed for Outside even called O’Keefe’s allegations “warmongering.”
So what’s up with last week’s headlines?
Nobody has said O’Keefe was flat-out wrong. Researchers generally agree with the idea that there is a threshold after which more exercise can have adverse health effects. What they don’t agree on is where that threshold lies, a fact that may take more than 10 years from now to discern. (Why? It takes thousands of subjects enrolled in a study over a decade or more to figure out something like the effect of endurance exercise on mortality.)
Last week’s headlines referred to ongoing research called the "Masters Running Study" that hopes to one day draw its own conclusions about running and mortality. But it hasn’t yet. That’s why the headlines are wrong.
Other studies, including O’Keefe’s research and the oft-cited "Copenhagen Heart Study," which included a 27-year jogging sub-study that analyzed data from 1,878 runners between 1976 and 2003, promoted the idea of a U-shaped curve relating time spent exercising and mortality.
The Copenhagen Heart “found that between one hour and two and a half hours a week, undertaken over two to three sessions, delivered the optimum benefits, especially when performed at a slow or average pace,” the European Society of Cardiology explained. Any more or less, and lifespan may decline, though researchers could not say exactly why (though many outside experts have noted serious flaws in the interpretation of the data).
The "Masters Running Study," an online survey (you can take it here) spearheaded by co-director of the Cardiovascular Research Institute at Allentown’s Lehigh Valley Health Network, Dr. Martin Matsumura, sought to explain why that U-shaped curve may exist—why people who run more than 20 miles per week could, according to O’Keefe and the Copenhagen study, shorten their lifespans.
Matsumura and his colleagues looked into whether or not NSAID use, medication, and cardiac risk factors such as hypertension, smoking, and diabetes played a role in creating that curve.
The results so far: a shorter lifespan in people who run more than 20 miles per week could not be explained by an increase in cardiac risk factors such as smoking, diabetes, hypertension, or a family history of coronary artery disease, because there wasn’t one; both sub-20 mile-per-week runners and higher volume runners had similar backgrounds. Nor could it be explained by an increase in NSAID use, because runners who ran less than 20 miles per week actually used them the most, or the use of other drugs like aspirin.
These results were recently presented at the at the American College of Cardiology's annual meeting in Washington, D.C., sparking the flurry of headlines cursing avid runners to an early death. Because none of the factors mentioned above could explain the curve, “that caused the media to interpret that sure enough, it must be running” that’s the culprit, Matsumura says. “But I still don’t think we know.”
Matsumura believes O’Keefe and the Copenhagen study draw conclusions about running and health that may not apply to today’s runners, as they began recruiting runners in the ‘70s.
“When you think back to runners in the ‘70s, I think training, diet, and education were different. The medical community didn’t really know how to approach runners,” Matsumura says. “Today’s runners are a very self-educated and proactive group. They know about nutrition and training. I think the contemporary runner is definitely a different beast than those 20, 30 years ago.”
In other words, while that U-shaped curve likely exists, it may not sharply peak at 2.5 hours or 20 miles of moderate jogging per week for today’s runners. The curve may be broader or peak later. And it may not be caused by the running but outside factors.
Matsumura and his colleagues hope more people will participate in the "Masters Running Study" and that, in another decade or so, he and his colleagues be able to draw more scientific conclusions about that curve and the effect of running on the modern runner’s mortality.
(It must be noted that it’s entirely possible that today’s “modern runner” will look like a Converse-wearing ‘70s runner to the runners of the future, and so this running-mortality, exercise-threshold, who-does-it-apply-to debate could beat on for all eternity.)
“We now have well over 5,000 runners recruited for this study,” Matsumura says. “We’ll be following them so we’ll know if they drop dead from running.”