A blog by runners. For runners.

Study: Can running too much kill you? (and how to properly read studies)

Can running too much kill you?

In grad school for my Master of Public Health, we had to take several courses learning how to properly interpret scientific studies – and how to tell the good studies from the not-so-good ones. (Bear with me. I promise this has to do with running.)

One of the most important lessons we learned was that correlation does not equal causation. Let’s say we have a group of people who ate one apple every day, and we compared them to a control group who didn’t eat any apples. Say we were measuring doctor visits, and we found that the non-apple eaters had significantly more doctor visits than the apple eaters. Could we conclude that an apple a day keeps the doctor away?

No. We could only say eating apples is linked with fewer doctor visits according to one study. Just because the apple eaters didn’t go to the doctor as much doesn’t mean it was the apple that lead to fewer appointments. There could be other factors that we didn’t measure that made the non-apple eaters unhealthier. Or the apple eaters could have been a healthier group to begin with. Or the apple eaters were just as sick but decided not to go to the doctor.

This is why studies have to be repeated many times before experts can say links exist. For instance, there have been thousands of studies and tons of medical data on smoking cigarettes and lung cancer that experts are confident there’s a link.

But when you hear blurbs of studies in the news, there’s often not that much data to back them up.

Last week, I came across this headline: Too much running tied to shorter lifespan, studies find.

The study authors presented their findings at the American College of Cardiology’s annual meeting in Washington, DC last month. The paper isn’t published yet, but here’s the abstract.

“The researchers behind the newest study on the issue (running and health) say people who get either no exercise or high-mileage runners both tend to have shorter lifespans than moderate runners. But the reasons why remain unclear,” they added.

This is an interesting spin. For one, the data was self-reported (meaning that it usually comes with bias) in an online survey called the MASTERS Running Study (here’s how you can participate in it). The survey asks several questions including how much you run, what type of pain relievers you take, if you smoke, and if you have high blood pressure, cholesterol, or other health issues.

They divided the survey participants into two groups: those who ran less than 20 miles per week and those who ran more than 20 miles per week. They found that the lower mileage runners were more likely to use NSAID anti-inflammatory painkillers, like Advil.

That’s it. The study didn’t follow up with participants to see how long they actually lived. So, why is the headline for this study “too much running tied to shorter lifespan”?

I don’t know. At the conference, the study authors hypothesized that the bodies of high-mileage runners have too much “wear and tear” and that the “sweet spot” for running is somewhere between 1- 2.5 hours per week at a slow to moderate pace. They came to this recommendation based on data from other studies.

I’m still lost. I’m not saying that the actual conclusion isn’t true. I believe that there is a threshold of too much running where it becomes dangerous to your health. In my non-expert opinion, though, I think that threshold is different for each runner. You’ll never catch me racking up 100 mile weeks because I know my body would fall apart, but that’s not to say you couldn’t handle it.

The next time a “running is bad” study comes across your desk, we encourage you to read the story and question it. Chances are running isn’t quite as dangerous for your health as the headline makes it out to be.

Written by Jen Matz.