Sorry, Running Doesn't Make You Live Longer

You may have heard that a recent study found an hour of running could add seven hours to your life. Proclaiming as much in a headline is often traffic gold: People click and share content that says their habit is good for them; runners especially so, and who doesn't want to live longer?

Problem is, the headline is at best misleadingly simplified; at worst, plain wrong.

Look, I love running. I've been a runner for more than 15 years and have finished a handful of marathons, even more half-marathons, and countless 5Ks. But the current study was an observational one, in which researchers analyzed self-reported data about one of people's many habits—exercise—and then drew an association between it and how long those people lived. There could be plenty of other reasons why people who run live longer than people who don't. Like maybe they're healthier to begin with and they eat well, or have good genes. It's not like they randomly assigned certain people to run and others to not run and then followed them for 40 years. (And even then, researchers really can't control people's diets and other habits that affect their health.)

Possibly even more importantly, there's a fun aside mentioned in parentheses in the New York Times coverage of this story, and not put into any context at all: Most of the the participants in the studies reviewed were white and middle class. If we learned anything last week, that's a big fucking caveat. Race and income are inextricably linked to health. People of color and people who make lower incomes don't live as long as people who are white and make more money. It's not accurate to draw broad conclusions based on studies of mostly white people.

Let's look more closely at the study. It was a review of past research that determined that runners live an average of three years longer than non-runners. This held true even if the runners smoke (a real phenomenon), drink, have high blood pressure, or are overweight, or if they run slowly. Other forms of exercise including walking and cycling also seemed to extend people's lives, but not by as much as running.

The seven hours thing came from a statistical calculation to see if running added more time to people's lives than the time it would take to actually run. The authors used an average of two hours a week of running reported in a 2014 study they conducted (which is included in this review), and estimated that, over about 40 years, people would spend less than six months running but could expect to increase their life expectancy by 3.2 years, which is a net gain of 2.8 years. I did the math and that's a gain of about 28,000 hours from 4,160 hours of running over 40 years, or 6.74 hours of life per hour of running. That's where the seven hours stat is from; really it's a net gain of 5.74 when you consider the time spent running, but I digress; there are bigger fish to fry here.

The New York Times loves to cover studies that say running is good for you and will help you live longer; this is just the latest one. They covered it on Wednesday and dozens of other sites have piled on in the last 48 hours. (Runner's World wrote it up on April 5 but it didn't reach shitstorm status until this week.) And the Times' coverage of the study has spawned headlines like these:

One Run May Add 7 Hours to Your Life, Study Says (Just one run? Try again.) 
This Exercise Can Add Years To Your Life (Yeah maybe it can, but there's no way to tell that running is what's responsible.)
It's official: Running is the best exercise you can do (Ok now you're just being crazy.)
It's official: This type of exercise adds the most years to your life (a baitier version of the above)

The Times piece does acknowledge that "running does not make people immortal" and the lifespan gains aren't infinite; the researchers said the increase in longevity gains plateau at about three years of life. They flatten out at about four hours of running per week and don't seem to decline, which is good: diminishing returns but not negative ones.

The takeaway here is to beware of any headline that suggests that one thing alone—like a certain food or kind of exercise—can help you live longer. Read the whole story. The Times does mention the issue of association versus causation, but only in the last two paragraphs:

How many articles do you read until the very last word?

Talking about the health benefits of exercise in ways that might encourage more people to do it is a good thing, and running is a pretty simple and cheap form of exercise, which makes it easy to start. But the problem here is the potential for people to think that they can run a little and counteract other things they're doing that are likely to shorten their lives (like those smokers). A majority of doctors would agree that to live a long, healthy live, you need to exercise, eat vegetables, don't smoke, and don't drink too much. You know, the boring shit that people don't click on.

Related:

Can You Tell if a Health Story is Total BS?

Running is the Worst Way to Get Fit

How Far Can We Push the Limits of Human Life?