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A review study just came out in the British Journal of Sports Medicine about running and mortality risk. You may have seen a headline somewhere touting running’s seemingly magical power to reduce risk of death. That’s awesome! Any study that confirms my biases is a good study by me.
But as always with these big studies talked about on CNN, it’s important to remember the old quote attributed to Mark Twain. There are three types of lies: lies, damned lies and statistics. Does that apply here?
Digging down into the study, the authors acknowledge some potential limitations that may give you pause. First, an overview. If listening to someone talk about a scientific study makes you want to die, this may reverse any of running’s benefits.
Sexy Study Overview
The authors did a massive search of articles related to mortality and running, narrowing it down to 14 that fit their criteria, limited by being a prospective cohort study. In other words, studies had to look forward with participants reporting physical activity, rather than looking backward. In total, there were 232,149 participants, or slightly more than the population of Boise, Idaho.
So the various studies started with a Boise-full of participants, asked them a few questions, and waited for them to die (among other things). When you really think about it, that’s a good metaphor for life generally.
And here’s the most fascinating training part for our purposes. There was no statistically significant dose-response relationship. It didn’t matter how much participants ran or how fast they ran.
Over follow-up windows ranging from 5.5 to 35 years across the 14 studies, 25,951 people died. Boise lost some good people. Here’s the cool statistical part. Just knowing the death rates, the studies can control for variables to measure how running behavior influences all-cause mortality. The review found a 27-percent reduced risk of all-cause mortality for runners, a 30-percent reduced risk of cardiovascular death and a 23-percent reduced risk of cancer death.
And here’s the most fascinating training part for our purposes. There was no statistically significant dose-response relationship. It didn’t matter how much participants ran or how fast they ran. Running one time a week just above walking pace was enough to see the benefits. To quote Keanu Reeves, WHOA.
Less Sexy Details
It’s important to go past the abstract though, because that’s where we find the juicy stuff. A 2015 study in the Journal of the American College of Cardiology theorized a U-shaped curve of running and mortality risk, with benefits peaking and possibly reversing with heavier training. While that hasn’t been proven, it’s probable that there is an ideal running dose for each individual.
Think about it intuitively. Running has obvious benefits for the heart, lungs, bones and muscles. But it also is a stressor, and, at the cellular level, the sources of stress are not interpreted all that differently. Plus, there are likely diminishing returns for the cardiovascular system (i.e. possible cardiac issues) and musculoskeletal system (i.e. stress injuries). We know from other studies that excess stress increases all-cause mortality rates. If and where those curves intersect probably varies a ton based on the person.
Another important factor may be genetics and genetic expression. Perhaps the study is measuring an epigenetic influence, where any amount of running turns on genes that decrease mortality risk. Maybe all that effect requires is a bit of running. Maybe a ton of running turns on genes that increase negative risk in other areas. There are a lot of maybes in this paragraph because genetics are weird and may not always follow the correlation-causation rules we expect.
That gets back to how these population studies actually work. While we know the mortality rates from the studies, we don’t always know the underlying mechanisms of action. There are controls in the studies, but they can’t catch everything. Perhaps even with the controls, running is partially a proxy for a person being healthy and motivated enough to run. In that framework, the message wouldn’t be “run not to die,” but “run to prove you are still alive.”
Running for Life
Fortunately, there are also twin studies that control for genetic variation that show physical activity likely increases longevity. The question that is unanswered is whether running is the best activity for that goal, how much running is best for that goal and whether that goal should be the focus of athletic decisions anyway.
And that’s the point I’ll end with. There are lots of reasons to run. Adventure, exploring limits, daily purpose, experiencing mundane beauty. This new study shows that another reason might be reducing mortality risk. But you’re still going to die. Sooner rather than later if you zoom out far enough. You have little control over when and how that happens in the big scheme of things.
So make sure you are actually living while you are here. Runners have slightly less of a chance of dying in the next 5.5 to 35 years, but every resident in Boise has the same fate eventually. Run because you love the process, and all that other stuff will sort itself out in due time.
David Roche partners with runners of all abilities through his coaching service, Some Work, All Play. His book, The Happy Runner, is about moving toward unconditional self-acceptance in a running life, and it’s available now on Amazon.