Can Running Kill You? (part 3)

The Too-Much-Running Myth Rises Again
Risks of an overdose are greatly exaggerated.
By
Alex Hutchinson
Published
November 28, 2012

Stop me if you've heard this one before, but... RUNNING TOO MUCH COULD KILL YOU!!! That's the message of a Wall Street Journal article that's making the rounds this week, based on a forthcoming editorial in the journal Heart. Sound familiar? It should, because someone writes an article with this message every few months, and it invariably rockets around the cybersphere powered by schadenfreude.

In this case, it should sound extra-familiar, because the Heart editorial is co-written by some of the same team that wrote "Cardiovascular damage resulting from chronic excessive endurance exercise" in July, and "Potential adverse cardiovascular effects from excessive endurance exercise" in June, not to mention last year's "Exercise like a hunter-gatherer: a prescription for organic physical fitness." As cardiologist Paul Thompson says in the WSJ piece, "The guys advancing the hypothesis that you can get too much exercise are manipulating the data... They have an agenda."

Of course, I have an agenda too. I like running, and that inevitably colors my perspective. I posted my thoughts on this topic in detail earlier this year, during one of the earlier iterations of this same debate (sparked by essentially the same article by James O'Keefe et al. in a different journal). As I said then, there's no doubt whatsoever that the health benefits of aerobic exercise eventually reach a point of diminishing returns. Where is that point? No one really knows, but my personal feeling is that if you're running more than an hour a day, you're doing it for reasons other than optimizing health. Which is fine. But crucially, that doesn't mean you're hurting your health by running an hour a day, and when people start making suggestions like that, I agree with Thompson that they're twisting the data. Two examples:

(1) One of the major pieces of evidence the group cites is a study that was presented at a conference over the summer. The WSJ description:

In a study involving 52,600 people followed for three decades, the runners in the group had a 19% lower death rate than nonrunners, according to the Heart editorial. But among the running cohort, those who ran a lot—more than 20 to 25 miles a week—lost that mortality advantage.

But here, from the actual abstract, is the part they never mention:

Cox regression was used to quantify the association between running and mortality after adjusting for baseline age, sex, examination year, body mass index, current smoking, heavy alcohol drinking, hypertension, hypercholesterolemia, parental CVD, and levels of other physical activities.

What this means is that they used statistical methods to effectively "equalize" everyone's weight, blood pressure, cholesterol, and so on. But this is absurd when you think about it. Why do we think running is good for health? In part because it plays a role in reducing weight, blood pressure, cholesterol, and so on (for more details on how this distorts the results, including evidence from other studies on how these statistical tricks hide real health benefits from much higher amounts of running, see my earlier blog entry). They're effectively saying, "If we ignore the known health benefits of greater amounts of aerobic exercise, then greater amounts of aerobic exercise don't have any health benefits."

(2) A minor example from the earlier review by this group in the Mayo Clinic Proceedings. Early in the article, they make this key statement:

A very large recent study found that [the benefits of endurance training] accrue in a dose-dependent fashion up to about an hour per day of vigorous physical activity, beyond which more endurance training does not yield further benefits.

So what happens if we actually dig up this "very large recent study" they refer to? Sure enough, the study, published in The Lancet, contains this graph, based on a longitudinal study of more than 400,000 people:

And yes, for vigorous activity, the curve starts to level off after about an hour. Are there no further benefits? That's what it looked like to O'Keefe et al., so they wrote a letter to Lancet making that point:

We are curious as to whether Wen and colleagues have data about long-term survival in individuals who did vigorous exercise for more than 50 min per day. Do the mortality benefits begin to erode away as the daily time spent doing vigorous physical activity increases beyond 1 h?

Wen and colleagues reply that yes, they do have data -- and it doesn't show what O'Keefe et al. hope:

By 120 min [per day], the hazard ratio for all-cause mortality was around 0·55 [which is better than it was for 60 min per day], with even better hazard ratios for cardiovascular diseases... The adverse effects of strenuous exercise for incremental efforts for more than an hour a day did not seem to outweigh the benefits. We were not able to identify an upper limit of physical activity, either moderate or vigorous, above which more harm than good will occur in terms of long-term life expectancy benefits.

This exchange took place before the recent spate of review articles about the dangers of too much exercise was published. And yet the study is still being cited as evidence that doing more than an hour a day of exercise is bad for you. As a subsequent letter to the journal from Michael Bubb of the University of Florida put it, "The interpretation of the data provided in the review by O'Keefe et al is misleading, particularly given the response of the authors of the original data."

To reiterate, I'm not flipping to the other extreme and arguing that there's no point of the diminishing returns for exercise, or even that there's no possibility of heart damage associated with extreme ultraendurance exercise. These are open and legitimate questions. But this scaremongering about relatively modest amounts of exercise in favor of "hunter-gatherer" exercise is silly. We can speculate all we want about "potential" risks and benefits, but the real-world epidemiology is crystal-clear: if you exercise for an hour a day, you're likely to live longer than if you exercise less than an hour a day.