A couple of weeks ago, many mass media outlets rushed to report that “Too much running linked to shorter lifespans” or “Walk away from excess running, study says.” Supposedly, if you run more than 20 miles a week, the effect on your heart is the same as if you were completely sedentary, according to this study, which, like an earlier study, claims that 15-20 miles per week is the magic zone. What’s going on?
* For a long and detailed critique of the study, check out Alex Hutchinson’s essay-length post. Among other things, he points out that the study in question didn’t actually track lifespan against running mileage. Instead, it’s an attempt to use a web-based questionnaire to zero out possible confounding explanations for the supposed U-shaped “more than 20 miles a week is worse than 15-20 miles a week” result found in the earlier study. The new study concludes that assuming the earlier finding is correct, it can’t be explained by cardiac risk factors or pain reliever use.
* Here’s the abstract of the new study, and the key conclusion:
Decreased longevity in runners averaging >20 miles/week vs those who run lower average weekly mileage could not be explained by higher prevalence of CAD risk factors or differences in the primary preventative use of daily aspirin. Also, we found that NSAID use was more common in runners reporting lower average weekly mileage. The underlying cause of the observed U-shaped relationship between training mileage and longevity remains unclear.
Hmm . . . that sounds quite a bit less definitive than what the media has been reporting. It’s not that running more than 20 miles a week does lead to decreased longevity. It’s that, given that past (flawed – TY) studies have seemingly shown such a linkage, can the linkage be explained by cardiac risk factors or use of pain relievers, for which the self-reported answer is no.
* On the “more than 20 miles a week is worse for you than 15-20 miles a week” study, check out what I wrote last year (including links to more detailed analyses by Hutchinson and others).
* If there is a link between “running too much” and decreased longevity, this suggestion (hint: running is not a license to eat junk food all the time) makes as much intuitive sense as anything else. It’s also why people who take up marathon training sometimes gain weight, seemingly paradoxically.
* Upshot: I’m neither a doctor nor a research scientist, so I can’t absolutely dismiss this new study. But I do think that Hutchinson is right to read the abstract carefully and to see what it is saying, and what it is not saying. On a macro level, however, the bigger question mark that these studies raise is, is there something peculiar about running, or is all endurance cardio going to lead to the same seeming correlation?