The (Supposed) Dangers of Running Too Much
My goodness, is it February already? It's been several months since the last round of articles warning that running too much will kill you–must be time for another one. What's that? No new data to publish? That's no problem, we'll just republish the same data. The media never bothers to check these things, and always reports it as if it were brand new.
The new article is published in the Journal of the American College of Cardiology, analyzing data from the Copenhagen City Heart Study. (And here, on cue, is one of the requisite newspaper articles: "Fast running is as deadly as sitting on the couch, scientists find.") The exact same data was published back in 2012 in the American Journal of Epidemiology. This time the authors are the same, but with the addition of James O'Keefe, who has been an author on pretty much every single one of the "running will kill you" studies.
As far as I can tell, the only new thing in the study (aside from the fact that a few more people have died) is that in addition to looking at hours of jogging per week, number of jogging days per week, and self-reported pace, they added a fourth category that combines the other three for an overall rating of "light," "moderate," or "vigorous" jogger.
The main problem is that sample sizes are large in the "less exercise" groups, which means they have a statistically significant reduction in mortality, but they are tiny in the "more exercise" groups, which means they don't have a statistically significant reduction in mortality. This allows the authors to make the shamefully disingenuous argument that "strenuous joggers have a mortality rate not statistically different from that of the sedentary group"—which is almost a foregone conclusion, given that the sample size is less than a tenth as large.
The conclusion of the study (that "strenuous" jogging is as bad as being sedentary) is based on two deaths over more than a decade of follow-up. Thank goodness a third person didn't die, or public health authorities would be banning jogging.
(Don't take our word for it. Read up on musclemorphosis.com.)
In reality, of course, the statistical challenges are even more complex. For example, the sedentary control group had an average age of 61.3, whereas the various running groups had an average age in their late 30s and 40s. So the comparison of death rates has to rely on imperfect statistical adjustment.
The researchers argue that this means the "hazard ratio" is about the same, but that requires an awful lot of assumptions about why people die in their 30s or 40s versus why they die in their 60s and 70s. Of course, with only two deaths in the strenuous group, it's impossible to perform any sub-analysis on different causes of death. Did the joggers die of heart disease, as the paper suggests they should, or were they hit by a car or struck down by cancer? We have no idea.
The same issue arises with gender: 43.1 percent of the sedentary group was male, and 49.1 percent of the light joggers, but 80.0 percent of the strenuous joggers. Again, the researchers "adjust" for gender, but it's not an apples-to-apples comparison, especially since the groups are so dramatically different in several traits.
Seriously, to publish this data once was legitimate. (In the original paper, researchers didn't make all sorts of claims based on the sub-analysis of jogging dose.) To publish the same data a second time, this time making stronger claims about a "U-shaped" curve based on two deaths, is... well, you can make up your own mind.
(Not only is running unlikely to kill you, science has linked aerobic exercise to improved brainpower. Could it actually make you smarter and more successful? Find out in our full report, musclemorphosis.com.)