Is Running Too Much Bad for You?

It's been all over the news this week: Too much running will kill you. Fast running will kill you. Running too much has the same health consequences as being sedentary.

Having read so many studies about the benefits of running, this didn't sound right to me. So I went to Runner's World to see what they had to say.

They had quite a bit to say. In "The (Supposed) Dangers of Running Too Much," Alex Hutchinson reveals that it's an old study originally published in 2012 and published again that makes sensational claims on faulty statistical sample sizes. Says Hutchinson, "...the study is worth paying attention to, and we should take the results seriously if and when the data reaches any reasonable threshold of statistical significance. At this point, though, they're nowhere near that threshold."

He goes on to say:
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.

Hutchinson shows the raw data, and you can see just how few people the authors researched and how difficult it would seem to be to see patterns in the data.
Does your risk really go up if you run more than 2.5 hours, but then go down again if you run more than four hours? Of course not. These are not real patterns, because we're talking about one, two, three, or at most five or six deaths. No matter how interesting or important the question is, you can't torture these numbers enough to force them to reveal the answers. They're simply not there.
Hutchinson points out other statistical challenges with the data including age and gender. 

In the article "How to Interpret the Latest 'Excessive Running' News Reports," Scott Douglas states that, "An editorial in the Journal of the American College of Cardiology makes the same point" as Hutchinson does above. Douglas goes on to say:
In addition, the study's findings have only to do with mortality during the study period. Many mainstream articles, however, have broadened the conclusion to suggest more ambitious running is of equal health benefit to being sedentary. Such claims ignore the wealth of data that show that, while many of the health benefits of running accrue at modest amounts of mileage, in many studies, higher-mileage runners gain more benefits.
The media loves sensational headlines, but I'm going with Runner's World on this one when they conclude that "We at Runner's World don't think this one study is reason to change your approach to or appreciation of running."