Blog | Monday, March 9, 2015

Is running bad for you? How the media is easily confused


At dinner earlier this week, some friends told me that running hard had the same mortality as being sedentary. Here is one example of articles written about the study – Slow Runners Come Out Ahead

As it turned out, and as expected, joggers consistently tended to live longer than people who did not exercise.

But when the researchers closely parsed the data about how much and how intensely people jogged, some surprises emerged.

The ideal amount of jogging for prolonged life, this nuanced analysis showed, was between 1 hour and 2.4 hours each week. And the ideal pace was slow. (The researchers did not specify exact paces in their study, using instead the broad categories of slow, average and fast, based on the volunteers' self-reported usual pace.)

Plodding joggers tended to live longer than those who ran faster. In fact, the people who jogged most often and at the fastest pace, who were, in effect, runners rather than joggers, did not enjoy much benefit in terms of mortality. In fact, their lifespans tended to be about the same as those who did not exercise at all.

But this study actually does not prove that. Here is Alex Hutchinson's article about the study: The (Supposed) Dangers of Running Too Much

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 first article is in the New York Times; the second, Runners World. But the next article is also in the New York Times, No, More Running Probably Isn't Bad for You

In fact, the main thing the study shows is that small samples yield unreliable estimates that cannot be reliably discerned from the effects of chance. And the main thing the reaction shows is that perhaps we are all a bit too quick to believe medical studies that tell us what we want to hear.

The study doesn't change what the weight of the evidence shows: Most Americans need to worry about exercising too little, not too much, and it's not clear that any substantial number of people are harming their health by running too much.

Too often reporters describe medical articles without carefully examining them. Most medical articles either advance or knowledge in a small way, or provide an interesting hypothesis that needs further study.

We have a responsibility to question both scientific articles and newspaper articles.

db is the nickname for Robert M. Centor, MD, FACP. db stands both for Dr. Bob and da boss. He is an academic general internist at the University of Alabama School of Medicine, and is the Regional Associate Dean for the Huntsville Regional Medical Campus of UASOM. He still makes inpatient rounds over 100 days each year. This post originally appeared at his blog, db's Medical Rants.