I just want to add a few quick thoughts on a study that Amby Burfoot reported on recently. It's a new analysis from Paul Williams' National Runners' Health Study, published in Medicine & Science in Sports & Exercise, that compares arthritis rates in about 90,000 runners and walkers. Amby's report is very thorough; if you haven't read it already, you should.
In brief, the study found that that runners are about half as likely as walkers to develop osteoarthritis or need a hip replacement. The biggest reductions occured for those running between 7 and 21 miles per week (Amby's post has more details). Most of the relationship seems to be explained by BMI: runners weigh less than walkers, who in turn weigh less than people who don't exercise at all. Less weight reduces arthritis risk.
What annoys me is that this study will surprise many people (and worse, be ignored by many more). It shouldn't be a surprise -- whenever people have followed runners prospectively to monitor arthritis rates, they've been better off than non-runners. (For example, here's an article I wrote almost five years ago about one such study.) On the other hand, it's pretty well established that sports like soccer and hockey do carry elevated risks of arthritis down the road. And when you dig into the data, you find that this elevated risk is attributable to those who suffer serious injuries during their playing career -- which definitely is an arthritis risk factor.
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And yet people -- doctors, researchers, experts -- continue to view running as the prime example of an activity that raises your risk of arthritis. Here's an example that annoyed me when I read it a few months ago. It's a press release about a study that monitored 205 patients for four years to check progression of cartilege degeneration, and found that there was a "sweet spot" of moderate activity levels -- too little or too much activity was associated with greater cartilage degeneration.
Now, this is an interesting finding. But in the press release, they repeatedly single out running as a culprit. E.g.
According to the results of the study, participating frequently in high-impact activities, such as running, appears associated with more degenerated cartilage and potentially a higher risk for development of osteoarthritis.
If you go to the conference abstract, on the other hand, you find that they assessed physical activity using something called the "Physical Activity Scale for the Elderly" questionnaire, a tool that makes no attempt to separate running from other types of "strenuous" activity like swimming, cycling, cross-country skiing and downhill skiing (an activity with obvious risks for the type of acute knee injury that we know very well raises arthritis risk).
This is just sloppy. And it's how the assumption that running causes arthritis gets perpetuated -- when researchers find one thing and report something else.
