XC skiing and arthritis

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To be perfectly honest, I wasn’t thrilled to see the results of this study (tweeted by Amby Burfoot). But data is data*, and if you report the good news you can’t ignore the bad. Swedish researchers did a very cool analysis of 54,000 men and women who competed in the famous 90 km Vasaloppet classic-style nordic ski race between 1989 and 1998 (full text available here). What’s fascinating is that Sweden keeps meticulous records of all its citizens, including all the in-patient health care they receive, linked to a 10-digit identification number. So the researchers were able to link the names and finishing times of all the racers with their health records, census data (to check confounders like education, occupation and income), death records and emigration records.

The basic question they looked at was: does exercise (as represented by the number of times subjects raced the Vasaloppet in the 10-year window, and their fastest finish) correlate with severe osteoarthritis later in life (as indicated with having a knee or hip replacement due to arthritis). The answer, unfortunately, was yes. For example, those who completed five or more races and had a fast finish time were 2.73 times more likely to need a joint replacement in the following ~10 years than those who participated only once and had a slow finish time.

The results contrast with a string of recent studies that found that, if anything, longtime runners are less likely to develop arthritis than non-runners. So there are a few questions here. Does the skiing motion have some unique effects on joints, causing more stress and cartilage damage? Or is it more a question of degree: “moderate” exercise is good for the joints, but 90 km ski races (which took between four and 13 hours to finish) are a bit too extreme? I don’t know, but I suspect the latter is a factor.

One point worth noting. Compared to similar studies of the general population, the skiers as a group had exactly the same risk for knee replacement, and a slightly higher risk of hip replacement. That suggests that, while the elite athletes at the front of the pack were worse off than the general population, the “casual” exercisers toward the back of the pack were in fact better off than the general population (though “casual” isn’t really the right term for someone doing a 90 km ski race).

And a last point: the same group has made several other studies of the characteristics of Vasaloppet finishers. Even if their knees get creaky, they do live longer than their sedentary peers; and the more races they do, the longer they live. So that’s something, I guess!

[* I know, “data” is supposed to be plural. Hopefully people will overlook this transgression… :)]