Heart health, exercise, and misleading correlations
Just noticed a great post on Amby Burfoot’s Peak Performance blog where he interviews Paul Thompson, the Hartford Hospital cardiologist who’s the go-to guy for questions about exercise and heart health. It’s a fantastic interview, very wide-ranging, with Thompson sharing his thoughts, hunches and beliefs about a bunch of the current controversies in this area.
One part that caught my attention in particular was a question about a recent German study that found a high prevalence of hardened arteries among marathon runners (I blogged about it here). Thompson was a co-author on the study, and he shared a frank assessment of some of the study’s strengths and weaknesses:
[H]is marathon group includes a number of former smokers and others who might have been quite unhealthy before they began running…
The key issue with Mohlenkamp’s runners is that their cardiac risk scores are compared using their present cholesterol, blood pressure, and other health numbers. They might have had terrible numbers before they started running, so when their coronary calcium is compared with folks who are not athletes, but had good risk numbers all their lives, it looks like the runners had more calcium, ie, more atherosclerosis than predicted by their risk factors… Many of the runners “got religion” when they turned 40 or so.
This is a classic illustration of why a single study, or even a single group of studies, can so easily point us in the wrong direction. On the surface, it looks simple: take a bunch of marathoners, compare them to controls, and presto — marathoners have worse arteries. But it’s easy to be led astray by underlying factors (not to mention, as Thompson points out, that the hard, stable arterial plaques found in the runners may actually be a good thing, as opposed to soft, unstable plaques that are easily dislodged).
Anyway, it’s an interesting read, and Burfoot does a great job “pinning Thompson to the mat” to get his (well-informed) opinions and best guesses on a bunch of topics.