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For now, we don’t really have enough data to draw any conclusion about specific intensities or patterns of exercise and their link to arterial health. Still, taken together, these studies strengthen the picture that long-term endurance training is associated with more plaques but of a less dangerous type. So what message, in practical terms, should we take from this?

The accompanying editorial is by Aaron Baggish, of Massachusetts General Hospital, and Ben Levine, of the University of Texas Southwestern — both leading researchers in this area as well as sports cardiologists who are in the trenches dealing with masters athletes. They make three key points in their discussion.

The first is the old correlation-versus-causation caveat. Does endurance exercise really cause plaque buildup? There are some plausible hypotheses — that the turbulent, high-pressure blood flow through arteries during exercise contributes to plaque formation, or that hormones associated with intense exercise play a role.

But these studies don’t prove that link — and more than half the athletes in the two studies had no evidence of any calcification at all, despite their decades of hard training. So clearly training on its own isn’t enough to directly cause plaques.

So the second point Baggish and Levine raise is the potential role of unmeasured confounding variables. Do hardcore lifelong endurance athletes — or at least some of them — tend to eat poorly, without realizing the hidden consequences because their training keeps them thin? Do they overuse anti-inflammatory medications? Are they chronically stressed out? We don’t know.

The third point is the most important: the absence of data on clinical outcomes. In the average sedentary person, we know that high CAC scores are associated with an elevated risk of future cardiovascular events. And we know that prolonged endurance exercise seems to be associated with higher CAC scores in some people. But we don’t have any data linking high CAC scores in athletes with elevated risk of cardiovascular events. Both the British and Dutch studies offer convincing evidence that plaques in athletes are “different” from those in other people — so we still need to figure out what they mean in practice.

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For Baggish and Levine, who deal with lots of endurance athletes in their clinics, CAC scores simply aren’t a high priority compared to more conventional and well-understood risk factors like cholesterol levels and blood pressure (which can be managed with lifestyle changes and drugs), and exercise capacity testing (which can be managed with, well, exercise). When they see patients with high CAC scores, they don’t currently recommend reducing training — instead, they discuss the current state of knowledge about risk factors, and offer guidance on some of the other ways of lowering risk.

Related: The Worst Thing for Your Heart

That seems to me like a pretty good place to leave things. Obviously we all want better information and more certainty, and hopefully further research will get us there. But until then, it’s not clear what CAC scores really mean in endurance athletes.

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In fact, it reminds me of a spoof article in the Canadian Medical Association Journal a few years ago: “Cigarette smoking: an underused tool in high-performance endurance training.” Numerous studies show that smokers have higher lung volume and higher hemoglobin levels — factors associated with endurance performance, but also with respiratory problems.

So should runners smoke in order to get faster? Of course not: The meaning of a measurement depends on who is being measured.

This Fox News article is used by permission; it first appeared in Runner’s World. See also the author’s in-depth feature in Runner’s World from last fall.

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