Blood Clots in Runners

Kelly Wiebe, one of Canada’s top distance runners, had a serious health scare. He had an undiagnosed blood clot in his leg, possibly precipitated by a minor muscle injury during training, which then got infected and almost killed him. Wiebe isn’t the only top runner to get hit by a blood clot – others like Lee Troop and Lynn Jennings have also run into similar troubles. While Wiebe’s troubles stemmed from an infection, the more serious danger from certain types of blood clots is that a piece breaks off and travels to your lungs, causing a life-threatening pulmonary embolism.

I got an email from a reader asking whether athletes are at higher risk of blood clots. On the surface, the obvious answer is no, because some of the key risk factors are obesity, heart disease, and a sedentary lifestyle. But it turns out there are also some factors that work in the opposite direction and raise the risk for athletes. So I decided to look into it. The key takeaway:

The risk factors for blood clots and pulmonary embolism can be grouped into three categories: how prone your blood is to clotting; how smooth or damaged the walls of your blood vessels are; and how vigorously your blood flows. As it happens, endurance athletes are prone to all three risk factors, explains Dr. Claire Hull, a medical researcher at Swansea University in Wales.


  • Dehydration and inflammation make your blood more prone to clotting;
  • Physical trauma like muscle strains can damage blood vessel walls;
  • Low blood pressure and a low resting heart rate allow blood to pool during periods of immobility, and flow is further compromised when athletes take long flights to and from competitions.
  • That means that athletes aren’t immune from blood clots – but it doesn’t necessarily mean that they’re at higher risk than the general population (despite some of the claims you’ll find online). According to Dr. Hull, there simply isn’t any reliable data on the prevalence of blood clots at this point, so it’s impossible to draw comparisons with other groups. Still, it’s clear that we should be aware of the risks, take seriously the familiar advice to get up and move around during long flights and car rides, and know the warning signs that signal you should head to the hospital to get checked out.

Dr. Hull and her colleague Julia Harris published an excellent information sheet on athletes and blood clots in the journal Circulation that are worth checking out.


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