Air travel may be linked to blood clots in Marathon runners

A recent study has found that Marathon runners who travel by air to the race may end up with higher blood levels of molecules that have been linked to blood clots. Blood clots usually form in veins, and can be dangerous if they break off and block blood supply to the lungs or heart. Researchers said that it didn't mean flying is actually likely to trigger a blood clot in endurance athletes or that air travel should be avoided. But it does suggest a possible explanation for the rare but mysterious reports of clots in otherwise healthy marathoners who flew to a race. "It seems that the two activities could have a compounding effect when they are carried out back-to-back," said Beth Parker at Hartford Hospital in Connecticut, who led the research.

In the study, published in the American Journal of Cardiology, Parker and her colleagues took blood samples from 41 healthy non-smokers who participated in the 2010 Boston Marathon.
Twenty-three of them lived more than a four-hour plane flight away, while 18 participants -- the comparison group -- lived within a two-hour drive of Boston. The researchers collected blood after the runners landed in Boston, immediately after the marathon, and again when the participants were back home the next day. After returning home, six people in the air travel group had elevated levels of a substance called D-dimer, which has been used as a sign of possible blood clots. By contrast, none of those who lived close to Boston did.

Air travel is known to double or triple the risk blood clots in the veins of the legs, called deep vein thrombosis, according to Parker. And endurance exercise, such as marathon running, may also raise the number of blood molecules that aid clotting. What the elevated D-dimer levels meant is unclear. None of the athletes showed actual symptoms of deep vein thrombosis, such as leg pain or swelling, shortness of breath or rapid heart rate. The researchers also found that older athletes had significantly higher levels of an inflammatory blood compound that could be associated with heart attack risk, regardless of whether they flew to the marathon or not.

Parker said that while the research suggests marathon running and air travel to get to marathons could contribute to a slightly increased risk of blood clots or other cardiovascular events, the benefits of endurance running far outweigh the small risks for most people.

Simple precautions such as staying hydrated, wearing loose clothes, not crossing your legs for long periods of time, walking around the cabin every one to two hours and wearing compression stockings  can reduce the risk of blood clots while flying.