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Deep Vein Thrombosis Health Center

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In-Flight Blood Clots: Theory Grounded

Low Oxygen on Long Flights Doesn't Seem to Cause Clots, Study Shows

Checking for Clotting Risk continued...

The study included 12 women who were taking oral contraceptives (which raise clotting risk) and another group of 12 people aged 50 and older. Those groups' test results didn't show higher clotting risk, but with such few participants, it's hard to be sure of that finding, the researchers note.

It's not clear if the results apply to people with other health conditions. The study was funded in part by the U.K.'s Department for Transport.

Another recent study, done in the Netherlands, showed that low oxygen levels on long flights might increase clotting risk in some fliers.

Surprising Finding

The finding that low oxygen and prolonged sitting didn't raise clotting risk was "surprising," writes editorialist Peter Bartsch, MD. He works in Germany at the Universitatsklinikum Heidelberg and wasn't involved in Toff's study.

The Dutch and British studies weren't exactly like a real flight, Bartsch notes, noting the alcohol ban and hourly activity allowed in the experiment.

Bartsch writes that "the small number of older participants and individuals taking oral contraceptives preclude drawing reliable conclusions about these groups." He also asks if lower oxygen levels might interact with other risk factors, such as advanced age and a history of DVT.

The results might not apply to clotting risk in mountain climbers at high altitudes, Bartsch also notes.

Avoiding in-Flight Clots

In a University of Leicester news release, Toff commented on his study.

"Although we found no evidence that the low pressure and low oxygen activate blood clotting, we know from many other studies that prolonged sitting, such as during long journeys by air, road or rail, does increase the risk of deep vein thrombosis (DVT). That link is quite clearly established," Toff says.

"The overall risk of thrombosis [clotting] after a long-haul flight is estimated to be about 1 in 2,000," he continues. "For people with known risk factors, the risk may be higher but for those without other risk factors it is likely to be very low and should be kept in perspective."

Toff recommends taking "sensible precautions" on long flights, such as regularly doing leg exercises, getting up and walking around the plane's cabin from time to time, wearing special compression stockings, and (if recommended by a doctor) taking anticlotting drugs.

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