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Deep Vein Thrombosis Health Center

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No Link Shown Between Long-Distance Flights, Blood Clots


"These results do not lend support to the widely accepted assumption that long traveling time is a risk factor for [DVT]," writes study author Roderik Kraaijenhagen. "Even for journeys lasting more than five hours, no association was apparent."

Kim tells WebMD that because this condition is relatively rare and difficult to diagnose, a study involving 700 people may not have been large enough to disprove a connection between blood clot formation and long flights.

Clifford C. Dacso, MD, MPH, a professor of medicine and chief of general medicine at Baylor College of Medicine in Houston, agrees that the study may be too small to be significant. "But I don't even think it is relevant. It probably does occur, but it may not. Even if it doesn't, the remedy we know is harmless. I think it is pretty nontoxic to tell people to get up every hour and walk around, flex their calf muscles 10 or 20 times an hour," says Dacso.

Patricia M. Young, MD, medical director of the International Travel Clinic at the Medical College of Wisconsin in Milwaukee, tells WebMD it is unclear whether the British woman who died had medical problems or previous injuries that might have caused her fatal blood clot. "Other risk factors for DVT are major surgery in recent weeks, certain types of cancer, heart failure, and varicose veins," says Young.

She says she agrees with the Lancet study conclusion that there is probably no association between flying itself and the development of clots.

"Most travelers are healthy enough that they will be moving around somewhat, which stimulates blood flow by causing contracting muscles to pump the blood onward," says Young, who was not involved in the study but reviewed it for WebMD. "The travel itself is not necessarily the cause of DVT, but the immobilization that many passengers undergo during a flight, perhaps combined with tight fitting clothes that impede blood flow, can increase risk of stagnating blood in lower leg veins."

Young suggests taking an aspirin the day of travel to help thin the blood. "I would continue to encourage travelers to wear comfortable clothing for travel, walk about frequently, clench their toes or rotate their ankles to stimulate blood flow, as well as stay hydrated, so the blood is thinner during their long periods of sitting," she says. "Airlines may need to lead the way in educating people about immobilization risks and perhaps return to more leg room so that passengers can move around easier."

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