The researchers found that the risk increased with more flights taken during a shorter period of time. It also increased with the length of flights. The risk was particularly high for those under age 30, women who used oral contraceptives, and individuals who were particularly short, tall, or overweight, Rosendaal said.
In addition, the risk of thromboses was highest in the first two weeks after the travel and after eight weeks post-travel, according to the report in the September issue of the online journal, PLoS Medicine.
Rosendaal noted that although the risk to individuals is very small, some people are taking precautions that he called "over the top."
"People should lighten up," he said, referring specifically to people who take aspirin before flying.
There is no evidence that blood-thinning aspirin prevents venous thrombosis, but it can cause abdominal bleeding, Rosendaal cautioned. "People shouldn't take aspirin for this -- it doesn't work," he said.
There is really no known preventive measure for economy class syndrome, Rosendaal said. The best advice is to move your legs and feet. There is no proof that elastic stockings and leg bands work, either, he noted.
Taking the blood thinner heparin will prevent venous thrombosis, too. But it can trigger bleeding and that risk outweighs its small benefit in preventing an in-flight venous thrombosis, Rosendaal said.
"The only thing that makes sense is to move your feet," he said.
One expert believes the risk of venous thrombosis from air travel is tiny compared with more common causes.
"This large, rigorously-conducted study was carried out by one of the world's top clinical research groups in venous thromboembolism," s
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