Travelers’ clot risk, already small, can be made even smaller

Special to The Times

Long-HAUL airplane flights increase the risk of dangerous blood clots and accumulation of fluid in the lower leg, new studies show. But overall the risk is modest, one researcher says, and no cause for alarm.

Still, fliers with a history of blood clots or who are overweight or taking birth control pills are at higher risk than others, both during and after air travel, the new research suggests. These passengers might consider preventive measures, such as wearing compression stockings during and after a long-haul flight.

Dr. Thomas Schwarz of University Hospital in Dresden, Germany, who led a study of blood clots and air travel that was published in the December issue of Archives of Internal Medicine, says preventive measures can reduce the risks. “Videotapes on how to practice stretching exercises should be mandatory on all airlines on long-haul flights,” Schwarz says.

The scientific community has long debated the link between long-haul air travel, generally defined as flights of eight hours or more, and blood clots. In 2001, World Health Organization officials concluded that the link was probably small and would mainly affect travelers who had additional risk factors, such as a history of blood clot problems.


The most recent studies seem to echo that finding. Schwarz’s team evaluated 964 passengers returning from long-haul flights and 1,213 nontraveling control subjects. He found that long-haul flights doubled the risk for a condition called “calf muscle venous thrombosis,” a clot isolated in the muscle in that part of the leg. That, in turn, increased the risk for deep venous thrombosis, or DVT, in which blood clots form in the deep veins, including those in the legs, and can be fatal.

DVT has been dubbed “economy-class syndrome,” because experts think sitting in cramped seats with low cabin pressure may contribute to the problem.

Schwarz’s study also found that those who had problems with clots tended to be overweight and older than those who did not. Those in the clot group averaged 66 years old, those in the healthy group, 63.

Of the 20 found to have calf muscle venous thrombosis, 15 had elevated body mass indexes, or BMI, a measure of height to weight. (A person who is 5 feet, 6 inches who weighs 167 has a BMI of 27.) A BMI of 25 or above is considered overweight; the mean BMI of these 15 travelers with elevated BMI was 26.8.

In a second study, also published in December’s Archives, Italian researchers evaluated 210 patients with blood clots and compared them with 210 healthy subjects. In the previous month, 15% of those with clots had flown in an airplane.

In a third Archives study, researchers evaluated blood clots in the lungs of passengers arriving at Madrid’s Barajas airport and found 16 cases in six years. All who had the clots had been on flights of six or more hours.

Fluid accumulation in the legs, a sign that blood is pooling rather than circulating, is common in air travelers, even those not considered at high risk for clotting problems, according to a study in the December Journal of Travel Medicine.

Among preventive measures are wearing pressure stockings, available at drugstores without prescription and through travel supply stores online, during and after the flight; walking around the cabin when possible; and in-flight exercises.


In-flight exercises are posted on the American Council on Exercise website, .cfm?ItemID=273.

Healthy Traveler appears every other week. Kathleen Doheny can be reached at