Studies link long air travel and blood clots

Flights lasting more than four hours about double a traveler’s risk of life-threatening blood clots, World Health Organization studies found.

The clots, called venous thromboembolism, can form in the legs and can be fatal when they move into a person’s lungs. The risk of VTE also applies to car, bus and train travel, where passengers are seated for long periods, the Geneva-based agency said in an e-mail statement Friday.

More than 600,000 people in the U.S. have a pulmonary embolism every year and more than 60,000 of them die, according to the National Institutes of Health. The disorder is one of the most common causes of death in bed-bound patients in the hospital. Childbirth and the use of drugs including estrogen and birth-control pills have also been linked to clots.

“There is a clear need for travelers to be given appropriate information regarding the risks and for further studies to identify effective preventive measures,” the WHO said.

The conclusions were the result of the WHO Research Into Global Hazards of Travel (or WRIGHT) project aimed at confirming previous studies linking VTE and air travel. The project also sought to determine the extent of the risk.

The latest studies found the absolute risk of a healthy individual developing such a clot on a flight lasting more than four hours was 1 in 6,000. The studies looked at various groups, including Dutch commercial pilots, employees of international organizations and carriers of frequent flier cards.

A connection between air travel and VTE was first detected in 1954. The condition can cause medical problems ranging from pulmonary embolism, or clots in the lungs, and deep vein thrombosis to stroke.

VTE is often dubbed “economy class syndrome” after health officials recognized a link to airplane passengers on long flights, particularly in the back of the plane where leg room and seating are cramped, according to the American Heart Assn. . Passengers in business and first class also may be susceptible to clots.