Long Flights Double Risk of Blood Clots

Dec. 8, 2003 -- Rather than bringing a book on long airplane trips, you might want to bring your walking shoes.

New research shows that flights over eight hours long can double the risk of potentially dangerous blood clots during or shortly after flight. But you can substantially reduce your risk of these complications by knowing your risk and simply getting up and stretching in flight.

Three studies in the Dec. 8/22 issue of The Archives of Internal Medicine shed new light on the link between air travel and the much-hyped "economy class syndrome."

Researchers say air travel mildly increases the risk of blood clots forming in the veins, known as venous thromboembolism (VTE), but the risk is greatest in older people, those who are overweight, or have other genetic and environmental risk factors.

For example, people who lack certain proteins that prevent or break up clots or women who take birth control pills may be 14 to 16 times more likely to develop these blood clots during or shortly after air travel.

Assessing the Risk of Economy Class Syndrome

In the first study, Italian researchers compared 210 people who suffered VTE with 210 similar healthy people.

The study showed that air travel was reported in the preceding month by 31 of those who had suffered the blood clots compared with 16 of the healthy people.

More than 100 of those who had VTE also had genetic factors that predisposed them to blood clots compared with only 26 of the healthy people. Use of birth control pills was also much more common among women with VTE (61% vs. 27% of those of reproductive age).

Researchers say that air travel alone was only a minor risk factor for VTE, but the addition of either clotting risk factors or use of birth control pills increased the risk of blood clots by 16-fold and 14-fold, respectively.

In the second study, German researchers used ultrasound to detect blood clots in 964 passengers who had just returned from long-haul fights and more than 1,200 nontraveling people.

Researchers found blood clots in 2.8% of the travelers compared with 1% of the nontravelers. Most of these did not produce any symptoms and were found in the calf muscle veins.

The study showed flights of eight hours or longer doubled the risk of developing these blood clots in the calf. Most of the people who suffered from clots had well-known risk factors, such as being over 50 years old, overweight, having a personal or family history of the condition, or recent surgery.

Since most of the clots were isolated in the lower leg, researchers say the use of compression stockings may reduce this risk but more study is needed to prove this.

Too Much Sitting to Blame

In an editorial that accompanies the studies, James E. Dalen, MD, MPH, an editor at the journal, says that too much sitting, not too much flying in cheap seats, is largely to blame for economy class syndrome.

"Since seating in economy class is more cramped that in first class, passengers in economy class are more likely to remained seated throughout the flight," writes Dalen. "The term economy class syndrome seems appropriate. However, it should be noted that the reason that most of the reported cases of flight-related VTE have occurred in patients traveling in economy class is that most passengers fly in economy class!

"All of those who are at increased risk should avoid prolonged sitting by getting up and walking frequently during long trips by airplane, car, or train," he writes.