Long Flights Double Risk of Blood Clots
Economy Class Syndrome Largely Limited to Older, Overweight People
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
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,
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
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.