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The risk of blood clots through long-distance traveling

Travel by Air, Ground Linked to a Tripled Risk of Blood Clots

By Nicole Ostrow

July 6 (Bloomberg) -- Traveling long distances by plane, bus, car or train may nearly triple a person’s risk of blood clots in leg veins and lungs, a review of previous studies found.

For each two-hour increase in travel time, the risk of developing a clot, known as venous thromboembolism, increased 18 percent, according to research published online today in the Annals of Internal Medicine. For air travelers, the risk rose 26 percent for every two-hour increase in time spent on the plane, research showed.

The review, which analyzed 14 previous studies including 4,055 cases, is the largest and most comprehensive to find that travel increases the risk of blood clots, lead author Divay Chandra said. More than 200,000 new cases of venous thromboembolism occur each year in the U.S. with a 30 percent risk of dying within 30 days, according to the American Heart Association.

“People who travel, particularly if they travel long distances, they should be aware of these symptoms,” said Chandra, a fellow in the division of pulmonary, allergy and critical care medicine at the University of Pittsburgh Medical Center, in a July 3 telephone interview. “They should not be ignored.”

Symptoms of a blood clot include swelling in the arms or legs, skin redness, soreness or pain in the arms and legs or a warm spot on the legs, according to the U.S. Department of Health and Human Services.

Drink Water, Walk

All travelers should drink water and walk occasionally while en route to prevent these clots, Chandra said.

Previous studies have reported conflicting results on whether long-distance travel was linked to blood clots. To resolve the question, Chandra and colleagues at Harvard Medical School reviewed 14 studies that looked at the rate of blood clots in travelers compared with nontravelers.

Pooling the results from all 14, the researchers found double the number of blood clots among the travelers. Six of the studies didn’t use the best study design, according to Chandra, because the comparison group of nontravelers had already been previously selected for testing to see if they had clots.

Excluding results of those six, they found the risk of developing a blood clot about tripled for travelers. The researchers also saw the risk was higher for those who traveled by plane compared with those who took ground transportation, but the increase wasn’t statistically significant, Chandra said.

4,600 Flights

The analysis drew its conclusions by reviewing the results of the 14 studies and reported relative risks, rather than numbers of cases. To illustrate how high the odds may be for any one traveler, the article cited a previous study estimating one blood-clot case occurred for every 4,600 airline flights.

Blood clots that form in the legs may be fatal if they break loose and move to other parts of the body, including the lungs, according to the NIH. Twenty percent of those with a lung clot, or pulmonary embolism, suffer sudden death, according to the American Heart Association.

Doctors are still studying exactly why traveling may cause blood clots, and some suspect that lack of mobility may discourage blood flow and enable clots to form.

Future studies are needed to show if travelers can lower their risks by drinking fluids, walking occasionally while en route or taking other measures taken before they embark, Chandra said.

People who are considered high risk for blood clots -- those with cancer, smokers and those who have had clots before - - should talk to doctors and may need to take blood thinners before making a long trip, Chandra said.

To contact the reporter on this story: Nicole Ostrow in New York at nostrow1@bloomberg.net.
Last Updated: July 6, 2009 17:00 EDT

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