Travel more than doubles risk of blood clots: study

WASHINGTON (Reuters) - People who travel have nearly triple the normal risk of developing a dangerous blood clot, with a measurable increase for every two hours spent sitting in a car or wedged into an airline seat, researchers reported on Monday.

They said the risk is serious enough to merit research into better ways to keep travelers healthy, although not severe enough to justify giving airline passengers anti-clotting drugs.

Dr. Divay Chandra and colleagues at Harvard University in Boston looked specifically at venous thromboembolism -- the development of a blood clot in a vein, usually in the legs.

Blood clots can also cause strokes and heart attacks when they form in arteries but VTEs can cause local damage or travel to the lung and kill.

Chandra's team did what is called a meta-analysis, pooling the results of many different studies to see what they found collectively.

They found 14 studies involving 4,000 patients that met their criteria for quality.

"Our findings demonstrate for the first time a clear association between travel and VTE," they wrote in their report, published in the Annals of Internal Medicine.

Women who are pregnant or take birth control pills and the obese have an especially high risk, they found.

The absolute risk is one case in every 4,600 airline trips, they said. They noted that some studies have shown no risk of blood clots but said the way those studies were done could be questioned.