What's the Relation Between Flying and Blood Clots?

Life-threatening blood clots and flying have been linked for more than 50 years, but a new study of business travelers confirms the risk, particularly for those who take long flights or fly frequently. Immobility is considered a major factor behind the condition, called deep vein thrombosis.

But while it is often referred to as “economy-class syndrome” because of the cramped seating there, D.V.T. also occurs among those who fly in business class and first class, the researchers found.

People who fly four hours or more, the study found, have three times the risk of developing clots compared with periods when they did not travel.

D.V.T. occurs when a blood clot forms within the large deep veins of the body, usually in the leg. If untreated, part of the clot may break off and travel to the lungs, where it can cause a pulmonary embolism, a potentially fatal condition.

Frits R. Rosendaal and Suzanne C. Cannegieter of Leiden University Medical Center in the Netherlands, the study’s lead researchers, tracked almost 9,000 employees of large international companies and organizations over a four- or five-year period, in what they call the most comprehensive study of its kind to date. The results were published this fall in the online journal PLoS Medicine; preliminary findings were reported in late June by the World Health Organization.

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