STOCKINGS, aspirin and even travelling business class do not protect long-distance air travellers from developing deep vein thrombosis, researchers have found.

In one of the largest studies yet published into DVT, researchers discovered that around three to four passengers on every jumbo jet are likely to develop the disease.

Although most will never develop symptoms some will die if the embolism reaches their lungs. 30,000 people die each year in Britain from pulmonary embolisms. Doctors at King’s College London estimate that about 1,000 of these are due to flying.

The study, published today in The Lancet, is certain to be one of the first to be investigated by the Civil Aviation Authority’s new aviation health unit. Established at the start of this month, its remit is to investigate all the evidence into flying-aquired DVT and to make recommendations to the Departments of Health and Transport.

Researchers in New Zealand, led by Richard Beasley, from the Medical Research Institute, studied 878 people who took long-haul flights over a six-week period.

All participants travelled for at least ten hours, each flying an average of 39 hours. Individual flights lasted at least four hours.

Seventeen per cent of the passengers wore compression stockings and 31 per cent took aspirin to reduce the risk of thrombosis.

The researchers identified four cases of pulmonary embolism and five of DVT, amounting to 1 per cent of the total. Six patients with blood clots had pre-existing clinical factors, two only travelled in business class, five took aspirin, and four wore compression stockings.

“Our findings lend support to the recommendation that the term economy-class syndrome should be avoided,” the authors wrote.

However, all those who took part in the study were classified as having a low to moderate risk of DVT. High-risk patients were deliberately excluded.

“The true frequency of air travel-related venous thromboembolism has been difficult to ascertain,” the study said. “Researchers suggest that the prevalence of severe pulmonary embolism arising after long-distance travel could be as low as 4.8 per million. This value represents an under-estimation of the true prevalence.”

The authors said that their study suggested the figure was much higher but not as large as the 10 per cent estimate in another recent research project.

“Our findings suggest that venous thromboembolism is a potentially important health problem to many long- distance air travellers, including those without recognised risk factors,” Professor Beasley said.

“They question the previous assumption that most individuals who have air travel-related venous thromboembolism have pre-existing risk factors that are identifiable before travel.

“The role of traditional risk factors and prophylactic measures in needs further investigation.”

Ander Cohen, a leading expert on DVT and consultant vascular surgeon at King’s College London, welcomed the findings.

“This is a useful and important study,” he said. “It backs up our research which shows people get a false sense of security out of taking aspirin when in reality it will not protect you against DVT.

“Equally the findings on stockings are very interesting and are important as part of research into this field.”

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