Up to one in 100 long-haul fliers could develop blood clots, and wearing compression stockings, taking aspirin and traveling business class may not help, a study showed on Friday.

New Zealand researchers tested almost 900 passengers who took long-haul flights over a six-week period. The subjects traveled for at least 10 hours and each flew an average of 39 hours.

They discovered nine cases -- four of pulmonary embolism and five of deep vein thrombosis (DVT), which involves the formation of blood clots which can cause death if they invade the lungs or brain.

Seventeen percent of the passengers in the study by the Medical Research Institute of New Zealand wore compression stockings to aid circulation. Thirty-one percent took aspirin to thin the blood and reduce the risk of thrombosis.

The team, whose report was carried in The Lancet medical journal, said all air travelers were at risk, not just those in economy class.

"As a result, our findings lend support to the recommendation that the term 'economy class syndrome' should be avoided with the disorder renamed 'traveler's thrombosis.'"

The New Zealand team concluded that their findings may err on the side of conservative estimates.

During recent court action, victims have blamed cramped aircraft cabins for their blood clots and argued that airlines have known of the risks for years but failed to warn people.

But a British court agreed with the airlines, which claimed that DVT was not an accident under the 1929 Warsaw Convention that governs international air travel.

DVT made international headlines and airlines came under pressure to do more to prevent the condition after a 28-year-old British woman died from the condition about three years ago after a 20 hour flight from Australia to London.

(Reuters)