Air travellers three times more likely to develop thrombosis

• James Randerson, science correspondent
• Guardian Unlimited
• Tuesday September 25 2007

People who fly are more than three times more likely to develop deep vein thrombosis, according to a study of regular travellers. Researchers, funded by the government and the EU, also found that travellers who are obese or particularly short or tall, women using the pill, and under-30s were most at risk. They said airlines should create more adjustable seats with more leg room for the tallest people to prevent DVT.

The study, which followed nearly 9,000 business people for five years, concludes that on average the condition occurs once in every 4,656 individual journeys. "It clearly shows this could be prevented if seats were adjustable or there was more space," said Suzanne Cannegieter at Leiden University Medical Centre.

DVT is the formation of a blood clot within an undamaged vein - often because lack of exercise prevents blood from being returned to the heart. Symptoms include pain, redness and swelling, and if part of the clot becomes dislodged it can lead to a life-threatening blockage in a blood vessel leading to the lungs. DVT kills around 3% to 5% of people with the condition.

Although the risk of DVT in airline passengers relative to the rest of the population has been studied a handful of times, the Dutch team is the first to work out the "absolute risk" of it occurring.

They surveyed 8,755 employees of large companies. Over five years 6,440 of them clocked up more than 300,000 flights. The rest did not fly at all. The team recorded all DVT cases in both flyers and non-flyers - 53 in all - and verified them with medical records. They calculate the risk of DVT among flyers is 3.2 for every 1,000 people a year compared with one every 1000 for non-flyers. The tallest flyers were at 3.6 times greater risk than non-flyers and the shortest were at 6.3 times greater risk, they report in the journal PLoS Medicine.

A spokesman for British Airways said DVT is not restricted to air travel. "Immobility as a causative factor in DVT has been recognised for many decades, as has the existence of certain groups who are at increased risk ... whether seated on a train, bus, theatre, car or at an office desk.

"We encourage passengers to remain active during flight and have even developed a series of exercises ... which can be undertaken without leaving the seats.

http://www.guardian.co.uk/science/2007/sep/25/travelnews.theairlineindustry