Long haul flights treble risk of DVT

2007

The next time you're asked to jet off on a trans-continental business trip, you might want to reconsider. Because new research has revealed that long-haul flyers are three times more likely to develop deep vein thrombosis (DVT) than those whose feet stay on the ground.

Researchers from Leiden University Medical Center, Academic Medical Center Amsterdam and Nestle Medical Services monitored 8,755 employees of multinational companies for more than four years to find out how many developed the potentially fatal condition.

Over the period of the study almost 6,500 of them clocked up more than 300,000 flights with the remainder not taking any fights.

In the flyers group, 53 thromboses occurred, with 22 of these occurred within two months of them taking a long-haul flight.

The researchers calculated that DVT therefore occurs on average once in every 4,656 journeys and that people who take long haul flights have a 3.2 in 1000 chance of getting DVT compared with one every 1000 for non-flyers.

But these figures, the first to calculate the overall risk of DVT after air travel, are just averages. Throw in factors such as an individual's height or weight, age and gender and the numbers start to look even more alarming.

Those aged under 30, women using oral contraceptives and those who were particularly tall, short or overweight are far more likely to develop DVT.

Cramped into their seats with inadequate legroom, tall flyers are at 3.6 times greater risk than non-flyers. But the shortest passengers- whose feet cannot touch the floor and who therefore suffer from extra blood pressure behind the knees – are 6.3 times more likely to suffer from DVT.

Why the risk is higher among the under-30s remains unclear, however.

"The study clearly shows this could be prevented if seats were adjustable or there was more space," said Suzanne Cannegieter at Leiden University Medical Centre.

The risk also increases the longer someone flies, or the more times they fly in a short time, she said.

"The results of our study do not justify the use of prophylaxis (preventative treatment) such as anti-coagulant therapy for all long-haul air travellers, since this may do more harm than good," the report added.

"However, for some subgroups of people with a highly increased risk, the risk-benefit ratio may favour the use of prophylactic measures."

Older Comments

The discussion is not new, but it looks clear that from ~2000 people not flying of which apparently 2 developed DVT, no statistical conclusion can be drawn at all. The statistical uncertainty in the 'one in a thousand' risk is larger than the factor of 3.2 cited for the study. Splitting up the group into short and tall people decreases the statistical significance even further.

It is a pity that I did not find the original paper from which these results are taken.

Rob Hooft The Netherlands