Risk of DVT on planes so small... not worth taking pills

The debate over the health risks associated with long-haul flights is in the news again with research from Holland.

The Dutch researchers were particularly interested in assessing the absolute risks of developing deep-vein thrombosis (DVT) from air travel.

To arrive at some form of satisfactory risk measurement the Dutch team conducted a survey of 8,755 employees of international companies, with an average age of 40, to collect data about their patterns of travel and the incidence of DVT.

This study is the first attempt to assess the absolute risks of air travel, and it involved the tracking of the study participants for more than four years.

In that time they recorded 53 thromboses, 22 of which occurred within eight weeks of a long-haul flight.

The researchers calculated that there was an incidence rate of 3.2 thromboses per 1,000 people per year in those who make long-haul flights, compared to 1 per 1,000 per year in those who do not.

They say the risk of one event per 4,656 long-haul flights is so small that it is not worth taking anticoagulant drugs, such as aspirin, to protect against it.

The team led by Frits Rosendaal, of Leiden University Medical Centre, say the results do not justify the use of potentially dangerous prophylaxis such as anticoagulant therapy for all long-haul air travellers, since this may do more harm than good.

However they say such measures may benefit people with high risk.

The team found the risk of thromboses increased with exposure to more flights within a short period of time, and with longer flights.

They say it was particularly high in people under 30, in women who used oral contraceptives, and in those who were particularly short, tall or overweight.

Thromboses occurred most often within the first two weeks after travel.

Flying has been linked with blood clots for more than five decades, but this is the first study which has actually calculated the true risk.

Many airlines now offer in-flight exercise plans to reduce the risk.

The study is published in the Public Library of Science journal PLoS Medicine.