In a large study of nearly 2000 people with a first thrombosis in the Netherlands, Dr Suzanne Cannegieter and colleagues from the Leiden University Medical Centre looked at the risk factors for thrombosis. The results showed that 233 of the people with thrombosis had travelled for more than 4 h in the 8 weeks preceding the event.

Although the overall risk of developing thrombosis is still low, travelling in general was found to increase the risk of venous thrombosis 2-fold. The risk was highest in the first week after travelling, and the overall risk of flying was largely similar to the risks of travelling by car, bus, or train.

In particular groups of people the risk was increased. For example, the risk was up to 8-fold in people who also had a specific mutation in one of the genes involved in clotting (factor V Leiden); almost 10-fold in those who had a body mass index of more than 30 kg/m2; 4-fold in those who were more than 1.90 m tall; and more than 20-fold in those who used oral contraceptives.

For air travel these findings of risk in particular groups were more apparent than for other modes of travel, and in addition, people shorter than 1.60 m had an almost 5-fold risk of thrombosis after air travel. However, the numbers of people in each of these groups was small and hence the estimates of risk must be interpreted carefully.

The authors conclude that the risk of venous thrombosis is moderately increased for all these modes of travel, and that in particular groups of people the risk is highly increased. The study could not show the mechanism of the increased risk, although the association of thrombosis with all types of travel, not just air travel, suggests that immobility is a key factor.

MEDICA.de; Source: Public Library Of Science