A report commissioned by the Department for Transport to determine the risk of deep vein thrombosis in relation to air travel, has found that as previously suspected, the longer the period of air travel, the greater the risk.
But possibly even more surprisingly it seems that multiple flights in a short period produce the same level of risk.
In the past DVT has been described as “economy-class syndrome”, and the most publicised cases have involved airline passengers.
It was found in the study that the people most at risk from developing DVT were those travelling for more than 12 hours, women using oral contraception and those taller than 1.9m (6ft 3in).
However the overall risk was found to be small and despite wide media coverage of such events only 1 per cent of DVT cases proves to be fatal.
The study which involved several research projects, found that all forms of transport involving a journey of four or more hours creates an increased risk of deep vein thrombosis ,which means travel by car or train also carries such a risk - in fact any form of transport where the passenger is in a position of enforced immobility.
The study found that people undertaking long journeys were three times as likely to develop blood clots in the veins of the legs, thighs or pelvis; these clots can be fatal if they travel to the lungs.
The project was funded by the Department for Transport, the Department of Health and the European Commission, and carried out by a consortium of medical research scientists under the umbrella of the World Health Organisation.