Travellers who sit still on journeys lasting four hours or more have double the risk of developing potentially deadly blood clots, new research has found.
The World Health Organisation study says that train, bus or car passengers face a higher risk due to a ‘stagnation of blood in the veins caused by prolonged immobility.’
This can lead to deep vein thrombosis, or DVT, a condition in which a blood clot forms in the deep veins of the legs. The condition can be fatal if part of the clot breaks off and blocks a blood vessel in the lungs.
But the WHO points out that the risk is still relatively low – at about one in 6000 passengers.
One study within the project examining flights found that those taking multiple flights over a short period of time are also at higher risk.
This is because the blood clot risk does not go away completely after a flight is over, and remains elevated for about four weeks.
The report shows that a number of other factors increase the risk of blood clots during travel, including obesity, being very tall or very short (taller than 1.9 metres or shorter than 1.6 metres), use of oral contraceptives, and inherited blood disorders leading to increased clotting tendency.
Dr Catherine Le Galès-Camus, WHO Assistant Director-General for Noncommunicable Disease and Mental Health, said: ‘The study does confirm that there is an increased risk of venous thromboembolism (VTE) during travel where the passenger is seated and immobile for over four hours, whether in a plane, train, bus or car.
‘However, it is important to remember that the risk of developing VTE when travelling remains relatively low.’