Passengers travelling for four hours or more face double the risk of developing potentially fatal blood clots, the UN health agency said on June 30 in advising travellers on how to avoid it.
The condition, known as venous thromboembolism (VTE), thrombosis or DVT is caused by sitting rigidly for too long. A blood clot forms in a deep vein, usually the calf or thigh, and may journey to the lungs, blocking blood flow.
"There is an increased risk of venous thromboembolism during travel where the passenger is seated and immobile over four hours, whether in a plane, train, bus or car," said Catherine Le Gales-Camus, World Health Organisation's assistant director-general for non-communicable disease and mental health.
"What causes the risk is immobility," she told a news conference in Geneva, according to a transcript issued at UN Headquarters in New York. "The risk is not only true for people flying."