Exercise legs on long journeys, WHO advises

Passengers travelling for four hours or more face double the risk of developing potentially fatal blood clots, the World Health Organization said Friday in advising travellers on how to avoid it.

Deep vein 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, WHO assistant director-general for non-communicable disease and mental health.

"What causes the risk is immobility," she told a news conference in Geneva. "The risk is not only true for people flying."

Shanthi Mendis, a WHO expert on DVT, recommended that travellers:

• Get up for a short walk.
• Exercise their calf muscles with up-and-down movements of the feet and ankle joints every hour.
• Avoid taking sedatives or drinking large amounts of alcohol that increase the likelihood of staying immobile for too long.
• Avoid wearing tight clothing that restrictscirculation.

Obesity, genetic conditions, age, use of oral contraceptives, being shorter than five-foot-four or taller than six-foot-four all seem to increase the risk of DVT, also calledtraveller's thrombosis.

It's thought that the legs of short people dangle more, reducing mobility, while those of taller people end up cramped.

For the general population, the risk of developing blood clots from longer travels is one in 6,000, including small clots that don't cause symptoms, the UN agency said.

While the risk to any individual is tiny, becauseso many people fly, it becomes a public health issue, said Patrick Kesteven, a British doctor involved in WHO's 24-page report.