Long-haul flights double the risk of blood clots, says WHO

30 June, 2007:

Your attention please: Passengers taking long-haul flights double the risk of developing blood clots that can lead to potentially fatal deep vein thrombosis (DVT).

The warning comes from the World Health Organization (WHO).

DVT occurs when a clot forms in leg veins during periods of relative immobility, such as long-haul travel. The clot can then migrate to the lungs in what is called a pulmonary embolism (PE), or the heart or brain, causing a heart attack or stroke.

The overall phenomenon is known as venous thromboembolism (VTE), the World Health Organization said in its project titled Research into Global Hazards of Travel.

Following five separate research studies as part of first phase of the project, the WHO said that “the risk of developing venous thromboembolism approximately doubles after travel lasting four hours or more.”

The absolute risk of developing VTE if seated and immobile for more than four hours remains “relatively low” at about one in 6,000, according to the WHO.

However, the chances are greater for people deemed at risk, for example, those who regularly take long-haul flights, those who are obese, either very tall or very short (above 1.9 meters and below 1.6 meters, or above 6 feet 3 inches and below 5 feet 3 inches), women who take oral contraception, or people with inherited blood disorders.

“It is a public health issue,” said Shanthi Mendis, WHO’s senior adviser on cardiovascular diseases, noting that about 2 billion people are estimated to fly every year.

The WHO stressed that the risks posed by immobility do not just apply to airline passengers but also those who undertake long journeys by car, bus or train.

According to the World Health Organization, travelers can take “commonsense” measures to reduce the risks of contracting VTE by regularly exercising their calf and ankle muscles during a journey, or simply getting up and moving around a little.

Passengers should also avoid taking sedatives or too much alcohol ahead of a voyage.

However, the WHO did not make any specific recommendations on prevention such as blood-thinning medications and elastic stockings which seek to prevent clotting, saying more research was needed into possible side-effects.

According to the WHO, there is a clear need for travelers to be given appropriate information regarding the risks. Further studies to identify preventive measures will be done under the second phase of the research project.