International travel and health

Immobility, circulatory problems and deep vein thrombosis (DVT)

Contraction of muscles is an important factor in helping to keep blood flowing through the veins, particularly in the legs. Prolonged immobility, especially when seated, can lead to pooling of blood in the legs, which in turn may cause swelling, stiffness and discomfort.

It is known that immobility is one of the factors that may lead to the development of a blood clot in a deep vein – so-called “deep vein thrombosis” or DVT. Research has shown that DVT can occur as a result of prolonged immobility, for instance during long-distance travel, whether by car, bus, train or air. WHO set up a major research study, WHO Research Into Global Hazards of Travel (WRIGHT), in order to establish whether the risk of venous thromboembolism is increased by air travel, to determine the magnitude of the risk and the effect of other factors on the risk, and to study the effect of preventive measures. The findings of the epidemiological studies indicate that the risk of venous thromboembolism is increased 2- to 3-fold after long-haul flights (more than 4 h) and also with other forms of travel involving prolonged seated immobility. The risk increases with the duration of travel and with multiple flights within a short period. In absolute terms, an average of 1 passenger in 6000 will suffer from venous thromboembolism after a long-haul flight.

In most cases of DVT, the clots are small and do not cause any symptoms. The body is able to gradually break down the clots and there are no long-term effects. Larger clots may cause symptoms such as swelling of the leg, tenderness, soreness and pain. Occasionally a piece of a clot may break off and travel with the bloodstream, to become lodged in the lungs. This is known as pulmonary embolism and may cause chest pain, shortness of breath and, in severe cases, sudden death. This can occur many hours or even days after the formation of the clot in the leg.

The risk of developing DVT when travelling is increased in the presence of other risk factors, including:

  • previous DVT or pulmonary embolism
  • history of DVT or pulmonary embolism in a close family member
  • use of oestrogen therapy – oral contraceptives (“the pill”) or hormonereplacement therapy (HRT)
  • pregnancy
  • recent surgery or trauma, particularly to the abdomen, pelvic region or legs
  • cancer
  • obesity
  • some inherited blood-clotting abnormalities.

DVT occurs more commonly in older people. Some researchers have suggested that there may be a risk from smoking and from varicose veins.

It is advisable for people with one or more of these risk factors to seek specific medical advice from their doctor or a travel medicine clinic in good time before embarking on a flight of 4 or more hours.


The benefits of most recommended precautionary measures in travellers at particular risk for DVT are unproven and some might even result in harm. Further studies to identify effective preventive measures are ongoing. However, some general advice for such passengers is given here.

  • Moving around the cabin during long flights will help to reduce any period of prolonged immobility, although this may not always be possible. Moreover, any potential health benefits must be balanced against the risk of injury if the aircraft were to experience sudden turbulence. A regular trip to the bathroom, e.g. every 2–3 h, is a reasonable measure.
  • Many airlines provide helpful advice on exercises that can be carried out in the seat during flight. Exercise of the calf muscles can stimulate the circulation, alleviate discomfort, fatigue and stiffness, and may reduce the risk of developing DVT.
  • Hand luggage should not be placed where it restricts movement of the legs and feet, and clothing should be loose and comfortable.
  • In view of the clear risk of significant side effects and absence of clear evidence of benefit, passengers are advised not to use aspirin specifically for the prevention of travel-related DVT.
  • Those travellers at greatest risk of developing DVT may be prescribed specific treatments and should consult their doctor for further advice.