Are you worried about deep vein thrombosis? Stay healthy in the air with our safe-flight guide

What is DVT?
Deep vein thrombosis or DVT is a condition of the circulatory system, where blood clots develop in the deep veins of the legs. It's fairly rare, occurring in one or two per thousand - mainly older - people.

What is the link between DVT and flying?
A French study has shown that journeys more than five hours long by car, plane or train increase the risk of DVT fourfold. There is particular risk with air travel because the combination of inactivity and dehydration leads to stickier blood.

What are the symptoms?
Quite often there are no symptoms at all. If there are, you'll suffer from swelling and pain that becomes more severe over time. Skin may feel warm or itchy and tender. Flexing the foot upwards is painful, though not always. Some people feel dizzy or feverish. Skin may become discoloured and surface veins more visible.

Why is it nicknamed Economy Class Syndrome?
Originally, the cause of DVT was linked to the squashed conditions in the cheaper seats in airplanes. It was also linked with long-haul flights. However, research has shown that it happens in all classes of seating, and also that the risk of DVT is just as likely at three hours or nine.

Who is most at risk?
For most healthy people, the risk is minimal. The risk increases for the over-40s. However, women on the pill or undergoing hormone replacement therapy are at medium risk because their medication increases the chance of clotting. Pregnancy and obesity increase the risk, too. Most at risk are those with a previous history of blood clots or pulmonary embolism. Those with varicose veins or blood clots, or a family history of blood clots, have an increased risk. If you've recently undergone major surgery - orthopaedic surgery or treatment for cancer - you should avoid flying for at least 90 days after treatment.

How can I protect myself?
Aviation Health Institute, the charity promoting healthy air travel, recommends that travellers follow these simple measures to reduce the risk of DVT.

• Keep your thighs clear of the edge of the seat and keep your feet elevated - try resting them on your hand luggage
• While flying, do the exercises recommended by the airlines. Five minutes of toe and heel presses and ankle rotations every hour gets stagnating blood on the move. Keep walking around the cabin
• Drink plenty of water to prevent dehydration and avoid drinking too much alcohol
• Wear flight socks. A recent study in the medical journal, The Lancet, showed that as many as one in ten passengers could suffer from DVT, unless they wear the special compression stockings. This is particularly important for passengers suffering from varicose veins.
• Take a low-dose aspirin (100-150mg) the day before and during a long-haul flight, and for three days after.
• Walk briskly for at least half an hour before take-off.