Whether you’re jetting off for some winter sun, a half-term family break or a summer escape, if you’ve got any long-haul flights booked this year, it’s important you understand how to prevent deep vein thrombosis (DVT) while you’re in the air.

By following some simple do’s and don’ts, you can reduce your risk of developing a blood clot forming in your leg, causing pain and potentially ruining your holiday.

To mark DVT Awareness Month in March, doctors explain everything you need to know about preventing the condition…

What is DVT?

“Deep vein thrombosis is the formation of a blood clot, generally in the lower limbs, but it can occasionally occur in upper limbs,” says personal physician and private home visiting GP Dr Suhail Hussain (drsuhailhussain.com).

The condition is believed to affect around one in every 1,000 people in the UK, and usually only occurs in one leg.

“Possible symptoms of DVT can include a painful or tender leg for no obvious reason – this can be above knee, below knee or both,” says Professor Mark Whiteley, leading venous surgeon and founder of The Whiteley Clinic (thewhiteleyclinic.co.uk).

Swelling can occur from the ankle upwards or even the whole leg, he says. “Other symptoms include a heavy ache in the leg, especially on standing or walking; warm skin in the area of swelling; and sometimes the skin can be a bit redder, but this is less common.”

Generally, DVT is not a major problem as long as it is diagnosed and treated immediately, but complications can occur.

“It can develop into PE (pulmonary embolism), a blood clot on the lung which can be life-threatening, so [we] should not ignore signs and symptoms of DVT,” Hussain says.

DVT is generally diagnosed via an ultrasound scan. The main treatment is anticoagulant medicine such as warfarin or rivaroxaban.

“If there are recurrent DVTs in the same leg, the deep veins can become scarred and stop working properly,” Whiteley says.

“This causes ‘post-thrombotic syndrome’ (PTS), which can cause chronic pain and swelling of the leg, with discolouration and often leg ulcers.”

Why does DVT occur on long-haul flights?

One of the risk factors for DVT is long periods of inactivity, which is why it’s more likely to occur on lengthy flights.

“According to the latest research from NICE, the risk of developing DVT is increased two- or threefold after long-haul flights, meaning those more than four hours,” Whiteley explains.

“This is a higher risk than other modes of transport where there is prolonged seating and immobility.”

Other medical factors can play a part, he warns: “Such as having a family history of DVT, large varicose veins or cancer, people who are pregnant or have recently undergone major surgery.”

Stretch your legs

The most important thing you can do to prevent DVT is not stay in your seat for the whole flight.

“Go for a walk up and down the cabin aisle at least once per hour, particularly if it is a flight over four hours,” says Whiteley.

Hussain recommends walking around even more frequently: “Get up around every 20 to 30 mins if possible – sit in the aisle to aid getting out of your seat.”

While seated, keep your legs moving, he adds: “Try calf exercises – most airlines have a booklet in the seat pocket. A simple one is to regularly flex and extend your ankles.”

Stay hydrated

Hydration is also key for preventing DVT, Whiteley says. “Dehydration affects the constituents of the blood, making blood thicker and more ‘sticky’ – blood flows at a slower rate in veins than in arteries.

“Therefore, being dehydrated can increase the chances of developing a blood clot in the veins.”

While it may be tempting to indulge in a cold beer or glass of wine with dinner, you’d do better sticking primarily to H2O.

“Drink plenty of fluids including water, diluted squash, herbal teas and fruit juice while flying, especially if you have other risk factors for blood clots,” Whiteley advises.

“Tea and coffee contain caffeine, which actually causes you to lose water. Hence these, and alcohol, can make dehydration worse, and should be consumed at a minimum on flights.”

Hussain also recommends avoiding sleeping pills or alcoholic drinks that will cause you to drift off. “If you’re sleeping you can’t get up,” he adds.

 Wear compression socks

“Wear compression stockings providing 15 to 30mmHg pressure at the ankle,” while traveling, says Hussain, which means ‘millimetres of mercury’, or the compression level.

Make sure you wear the correct size – and you don’t need to wear regular socks at the same time.

“Compression socks speed up the flow of blood in the veins and therefore reduce the risk of the blood clotting,” Whiteley suggests.

“Research has confirmed that ‘travel socks’ reduce the risk of developing DVT.”

Avoid flying if you’re high risk

“Once you’ve had one blood clot, the risk of a subsequent one increases,” Hussain warns, which is why he advises avoiding flights if you’ve had DVT recently.

“I saw a young guy who had a DVT and I advised him to not fly for at least four weeks afterwards. Blood thinning medication (heparin) can be given if the patient absolutely must fly.”