The deadly condition that strikes on holiday – and 7 ways to prevent it
CROWDED airports, lengthy check-in queues, narrow seats and long-haul travel delays all bring extended periods of sitting and standing still.
This is only worsened when travelling in economy class, where conditions tend to be pretty cramped.
Well with this comes a risk of developing deep vein thrombosis (DVT) - a blood clot in a vein that can be fatal.
While usually found in the leg, it can move to the lungs and cause a life-threatening pulmonary embolism, which can kill very quickly.
It is sometimes dubbed "economy class syndrome" as some research has shown it to be more common in those towards the back of the plane - though it can happen anywhere.
It's due to the sitting posture, tight seating arrangements and prolonged immobility which can compress the blood vessels and lead to blood pooling, scientists say.
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One study in 2021 found air travel longer than eight hours increased someone's risk of developing DVT.
Another, published in the New England Journal of Medicine, showed DVT was significantly more prevalent in passengers on long-haul flights (more than six hours) than in the general population.
A third, in Brazil, blamed it on immobilisation, decreases in air pressure and low humidity.
Body mass index (BMI), age, surgical history, oral contraceptives, hormone replacement therapy (HRT) and cancer also made people more predisposed.
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The Centers for Disease Control and Prevention says: "More than 300 million people travel on long-distance flights (generally more than four hours) each year.
"Blood clots, also called deep vein thrombosis (DVT), can be a serious risk for some long-distance travellers.
"They can form in the deep veins of your legs during travel because you are sitting still in a confined space for long periods of time.
"The longer you are immobile, the greater your risk."
Around one in 1,000 people in the UK will develop DVT every year, according to the NHS.
It can happen to anyone, but those over 40 are most at risk.
Other risk factors include a family history of blood clots, being inactive for long periods, blood vessel damage, heart and lung disease, and being overweight or obese.
Taking the combined contraceptive pill and HRT can also increase your chances as both cause the blood to clot more easily.
Thankfully, there are some things you can do - both before, during and after travel - to reduce your risk.
Before travelling
1. Avoid smoking
Smoking causes blood vessels to narrow and become blocked, according to the NHS.
So refraining from lighting up before a flight should reduce your risk of DVT.
Dr Rob Hicks said: "Not smoking is an essential step to improving circulation.
"It hinders your blood from circulating as it should by damaging and narrowing your arteries.
"After just 20 minutes without smoking, your pulse rate is beginning to return to normal.
"And blood circulation improves after two to 12 weeks without a cigarette."
2. Cut down on fast food
Studies show eating a healthy diet which is low in ultra-processed foods is linked to a lower body weight and therefore a reduced BMI.
As a high BMI is a major risk factor for DVT, some weight loss should be beneficial.
This is because obesity leads to stasis or stagnation of blood in the veins, giving you a higher chance of thrombosis and clot formation.
When travelling
3. Stay hydrated
Many people choose not to drink too much during a long journey to avoid frequent bathroom visits, but it's vital to take on enough fluids.
If you are dehydrated, your blood will thicken, your circulation will worsen and you will be more prone to clotting.
Be sure to drink plenty of water, and try to avoid excessive caffeine or alcohol as they can contribute to dehydration.
4. Wear compression socks
If you are at increased risk of DVT, compression stockings or socks are sometimes recommended, the NHS says.
It is important to get the right size, as incorrectly fitted garments can actually increase your risk further.
Fit for Travel, which is run by the health service, advises speaking to your GP for guidance.
5. Keep active
Sitting or standing for long periods is a major risk factor in the development of blood clots.
These prolonged periods of immobility can lead to slow blood flow in the veins, and ultimately develop into a clot within a deep vein.
Something as simple as getting up, walking down the aisle and around the cabin to stretch your legs can improve blood flow, according to Fit for Travel.
While in your seat, ankle circles, leg lifts, shoulder rolls, neck stretches and wrist movements are also good ways to keep moving, reduce muscle tension and boost circulation.
6. Ask for an upgrade
DVT may sometimes be known as 'economy class syndrome' - but this can be misleading.
Dr Sarah Brewer previously told The Sun: "The problem isn't just confined to economy class, or to long haul flights.
"People flying in business and first class - even on flying beds - have also been affected, and some deaths have been linked with short haul flights.
"Any long distance journey lasting four hours or more doubles your risk of a venous thrombosis, however you travel - whether by plane, car, coach or train."
That being said, having more room gives you more opportunity to move about.
So if possible, pick an aisle seat so you have more freedom to roam.
Even better, ask for an upgrade where you'll get a wider seat and more legroom.
When home
7. Get moving
When you're back from your trip and perhaps returning to work, try to maintain some level of physical activity.
If your job involves sitting at a desk for example, why not try setting a timer to remind yourself to get out of your chair at regular intervals?
Research shows DVT can strike up to eight weeks after your get home.
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The advice was compiled in part by the .
For any concerns about your health, please contact your GP or the NHS 111 line prior to travelling.