Blood clots can form in both arteries and veins, but the reasons why they form are different. Arterial clots usually happen when plaque inside the arteries breaks, and the body treats it like an injury.
Platelets clump together and form a clot. If this happens in the heart or brain, it can cause a heart attack or stroke.
Venous clots, on the other hand, often form in the legs. They happen when blood flow slows down too much, like when someone sits or lies down for a long time.
This activates the body’s clotting system and forms a clot, which can block blood flow. If the clot travels to the lungs, it can cause a life-threatening condition called pulmonary embolism.
Venous thrombosis is one of the most common causes of death worldwide. In Sweden, over 10,000 people suffer from venous thromboembolism each year, and the number is growing. The risk increases with age, and about 10% of people over 80 will experience a clot.
Other risk factors include being overweight or tall, as tall people have longer veins and blood has to travel farther to return to the heart. If you sit still for too long, your leg muscles don’t help move the blood, making clots more likely.
Unlike arteries, veins are low-pressure vessels and don’t develop plaque. So high blood pressure, high cholesterol, and smoking aren’t major risk factors for venous clots. But obesity is a major risk factor, especially when it leads to inactivity. Obesity also affects the body’s clotting factors.
Studies show that people who eat more processed foods may have a slightly higher risk of clots, while a plant-based, healthy diet might reduce the risk. For example, commercial fishermen in Sweden have a lower risk, possibly because of the omega-3 fats in their diet.
Blood clots are more likely during long flights, bed rest, after surgery, or during pregnancy. In these situations, blood thinners may help prevent clots. Hormonal birth control or hormone therapy can also increase the risk if someone has a family history of clots.
Genetics also play a role. In Sweden, almost half of venous thrombosis cases are linked to inherited genes. One well-known mutation is Factor V Leiden, found in about 10% of Swedes. It makes people less likely to bleed but increases clot risk in modern sedentary lifestyles.
Now, researchers at Lund University have found three more gene variants—ABO, F8, and VWF—that also raise the risk of venous blood clots. These variants can be found in people all over the world.
The more of these variants someone has, the higher their risk. For example, a person with five of these risk genes has a 180% higher chance of developing a blood clot.
The next step for researchers is to see how these genes might affect the length of treatment with blood thinners after someone has a clot. Doctors may soon be able to tailor treatments based on a person’s genetic risk.
To reduce your risk of blood clots:
Move regularly, especially during long flights or if you sit for hours.
Use support stockings if you’re sitting or standing for a long time.
Take blood thinners if you’re in a high-risk situation like after surgery or during cancer treatment.
Avoid estrogen-based birth control or hormone therapy if you or your family has a history of clots.
Make healthy lifestyle changes: quit smoking, eat better, lose weight, and exercise.
Get vaccinated, as infections can trigger clotting.
A blood clot is a lump of solidified blood that can block blood flow. It can happen in arteries, where blood is rich in oxygen, or in veins, where blood is low in oxygen, usually in the legs.
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The study is published in Research and Practice in Thrombosis and Haemostasis.
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