Blood clots can form in both arteries and veins, but they happen for different reasons and carry different health risks.
While arterial clots are often linked to heart attacks and strokes, venous clots—especially those in the legs—can lead to serious conditions like pulmonary embolism, where a clot travels to the lungs and blocks blood flow. This type of clot is called venous thrombosis, and it’s more common—and more deadly—than many people realize.
In Sweden, more than 10,000 people experience venous thrombosis every year, and this number is growing. One reason is the aging population, since age is a major risk factor. But now, researchers from Lund University have found another reason: genetics.
In a new study published in Research and Practice in Thrombosis and Haemostasis, the team discovered three specific gene variants that can raise the risk of venous blood clots in the legs by as much as 180%.
This new finding builds on what we already know. In Sweden, nearly half of venous thrombosis cases have a genetic cause. For years, the most well-known inherited risk has been a mutation called Factor V Leiden, which makes people more prone to clots because their blood resists being broken down properly.
About 10% of Swedes carry this mutation, and it’s most common among people of Indo-European ancestry.
The Lund team’s new research identified three additional genetic variants—called ABO, F8, and VWF—that also affect how blood clots form. Each of these increases the risk by 10% to 30%, and people who have several of these variants face an even higher risk.
A person who carries five of these genetic markers has a 180% greater chance of developing a blood clot compared to someone without them.
Unlike Factor V Leiden, which is mostly limited to people of European descent, these newly identified gene variants are found in populations all over the world. This makes the discovery especially important for understanding and preventing clots on a global scale.
Venous clots usually happen when blood flow slows down too much—like when someone is on a long flight or stuck in bed after surgery. The blood pools in the legs, and without movement, the body’s natural clotting system may become overactive and form a blockage. If the clot breaks loose, it can travel to the lungs and become a medical emergency.
Several lifestyle factors can increase the risk. Being overweight or tall, for example, makes it harder for blood to flow back up from the legs to the heart. Sitting for long periods without moving also slows circulation.
The valves in the veins are supposed to keep blood flowing in the right direction, but if they’re damaged or under pressure for too long, clots can form more easily. According to lead researcher Professor Bengt Zöller, this is why taller people and those with a sedentary lifestyle are at greater risk.
Interestingly, some common health risk factors for arterial clots—like high blood pressure, high cholesterol, and smoking—don’t play a strong role in venous clots. Instead, venous clots are more influenced by body weight, inactivity, and inherited clotting traits.
Diet may also matter: ultra-processed foods are linked to a slightly higher risk, while healthy, plant-based diets may offer protection. Some research even shows that commercial fishermen have a lower risk, possibly because of their high intake of omega-3 fatty acids.
Pregnancy, surgery, and serious illness also increase the chances of a blood clot. During these times, blood becomes more likely to clot, and the veins may be damaged or compressed, which makes clot formation easier. In such situations, blood-thinning medications may be prescribed to prevent clotting—especially for people who already have genetic risks.
Now that researchers know more about these common gene variants, they hope to use this information to personalize treatment. For example, someone with multiple clotting-related genes may need longer or more aggressive treatment after experiencing a clot.
Zöller believes this is the future of medicine: using genetic risk scores to guide how long patients should stay on blood thinners and how closely they should be monitored. It’s part of a larger shift toward more tailored, precise care.
In summary, while lifestyle factors still matter, your genes play a big role in your risk of developing a venous blood clot. Thanks to new genetic research, doctors may soon be able to better predict—and prevent—these dangerous events before they happen.
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The research findings can be found in Research and Practice in Thrombosis and Haemostasis.
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