Researchers in Sweden have discovered three genetic variants that significantly increase the risk of blood clots in the legs, also known as venous thrombosis.
The study, conducted by scientists from Lund University, found that these genetic factors could raise a person’s risk by up to 180 percent. This new research adds to our understanding of why blood clots form and how to prevent them.
Blood clots can form in both arteries and veins, but they happen for different reasons. Arterial clots often result from plaque breaking off inside blood vessels, which the body treats as an injury.
This leads to clots that can cause strokes or heart attacks. Venous clots, on the other hand, usually happen in the legs when blood flow slows down. This can activate the clotting system and form a blockage. If the clot travels to the lungs, it can cause a dangerous condition called pulmonary embolism.
Venous thrombosis is a leading cause of death worldwide, but it often receives less attention than arterial clots. In Sweden, over 10,000 people are affected by venous thromboembolism every year.
The risk increases with age, obesity, and height. Tall people are more likely to develop clots because blood has to travel farther to reach the heart, and the blood flow in their leg veins is slower.
Unlike arteries, veins are low-pressure systems and do not usually suffer from conditions like high blood pressure or high cholesterol. However, obesity is a major risk factor for venous clots. It negatively affects blood flow, especially in people who are not physically active. Some clotting factors are also influenced by excess weight.
There is growing evidence that diet plays a role. Ultra-processed foods may slightly increase the risk, while plant-based, healthy diets may reduce it. Studies also found that commercial fishermen had a lower risk of clots, possibly because they eat more omega-3 fatty acids.
Blood clots are more likely during periods of low activity, such as long flights or bed rest after surgery. Pregnancy also increases the risk, as clotting factors rise and protective proteins may drop. In high-risk situations, doctors may prescribe blood-thinning medications to help prevent clots.
Genetics also play a major role. One well-known inherited mutation is Factor V Leiden, which affects about 10% of Swedes and is the most common clotting mutation among Indo-Europeans.
This mutation causes resistance to activated protein C (APC), which helps prevent clots. While APC resistance was useful in the past because it reduced bleeding, it has become a problem in today’s sedentary lifestyles.
In this new study, researchers examined 30,000 people in the Malmö Kost Cancer study and looked at 27 genes linked to clotting. They found that three gene variants—ABO, F8, and VWF—each increased clot risk by 10 to 30 percent. People with five of these risk genes had a 180 percent higher chance of developing a blood clot.
Unlike Factor V Leiden, which is mostly found in Europeans, these three variants are present in populations around the world. This means the findings could help people globally. The next step is to study whether the number of risk genes should influence how long people are treated with blood thinners after a clot.
To lower your risk of venous blood clots, you can:
– Stay active and avoid sitting for long periods
– Wear support stockings if you must sit or stand for long times
– Take blood thinners if advised after surgery or illness
– Avoid estrogen-based contraceptives if you have a history of clots
– Stop smoking, eat a healthy diet, lose weight, and exercise
– Get vaccinated, since infections can increase clotting risk
A blood clot is formed when blood thickens and blocks a vessel. This can happen in arteries (oxygen-rich blood) or veins (low-oxygen blood, often in the legs). Knowing your risk and staying active can help you stay safe.
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