Blood clots are part of the body’s normal defense against bleeding. When a blood vessel is injured, blood becomes thicker and forms a clot to seal the damaged area.
Problems arise when a clot forms inside a blood vessel without a useful reason and blocks normal blood flow.
Clots in arteries can contribute to heart attacks and strokes. Clots can also develop in deep veins, most often in the legs, in a condition called deep vein thrombosis. If part of a clot breaks away and travels to the lungs, it can cause a pulmonary embolism, which can be life-threatening.
Many things can increase the chance of developing a dangerous clot, including older age, obesity, surgery, pregnancy, cancer and long periods of little movement. Genetics also matters. New research from Lund University in Sweden provides more evidence that a person’s inherited genes can strongly influence their risk.
The researchers studied about 30,000 participants from the Malmö Diet and Cancer Study, a large Swedish research project that has followed people’s health over many years. They examined genetic differences in 27 genes connected with blood clotting. The study identified several variants that were associated with a higher risk of clots in the veins.
Three genes stood out: ABO, F8 and VWF. These genes are involved in processes that influence blood groups and the body’s ability to form clots. Individual genetic variants were linked with roughly 10% to 30% increases in risk, according to the researchers.
The effect became much larger when people carried several risk variants at the same time. Those with five genetic risk factors had up to a 180% higher risk of developing a venous blood clot compared with people without those factors. This suggests that looking at combinations of genes may provide more useful information than examining a single gene.
Scientists already know about some inherited conditions that increase clot risk. One of the best known is Factor V Leiden, a genetic change that makes it harder for the body to switch off the clotting process. It is particularly common among people with European ancestry.
The newly studied variants could add to scientists’ understanding of inherited risk. Genes such as ABO and VWF have also been linked with clotting in previous research, and the new findings help show how several genetic influences can combine. This may partly explain why some apparently healthy people experience serious clots while others with similar lifestyles do not.
Genes, however, are only part of the picture. Blood moves more slowly through the legs when people remain still for long periods, such as during bed rest or lengthy travel. Surgery and serious illness can also increase clotting, while pregnancy naturally changes the body’s clotting system to reduce excessive bleeding during childbirth.
Body weight and age also influence risk. The chance of venous blood clots rises as people get older, and obesity is another established risk factor. Previous research has also found associations between greater height and clot risk, although a person’s overall risk depends on many factors working together.
People cannot change the genes they inherit, but some other risk factors can be reduced. Regular movement helps blood circulate through the legs, while maintaining a healthy weight and avoiding smoking can support cardiovascular health. People at particularly high risk may be given blood-thinning medicines before or after surgery or during other high-risk periods.
Anyone with possible symptoms of a clot should seek medical attention. A clot in the leg may cause swelling, pain, warmth or skin discoloration, usually on one side. Sudden shortness of breath, chest pain, coughing up blood or fainting can be signs of a pulmonary embolism and require urgent medical care.
The Lund University researchers believe genetic information could eventually help doctors estimate a person’s clot risk more precisely. For example, it might contribute to decisions about how long some patients should continue taking blood-thinning medicine after experiencing a clot. Such treatment must balance the danger of another clot against the risk of excessive bleeding.
The research, based on the Malmö Diet and Cancer Study, adds to growing evidence that venous blood clots result from a mixture of inherited and environmental factors. Better genetic risk estimates may eventually allow prevention and treatment to be tailored more closely to individual patients.
For now, awareness of both personal and lifestyle risks remains an important part of preventing dangerous blood clots.
If you care about heart health, please read studies about how vitamin D influences cholesterol levels, and what we know about egg intake and heart disease.
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