Blood clots can form in both arteries and veins. However, the causes vary, as do the consequences and the options for preventing blood clots. In Sweden, almost half of all cases of venous thrombosis are genetic. A team of researchers at Lund University in Sweden has now discovered three gene variants that increase the risk of blood clots in the legs by up to 180 percent. These discoveries build on existing knowledge about Factor V Leiden and suggest that genetics play a greater role than previously thought, particularly in clots in the legs that can lead to life-threatening pulmonary embolisms.
Arterial Versus Venous Blood Clots
There is a difference between arterial and venous blood clots. Blood clots in the arteries occur when plaque in calcified vessels breaks open and the body perceives this as an injury. This activates the blood platelets, which clump together and form a clot. In the worst case scenario, this can lead to a stroke or heart attack. A venous thrombus, on the other hand, usually forms in the leg if the blood stagnates for too long. This can activate the body’s coagulation system, causing the blood to clot and block the blood flow. If the clot breaks loose and enters the lungs with the blood, it can lead to a life-threatening pulmonary embolism.
“Venous thrombosis is actually one of the most common causes of death worldwide. It is a widespread disease that has so far been somewhat overshadowed by arterial blood clots,” says Bengt Zöller, specialist in general medicine at Skåne University Hospital and professor of general medicine at Lund University. In Sweden, more than 10,000 people suffer from venous thromboembolism every year, and this number seems to be increasing. Several factors contribute to this increase.
Factors that Increase the Risk of Thrombosis
One of the strongest risk factors is age, and as the number of older people in Sweden increases, so does the number of blood clots. Ten percent of 80-year-olds suffer a blood clot at some point. The risk also increases if you are overweight or tall. The muscles control the blood flow in the veins and the legs become fluid columns in which gravity has a strong effect. Too much sedentary and inactive activity is therefore harmful. Only the venous valves prevent backflow, and if these are damaged, the risk of blood clots can increase. Tall people are therefore more susceptible to blood clots, as their larger veins allow less blood to pass through and the blood has to travel a longer distance back to the heart.
As the heart pumps blood into the arteries, the blood pressure in the arteries is much higher than in the veins, which can contribute to arteriosclerosis. High blood pressure, high blood lipid levels and smoking are risk factors for arteriosclerosis. However, as the veins are a low-pressure system, arteriosclerosis does not occur in the vessels. Therefore, neither high blood pressure nor blood lipid levels are associated with venous blood clots, and smoking is only considered a weak to moderate risk factor. Obesity, on the other hand, is a very significant factor. Obesity has a negative effect on venous blood flow, especially in combination with the fact that overweight people are often less active. Some coagulation factors are also affected by obesity.
In terms of diet, there are fewer studies, but ultra-processed foods have been linked to a slightly increased risk of blood clots, while plant-based, healthy foods reduce the risk. In their studies, researchers have also found that professional fishermen have a lower risk, which may be due to a higher omega-3 content in their diet. There are also certain situations in which the risk of venous blood clots is particularly high. The risk of blood clots increases when blood flow is reduced, for example during long air travel or when lying in bed for several days. Operations or inflammations that damage the vascular wall can also lead to an increased tendency to clot. During pregnancy in particular, blood clotting factors increase and the level of some protective proteins can fall. In these risk situations, prophylaxis in the form of blood thinners can be particularly important if other risk factors are also present.
Other risk factors include genetic variants that influence different parts of the blood clotting ability. According to the researchers, there is a high prevalence of APC resistance (activated protein C) in Sweden due to an inherited mutation in the gene for coagulation factor V, the so-called factor V Leiden. Around 10 percent of Swedes carry this mutation, which is considered the most common coagulation mutation in Indo-Europeans.
Certain Gene Variants Greatly Increase the Risk
Bengt Zöller and his colleagues have now identified the strongest genetic risk factor since the discovery of factor V Leiden. They used data from the population-based Malmö Diet Cancer Study, in which 30,000 Malmö residents took part. By selecting 27 genes that had previously been associated with clotting disorders, they found three variants that together were as significant a risk factor for venous blood clots as factor V Leiden: ABO, F8 and VWF each increased the risk of venous blood clots by 10 to 30 percent. And the more of these variants a person has, the higher the risk. A person with five of these gene variants has a 180 percent higher risk of venous thrombosis. In contrast to Factor V Leiden, which only occurs in Indo-Europeans, these three different mutations are found in five to fifty percent of different population groups worldwide. As these genetic variants are found in all populations, the next step is to investigate how the number of risk genes affects the duration of anticoagulant treatment following a blood clot.
How to Prevent Blood Clots
- Exercise: Avoid sitting still for long periods. Stand up and move around on long flights.
- Support stockings: Can promote blood circulation if you have to stand or sit for long periods.
- Blood-thinning medication: Can be administered prophylactically in high-risk situations such as operations, cancer and other cases.
- Estrogen-containing birth control pills: Avoid estrogen-containing birth control pills or hormone replacement therapy if you have a strong predisposition to venous thromboembolism or if you have already had blood clots.
- Lifestyle changes: Quit smoking, eat healthier, lose weight and exercise.
- Get vaccinated: Infections can activate the clotting system.