Most of us think about health in terms of what we do — the foods we eat, how often we work out, how well we sleep, and how well we manage stress. Those things absolutely matter. But there’s another piece of the puzzle that many people forget: the part of our body we can’t change — our genes. One piece of genetic information you probably know, or have been asked for at some point, is your blood type. Most people think of this only when donating blood or in medical emergencies, but research over the past few decades has explored whether your blood type might be linked to risks for certain serious health problems, like heart attacks, blood clots, and strokes. In this discussion, we’ll explore what research says about blood type and health risk, including cardiovascular conditions, stroke, and other related issues, carefully noting what’s well established, what’s still uncertain, and what you can actually do about it.

When we talk about blood type in most health discussions, we’re referring to the ABO system, the most common system used in medicine. There are four main types: A, B, AB, and O. Each of these can also be Rh positive or Rh negative, depending on another protein on the blood cell surface called the Rhesus factor. That Rh factor doesn’t strongly influence heart disease risk on its own, so most research focuses on the ABO group. The way these blood types differ is based on tiny sugar molecules, called antigens, on the surface of red blood cells. Those antigens trigger immune responses and are why blood type matters for transfusions. But it turns out they may also affect processes inside the body, including clotting, inflammation, and protein levels that influence cardiovascular health.

Several large studies have looked at how blood type relates to the risk of heart attack and coronary artery disease. The broad pattern that emerges is that people with Type O blood tend to have a slightly lower risk of heart attack and heart disease, while people with Type A, B, or AB tend to have a higher risk when compared with Type O. One long-standing research review found that compared to people with Type O, Type A blood was associated with a modestly higher risk of coronary heart disease, and Types B and AB showed even larger relative increases. Another analysis suggested that people with non-O blood types may have a slightly higher risk, roughly around 8–10 percent more, of heart attack and heart failure than those with Type O. One leading idea is that people with non-O blood types have higher levels of certain proteins that influence clotting and inflammation, especially von Willebrand factor and factor VIII, both involved in the body’s clotting system. Higher levels of these proteins are linked with greater risk of clot formation and, ultimately, a higher likelihood of a heart attack if a clot forms in a coronary artery. Despite these associations, the actual differences in risk are relatively modest, and researchers emphasize that blood type by itself is not a dominant risk factor compared with things like smoking, high blood pressure, or high cholesterol.

One of the clearest areas where blood type seems to show a consistent pattern is in blood clotting risk. People with non-O blood types appear to have significantly higher rates of some types of dangerous clots, especially deep vein thrombosis, clots in deep veins usually in the legs, and pulmonary embolism, a clot that travels to the lungs. One large study found that people with blood types A, B, or AB were about fifty percent more likely to develop these kinds of clots compared with people who have Type O blood. This difference is likely tied again to differences in clotting proteins. People with Type O blood tend to have lower average levels of von Willebrand factor and clotting factor VIII, which may reduce the tendency of blood to form dangerous clots. On the other hand, lower von Willebrand factor levels in people with Type O can also mean a slightly higher bleeding tendency in some medical situations, such as during certain surgeries, but that’s a separate issue and not the primary focus when discussing heart attack or clot risk.

Risk for stroke, particularly ischemic stroke, which is caused by a blockage of blood flow to the brain, has also been studied in relation to blood type. Multiple lines of evidence suggest that people with Type O blood tend to have a lower risk of some types of stroke, while people with Type A, B, or AB blood seem to have higher risk for ischemic stroke compared with Type O. One genetic analysis showed that people with Type O were underrepresented in groups that suffered early-onset ischemic stroke compared with people with other blood types. Other research shows that individuals with non-O blood types may also have differences in the way cholesterol is handled in the body, which itself affects blood vessel health and stroke risk. Even with these findings, many other factors influence stroke risk much more strongly, including high blood pressure, diabetes, smoking, and age. Blood type is only one piece of a much bigger picture.

There’s also been research suggesting possible links between blood type and the risk of certain cancers, especially pancreatic cancer. Some earlier studies hinted that non-O blood types might have slightly higher colorectal cancer risk, but the evidence is mixed and not conclusive. In colorectal cancer specifically, large datasets have not consistently shown a significant difference in cancer rates when comparing blood types. So while this remains an area of interest, the evidence doesn’t support strong conclusions yet.

If you take away one thing from all this research, it’s that blood type may influence your risk, but it’s just one of many risk factors. Blood type might give a small risk signal: people with Type O blood seem to have a slightly lower tendency toward blood clots, heart attacks, and some strokes, while people with non-O blood types may have a modestly elevated risk of the same conditions. But lifestyle and established medical risk factors matter more. Smoking, lack of exercise, obesity, high blood pressure, high cholesterol, and poor diet all have stronger, well-proven effects on heart and stroke risk than blood type itself. Blood type shouldn’t make anyone complacent or overly worried. It’s not a guarantee of good or bad health. Blood type is also not something you can change, and while it may offer another small piece of information in understanding risk, it’s not modifiable. What is modifiable are things like diet, exercise, and blood pressure, which are far more powerful determinants of long-term health.

Regardless of your blood type, the same basic strategies are recommended for reducing risk. Eat a balanced, nutrient-rich diet with plenty of vegetables, fruits, whole grains, lean proteins, and healthy fats. Stay active with regular aerobic exercise and strength training. Maintain a healthy weight, as being overweight increases risk for many diseases. Manage stress, because long-term stress can affect heart health. Avoid smoking, as smoking dramatically increases cardiovascular risk. Limit alcohol and control blood pressure and cholesterol through lifestyle and, when needed, medication. Finally, see your doctor for regular checkups, especially if you have a family history of heart disease or stroke. These steps benefit everyone, regardless of ABO blood group.

Your blood type is part of your genetic identity, and research shows it’s connected in subtle ways with your risk for blood clotting, heart attacks, and strokes. People with Type O blood seem to have the lowest risk for these events compared with other types, likely because of differences in clotting factors in the blood. But it’s just one piece of the health puzzle, and not the biggest one. The most powerful things you can do for your heart and vascular health are choices you can control: how you eat, how you move, and how you manage stress and other medical conditions. If you think you might be at risk for heart disease, stroke, or blood clotting problems, talk with a healthcare provider. They can help you understand your personal risk and make a plan that fits your health needs and lifestyle.