Most people think about their blood type only when they donate blood, need a transfusion, or fill out a medical form.
But scientists have found that the ABO blood groups – A, B, AB, and O – may also be linked to small differences in the risk of several diseases.
Blood type is determined by molecules called antigens on the surface of red blood cells.
These inherited features help the immune system recognize the body’s own cells, but they can also affect blood clotting and the way some germs interact with the body.
One of the clearest connections involves blood clots. Research published in journals including Seminars in Thrombosis and Hemostasis has found that people with non-O blood types – A, B, or AB – have a higher risk of venous blood clots than people with type O.
This may partly be explained by differences in proteins that help blood clot. People with type O generally have lower levels of von Willebrand factor and factor VIII, two proteins involved in clot formation, which may reduce their tendency to develop dangerous clots.
Blood type has also been studied in relation to heart disease. Some large studies have found a modestly lower risk of coronary heart disease among people with type O compared with people who have A, B, or AB blood, although blood type is only one of many factors involved.
The important point is that having a particular blood type does not mean a person will or will not develop heart disease. Smoking, blood pressure, cholesterol, diabetes, exercise, diet, age, and family history usually matter far more when doctors assess someone’s cardiovascular risk.
Researchers have also investigated links between blood type and cancer. A meta-analysis published in the International Journal of Molecular Sciences found that people with type A blood had a slightly higher risk of stomach cancer, while people with type O had a slightly lower risk.
One possible explanation involves Helicobacter pylori, or H. pylori, a bacterium that can live in the stomach. Long-term infection can cause ulcers and inflammation and is an important risk factor for stomach cancer, and some research suggests that susceptibility to this infection may differ slightly by blood group.
Other cancers have also been examined, but the picture is complicated. A large review covering millions of people found statistical links between ABO blood groups and several cancers, yet these associations were generally modest and do not mean that blood type directly causes cancer.
Blood type may also influence the body’s response to certain infections. For example, type O has long been associated with some protection against severe malaria, although it does not prevent a person from becoming infected.
During the COVID-19 pandemic, researchers also examined whether ABO blood type affected the chance of infection or severe illness. Early studies reported possible differences, but later evidence showed that any effect was too small and inconsistent to use blood type as a meaningful guide to personal COVID-19 risk.
Scientists are even studying whether blood group is related to the bacteria living in the digestive system. Because ABO-related molecules are found in several tissues and body fluids, they may influence which microbes are able to thrive, but this area of research is still developing.
None of this supports the popular idea that people should choose foods according to their blood type. So-called blood type diets claim that people with A, B, AB, or O blood require different foods, but research has not provided convincing evidence that matching a diet to ABO type improves health.
Instead, the strongest health advice remains familiar: do not smoke, stay physically active, eat a balanced diet, maintain a healthy weight, get enough sleep, and manage blood pressure, cholesterol, and blood sugar. These factors have much greater effects on long-term health than whether someone has A, B, AB, or O blood.
Blood type is therefore best viewed as one small piece of a much larger biological puzzle. It can help researchers understand why disease risks differ between people, but it should not be treated as a prediction of an individual’s future health.
Knowing your blood type is important for transfusions and certain medical situations. When it comes to staying healthy, however, focusing on the risk factors you can change is likely to make a much bigger difference.
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