Probably the only time you think about your blood type—if ever—is when there is a blood drive and you’re planning to donate, or if you (or someone close to you) are in the unfortunate situation of requiring a blood transfusion. You may know then whether you are type A, B, AB, or O, which is collectively referred to as the ABO blood group and is believed to have evolved from a distant ancestor millions of years ago.

Your blood type, inherited from your parents, refers to the specific antigens (molecules that can cause an immune response) found on the surface of your red blood cells. The ABO blood group results from one gene that has three variations: A, B, and O. Blood type A has A antigens, type B has B antigens, AB (the least common type in the U.S.) has both, and O (most common) has neither.

Before blood typing was discovered in the early 1900s, a blood transfusion could and often did have fatal consequences. That’s because the body’s immune system normally identifies and attacks foreign antigens, whether they are from bacteria that have entered the body, a transplanted organ, or anything else. In the case of blood type, if a person with type A receives type B blood, for example, specific immune proteins called antibodies will respond by attacking the B antigens, causing the red blood cells to clump, which can result in death. (Note that there are actually several other types of blood typing systems besides ABO that are addressed when blood is “typed and crossed-matched” prior to a blood transfusion.)

Blood type and disease risk

In the past century, and especially in recent decades, there’s been interest in how the ABO blood type may relate to disease risk. That is, are people with certain blood types more vulnerable to developing heart disease, cancer, or diabetes? Might your blood type even affect your memory or your response to diet? Here, in brief, is what we know.

Cardiovascular disease. In a 2012 study in Arteriosclerosis, Thrombosis and Vascular Biology, researchers looked at more than two decades' worth of data from 62,000 women in the Nurses’ Health Study and 27,000 men in the Health Professionals Follow-up Study. Blood type AB was associated with a 23 percent higher risk of cardiovascular disease, compared with type O, while type B was associated with an 11 percent higher risk, and type A, a 5 percent higher risk. Though it’s not clear what might account for this elevated risk, other research has linked blood type A with higher levels of LDL (“bad”) cholesterol, and type AB with an increase in inflammation, both of which can raise heart disease risk.

In a 2012 study in Arteriosclerosis, Thrombosis and Vascular Biology, researchers looked at more than two decades' worth of data from 62,000 women in the Nurses’ Health Study and 27,000 men in the Health Professionals Follow-up Study. Blood type AB was associated with a 23 percent higher risk of cardiovascular disease, compared with type O, while type B was associated with an 11 percent higher risk, and type A, a 5 percent higher risk. Though it’s not clear what might account for this elevated risk, other research has linked blood type A with higher levels of LDL (“bad”) cholesterol, and type AB with an increase in inflammation, both of which can raise heart disease risk. Cancer. In a 2015 study in BMC Medicine, investigators followed more than 50,000 people ages 40 to 70 for seven years and found that, after controlling for variables such as sex, education, and smoking, those with A, B, or AB blood type were at higher risk for developing stomach cancer (as well as of dying from heart disease), compared with people who were type O. There was no significant association between blood type and overall cancer mortality, however. A review paper in Future Science OA in 2016 noted that a genetic variation may increase the risk of pancreatic cancer among people with A or B antigens—in other words, A, B, or AB blood types. Meanwhile, as noted in the review, O blood type has been linked with a reduced risk of various cancers, including colorectal, stomach, and pancreatic. The American Cancer Society lists type A blood among the risk factors for stomach cancer (which also include H. pylori infection and tobacco use).

In a 2015 study in BMC Medicine, investigators followed more than 50,000 people ages 40 to 70 for seven years and found that, after controlling for variables such as sex, education, and smoking, those with A, B, or AB blood type were at higher risk for developing stomach cancer (as well as of dying from heart disease), compared with people who were type O. There was no significant association between blood type and overall cancer mortality, however. A review paper in Future Science OA in 2016 noted that a genetic variation may increase the risk of pancreatic cancer among people with A or B antigens—in other words, A, B, or AB blood types. Meanwhile, as noted in the review, O blood type has been linked with a reduced risk of various cancers, including colorectal, stomach, and pancreatic. The American Cancer Society lists type A blood among the risk factors for stomach cancer (which also include H. pylori infection and tobacco use). Diabetes. In a 2015 study in Diabetologia, researchers from France looked at health data from more than 82,000 women and found that type 2 diabetes was more likely to develop in those with type A and B blood, compared with type O.

In a 2015 study in Diabetologia, researchers from France looked at health data from more than 82,000 women and found that type 2 diabetes was more likely to develop in those with type A and B blood, compared with type O. Memory and stroke. In a 2014 study in Neurology of nearly 500 adults who had cognitive impairment, a greater proportion of them were type AB than any other blood type. In addition, AB blood type was associated with higher levels of a blood clotting protein compared with O type. Other research by the same investigators found that AB blood type was linked with a higher risk of stroke, which can result from a clot blocking blood flow to the brain.

In a 2014 study in Neurology of nearly 500 adults who had cognitive impairment, a greater proportion of them were type AB than any other blood type. In addition, AB blood type was associated with higher levels of a blood clotting protein compared with O type. Other research by the same investigators found that AB blood type was linked with a higher risk of stroke, which can result from a clot blocking blood flow to the brain. Malaria. It’s well known that people with type O blood have a degree of protection against the most dangerous form of malaria, which is caused by the mosquito-transmitted parasite Plasmodium falciparum (as opposed to less-dangerous species of Plasmodium). Among other effects, this parasite causes red blood cells to clump in our capillaries, resulting in severe tissue damage. To find out what accounts for this protection, Swedish researchers looked at a specific protein secreted by the malaria parasite and found that it tends to bind more tightly to red blood cells that are type A than type O. Their findings were reported in the journal Nature Medicine in 2015.

Blood type and diet

The idea that eating a diet aligned with your blood type can help you lose weight and reduce your risk for chronic diseases—and that eating a diet not aligned with your blood type can cause health problems—is the basis of the popular book Eat Right 4 Your Type, which was published in 1996. According to the author (and other advocates of blood type diets), people process food differently depending on their primary blood type, which is said to have evolved at different points in human history.

But such diets lack any scientific credibility. A systematic review of 16 well-controlled studies, published in the American Journal of Clinical Nutrition in 2013, concluded that though there is a possible link between certain blood types and increased vulnerability to particular diseases, as noted above, “there is currently no evidence that an adherence to blood type diets will provide health benefits, despite the substantial presence and perseverance of blood type diets within the health industry.”

Bottom line: The studies we reviewed suggest that blood type O is linked with lower health risks in general—though, with the exception of malaria, these are associations only, which do not prove cause and effect. Much more work is needed to determine how or even if blood type affects the risk for disease. Until we have more answers, rather than focusing on blood type, which can’t be changed, it’s more practical to work on lifestyle factors that can be modified, such as not smoking, exercising regularly, and eating a heart-healthy plant-based diet—steps known to help reduce the risk of many chronic diseases.