Updated on December 10, 2024.
Most people know their blood type—and you’ll definitely find out what it is if you ever need a blood transfusion or have an organ transplant. Your healthcare providers (HCPs) will take special care to use the blood type that matches, or is compatible with, yours.
A mismatch of blood types may cause an immune system reaction that could result in complications. These may include kidney damage or failure, blood clotting leading to organ damage or stroke, and, in more extreme cases, death. Fortunately, today’s testing techniques greatly reduce the chance of a mismatch.
Understanding blood basics
All blood has several essential pieces:
- Red blood cells carry oxygen and carbon dioxide to and from the lungs
- White blood cells are immune cells that help protect the body against invaders like viruses or bacteria
- Platelets clot together to prevent bleeding
- Plasma holds it all together
But there are differences between different blood types, as well. There are two antigens—A and B—on the surface of your red blood cells. Their presence or absence determines your blood type. An antigen is any kind of marker or sign that your immune system can learn to recognize. Viruses, tumors, bacteria, and regular cells all have antigens, and the immune system takes defensive action when it recognizes a harmful antigen.
Blood type is inherited, based on the blood types of both of your parents.
What’s your type?
There are four main blood types: A, B, AB, and O. Type A has the A antigen. Type B has the B antigen. Type AB has both. Type O has neither.
You may also be aware that your blood type is either positive or negative. But what does that mean?
There is a third antigen, a protein called the Rh factor, that may also be present on the red blood cells. If you have this protein, your blood type is positive. If not, your blood type is negative. Most people have a positive blood type.
Type O positive is the most common type in the United States. AB negative is the least common.
How blood type affects your health
Research suggests that certain blood types can raise your risk of potentially serious conditions, says Carla Bell, a genetic counselor at Wesley Medical Center in Wichita, Kansas. Obviously, it’s not possible to change your blood type, but being aware of your type can help you proactively take steps to reduce these risks.
Certain blood types may also be associated with a lower risk of certain diseases. In these cases, it’s good to know that your blood type may give you an extra health boost. Of course, regardless of your blood type, you’ll still need to make healthy lifestyle choices, like eating a nutritious diet and getting regular exercise.
Be aware of the risk of hemorrhage
Hemorrhaging, or losing a large quantity of blood, is common after severe trauma such as after a car accident or other injury. In many causes, hemorrhaging can be stopped and lost blood replaced by a transfusion. (A transfusion is a procedure during which additional blood is pumped into your body through a vein.) People with type O blood may be at a higher risk of uncontrolled bleeding, according to research.
For example, a 2021 study published in Acta Anaesthesiologica Scandinavica looked at more than 17,000 people who had cardiac surgery. People with type O blood lost the most blood, and people with type AB lost the least. Another 2021 study published in Vox Sanguinis found that in people who had total hip replacement surgery, those with type O blood lost the most amount of blood.
However, it’s still not clear how serious of a health risk this difference poses. A 2023 systematic review and meta-analysis published in Vox Sanguinis looked at 13 studies that examined blood group and trauma. Researchers found the rates of death after trauma were the same in patients with and without type O blood.
While more research is needed to understand the link between blood type and post-trauma outcomes, type O blood contains lower levels of blood clotting agents, which may contribute to more bleeding.
Risk of heart disease and blood clotting conditions
People with blood types in the A and B groups were found to have a 47 percent higher risk of developing a pulmonary embolism than people in the type O blood groups, according to 2020 research published by the American Heart Association (AHA). These are blood clots that travel to the lungs.
People in the type A and B groups were also 51 percent higher risk of developing deep vein thrombosis (DVT), compared to people with type O blood. These are blood clots that start in veins as opposed to arteries. (Arteries are blood vessels that carry oxygen-rich blood from the heart and lungs to the body, while veins are blood vessels that carry blood back from the body to the heart and lungs.)
Heart attacks and stroke are also clotting problems. If a clot blocks blood flow to the heart, that’s a heart attack. If it blocks blood flow to the brain, it’s a stroke.
People with blood types A and B have a combined 8 percent higher risk of heart attack than people with O blood types. For stroke, people with type A and B blood types have a combined 10 percent higher risk.
The silver lining for people with type A or B blood? A three percent lower risk of high blood pressure compared with people with type O blood.
Risk of memory problems
A 2021 review published in BioMed Research International looked at the data available on how different blood types raise disease risks. They noted that several studies have shown a connection between a higher risk of dementia and cognitive impairment and non-O blood type groups.
On the other hand, type O may protect against memory problems, including Alzheimer’s disease. Limited past research has found a possible correlation between having blood type O and having larger amounts of grey matter in the brain, providing possible protection against dementia. However, more studies are needed to confirm this link.
Risk of stomach conditions
The link between blood type, stomach cancers, and peptic ulcers was first discovered in the 1950s. A peptic ulcer is a sore that can occur inside your stomach on the lining, or in the upper part of your small intestine, usually caused by infection with a bacterium called Helicobacter pylori (H. pylori) or by using nonsteroidal anti-inflammatory drugs (NSAIDs) like ibuprofen for too long.
Since then, additional research has provided further evidence of that link. Type O blood has repeatedly been linked to a higher risk of peptic ulcers. And in a 2020 study published in the Scandinavian Journal of Surgery, researchers looked at data over 17 years from a cancer hospital and found that people with type A blood were at higher risk of gastric cancer, which confirmed past research. Meanwhile, people with AB blood type were at a lower risk. Types B and O were not more or less at risk.
Risk of pancreatic cancer
Pancreatic cancer is the third leading cause of cancer deaths in the U.S. This aggressive form of cancer also has one of the lowest survival rates. Since the 1940s, researchers have been aware of a link between blood type and pancreatic cancer. But over the years, study results as to which type poses the greater risk have been mixed.
In some cases, type A was believed to increase risk. Other studies of pancreatic cancer patients found a prevalence of blood type B. More recent studies have found that, in general, people with non-O blood type carry a greater risk.
In a 2021 review published in World Journal of Gastroenterology, researchers found that there is strong and growing evidence that people with blood type O have the lowest incidence of pancreatic cancer, and the best survival rates when they do develop it. Meanwhile, people with type A blood are at higher risk of developing pancreatic cancer.
Risks in pregnancy
Research has suggested that the A and B antigens play a role in disease risk. But what about the Rh factor? Rh factor comes into play during pregnancy, particularly if the mother has Rh-negative blood and the fetus’s blood is Rh-positive.
This is a condition known as Rh incompatibility. Usually, the pregnant person’s blood is separate from the fetus’s blood. But during childbirth and in other cases, such as amniocentesis, the blood can mix. (Amniocentesis is a procedure in which some of the fluid in the uterus is removed with a needle and syringe in order to test it.) When pregnant people with Rh-negative blood have a fetus with Rh-positive blood, their immune system attacks the red blood cells of their fetus.
“The body doesn’t usually react much during a first pregnancy,” notes Bell. “But in subsequent pregnancies, it can be a problem.” That’s because the first baby is born before antibodies have a chance to develop against the baby’s Rh-positive blood. Once formed, the antibodies stay in the body. (Antibodies are disease-fighting proteins made by the immune system.)
Symptoms of Rh incompatibility may be mild, causing jaundice (too much of a yellow pigment called bilirubin in the blood, which causes the eyes and skin to turn yellow) or low muscle tone. For more serious cases, complications to the baby can include:
- Lethargy
- Fluid buildup
- Brain damage
- Problems with movement, speech, and mental function
- Seizures
- Heart failure
- Death
“In the past, babies did not generally make it to term when there was Rh incompatibility,” says Bell, noting miscarriages happened early on.
Today, pregnant people can get a special treatment called a RhoGAM shot to help avoid any Rh incompatibility. “It’s basically injected Rh factors,” Bell explains.
Risk of malaria
Malaria is a disease caused by a parasite spread by mosquitos. It’s marked by symptoms including fever and anemia. In severe cases, it may lead to coma, and it kills about half a million people worldwide each year.
The disease is of particular concern to people who live in areas where malaria is common. These include parts of the world with warmer climates, especially sub-Saharan Africa. In fact, according to the World Health Organization, just four countries (Nigeria, the Democratic Republic of the Congo, Uganda, and Mozambique) make up more than half of all global malaria deaths. It’s also an issue for travelers and people who spend time in tropical locations.
Researchers believe that the parasite that causes malaria secretes proteins that stick to the surface of red blood cells. This makes the cells hard and causes them to attach to the walls of blood vessels. The proteins tend to stick more strongly to type A red blood cells, but more weakly to type O blood cells. “You don’t accumulate as much of the parasite in your body if you have type O blood,” says Bell. In other words, type O blood provides some protection against malaria (though it doesn’t provide actual immunity to the disease).
The bottom line
Your blood type may have some effects on your risk of having certain diseases. But for many conditions (like heart disease and cancer), your health habits, lifestyle, family history, and other factors matter much more.
“It’s important to remember that the effects of these are pretty small,” says Bell. “No one will be doomed to have a heart attack because of their blood type. For all people, the way to reduce their risk of disease is taking common-sense steps like no smoking. While it’s measurable, the net effect of blood type on disease risk is relatively small.”
