Updated on March 21, 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.
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. There are some variations by race, as well. For example, more African Americans and people of Asian descent are type B positive than are white people and people of Hispanic descent.
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
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, an observational study published in May 2018 in Critical Care looked at the medical records of 900 Japanese people admitted to emergency care medical centers for severe trauma between 2013 and 2016. Trauma-related death rates for those with type O blood were 28 percent, compared to 11 percent among those with other blood types.
While more research is needed to understand the link between blood type and post-trauma outcomes, the study authors suggest that type O blood contains lower levels of blood clotting agents, which may contribute to more bleeding.
Risk of heart disease and blood clotting conditions
Some researchers believe that people with types A, B, and AB blood have an increased risk of coronary heart disease, due to increased levels of inflammatory markers and certain proteins in the blood that lead to blood clotting. That translates into an increased risk of venous thromboembolisms. 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.) Estimates vary, but the most recent and rigorous studies put the risk of this type of blood clot at about double.
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 type A have a 24 percent higher risk of heart attack than people with AB or O blood types. For stroke, people with type AB blood have an 83 percent higher risk.
Risk of memory problems
A 2014 study published in Neurology of more than 1,000 people suggests that people with blood type AB have an 82 percent greater risk of cognitive impairment than people with other blood types.
On the other hand, type O may protect against memory problems, including Alzheimer’s disease. A 2015 study published in Brain Research Bulletin found that out of 189 people who had undergone brain MRIs, the brains of those with blood type O had the greatest amount of grey matter in their brains, providing possible protection against dementia.
Risk of stomach conditions
The link between blood type, stomach cancers, and peptic ulcers was first discovered in the 1950s.
Since then, additional research has provided further evidence of that link. In a 2010 study published in American Journal of Epidemiology, researchers looked at data from more than 1 million people. They found that people with blood type A had the highest risk for stomach cancers, while people with blood type O were at greater risk for developing peptic ulcers.
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.
But a more definitive answer has been uncovered by a major 2010 study from the Pancreatic Cancer Cohort Consortium (PanScan), which included 1,533 people with pancreatic cancer. The researchers found that those with blood type A with one specific gene mutation were at the highest risk. Another finding that most researchers agree on is that people with type O blood have the lowest incidence rate of 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 mother’s blood is separate from the baby’s blood. But during childbirth and in other cases, such as amniocentesis, the blood can mix. In this case, the mother’s immune system attacks the baby’s red blood cells.
“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 cells in the immune system.)
Symptoms of Rh incompatibility may be mild, causing jaundice 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. “The mothers had miscarriages pretty early on.”
Today, expecting mothers can get a special treatment called a RhoGAM shot to help avoid any Rh incompatibility. “It’s basically Rh factors injected into the mom so her body recognizes any Rh antibodies the baby has,” 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. 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.”
