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A new analysis of research shows that your blood type may play a role in your risk of having an ischemic stroke. However, the additional risk is very small and is not on par with other risk factors such as high blood pressure or diabetes thatraise your risk of stroke a lot more.

The finding comes from a recent meta-analysis of 48 studies that looked atgeneticsand ischemic stroke. Combined, the studies included data and genetic information from more than 16,700 people who had a stroke and nearly 600,000 people who had not had a stroke who served as controls.

For their analysis, the researchers compared the prevalence of genetic variants for the different blood types in people who had a stroke before age 60 (early-onset stroke), a stroke later than age 60 (late-onset stroke), and people who had not had a stroke.

How Can You Find Out Your Blood Type?

After analyzing the gene data from all the studies and looking for associations between genetic variants and stroke, the researchers found a link between stroke—especially stroke before age 60—and the genes that determine blood type.

How Does Blood Typing Work?The ABO Blood TypesThere are four basic blood types in the ABO system. They’re based on the presence or absence of type A and Bantigens:Type A bloodhas A antigens (about 40% of people have this type)Type B bloodhas B antigens (about 10% of people have this type)Type ABhas both antigens (about 5% of people have this type)Type Oblood has neither antigen (about 45% of people have this type)Rh FactorEach blood type can be also either RH positive or negative, which means that a protein calledRhesus factor (Rh)is either present or absent. Having an RH-negative blood type is much rarer than having an Rh-positive type.

How Does Blood Typing Work?

The ABO Blood TypesThere are four basic blood types in the ABO system. They’re based on the presence or absence of type A and Bantigens:Type A bloodhas A antigens (about 40% of people have this type)Type B bloodhas B antigens (about 10% of people have this type)Type ABhas both antigens (about 5% of people have this type)Type Oblood has neither antigen (about 45% of people have this type)Rh FactorEach blood type can be also either RH positive or negative, which means that a protein calledRhesus factor (Rh)is either present or absent. Having an RH-negative blood type is much rarer than having an Rh-positive type.

The ABO Blood Types

There are four basic blood types in the ABO system. They’re based on the presence or absence of type A and Bantigens:

Rh Factor

Each blood type can be also either RH positive or negative, which means that a protein calledRhesus factor (Rh)is either present or absent. Having an RH-negative blood type is much rarer than having an Rh-positive type.

How Could Blood Type Affect Stroke Risk

According toBraxton Mitchell, PhD, MPH, a co-author of the study and professor of medicine and of epidemiology and public health at the University of Maryland School of Medicine, the factors that separate blood types A and B (higher stroke risk) from O (lower stroke risk) appear to increaseblood clotting.

In the meta-analysis, the researchers also looked at whether blood type affected the incidence ofblood clots that form in veins(venous thromboembolismor VTE).

“We thought that if blood group A is really predisposing to clotting, maybe blood group A would be related to some of these other conditions like VTE,” said Mitchell. “The answer is yes.”

What Causes a Stroke?

Why Analyze Blood Type and Stroke Research?

A meta-analysis lets researchers combine the results of multiple scientific studies and statistically analyze all of the information. Whenmany studieshave asked the same question, a meta-analysis can provide clearer results than each of the individual studies could.

With the latest blood type and stroke research, the ability to analyze health information and gene sequencing from a lot of people through meta-analysis made finding the association possible.

“Blood group has been associated with stroke before, so that in itself wasn’t novel,” Mitchell said. “But what was novel is that the association of blood group with early onset stroke was much stronger than it is for later onset stroke.”

However, Mitchell pointed out that a limitation of the meta-analysis was that the populations in the original study lacked diversity—the original studies had been conducted in North America, Europe, and Asia.

Daniel Lackland, DrPH, a professor of neurology and epidemiology at the Medical University of South Carolina, told Verywell that the research “is a very large meta-analysis and it’s from populations all over the world” but agreed that “there’s a little bit of issue that these are fairly select studies.”

Why Do I Need to Know My Blood Type?Knowing your blood type is important should you ever need a blood transfusion. Your blood type determines what blood you could get, as well as who could receive blood that you’ve donated:Type O blood (no A or B antigens)can be given to anyoneType AB blood (both A and B antigens) can receive any type of bloodA transfusion of blood that is not compatible—for example, someone with type A getting type B blood—can cause a reaction.

Why Do I Need to Know My Blood Type?

Knowing your blood type is important should you ever need a blood transfusion. Your blood type determines what blood you could get, as well as who could receive blood that you’ve donated:Type O blood (no A or B antigens)can be given to anyoneType AB blood (both A and B antigens) can receive any type of bloodA transfusion of blood that is not compatible—for example, someone with type A getting type B blood—can cause a reaction.

Knowing your blood type is important should you ever need a blood transfusion. Your blood type determines what blood you could get, as well as who could receive blood that you’ve donated:

A transfusion of blood that is not compatible—for example, someone with type A getting type B blood—can cause a reaction.

Should I Worry About My Blood Type and Stroke Risk?

If blood type does affect stroke risk, that information is mostly a curiosity at the moment. People cannot change their blood type—outside of some very unusual circumstances like having a bone marrow transplant.

“Should people with blood group A be worried? I would say no, you should not be worried,” said Mitchell. “The risk from having blood group A is smaller than that for other modifiable risk factors for stroke.”

According to Mitchell, “we should really be tackling things like hypertension and smoking,” when it comes to stroke risk. “Those are the things that we should go after because they’re modifiable and have bigger effects.”

Lackland agreed, adding that while the link between blood type and stroke risk should be researched more, for now, no one with blood type A should be alarmed.

What This Means For YouYour blood type might have a very small effect on your risk for a stroke, but it’s not as important as other risk factors.You can’t change your blood type but you can make changes in your life that can help lower your stroke risk, like quitting smoking and managing your blood pressure.

What This Means For You

Your blood type might have a very small effect on your risk for a stroke, but it’s not as important as other risk factors.You can’t change your blood type but you can make changes in your life that can help lower your stroke risk, like quitting smoking and managing your blood pressure.

Your blood type might have a very small effect on your risk for a stroke, but it’s not as important as other risk factors.

You can’t change your blood type but you can make changes in your life that can help lower your stroke risk, like quitting smoking and managing your blood pressure.

2 SourcesVerywell Health uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read oureditorial processto learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.Jaworek T, Xu H, Gaynor BJ, et al.Contribution of common genetic variants to risk of early onset ischemic stroke.Neurology. Published online August 31, 2022. doi:10.1212/wnl.0000000000201006American Red Cross.Facts about blood and blood types.

2 Sources

Verywell Health uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read oureditorial processto learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.Jaworek T, Xu H, Gaynor BJ, et al.Contribution of common genetic variants to risk of early onset ischemic stroke.Neurology. Published online August 31, 2022. doi:10.1212/wnl.0000000000201006American Red Cross.Facts about blood and blood types.

Verywell Health uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read oureditorial processto learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.

Jaworek T, Xu H, Gaynor BJ, et al.Contribution of common genetic variants to risk of early onset ischemic stroke.Neurology. Published online August 31, 2022. doi:10.1212/wnl.0000000000201006American Red Cross.Facts about blood and blood types.

Jaworek T, Xu H, Gaynor BJ, et al.Contribution of common genetic variants to risk of early onset ischemic stroke.Neurology. Published online August 31, 2022. doi:10.1212/wnl.0000000000201006

American Red Cross.Facts about blood and blood types.

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