Your Blood Type May Raise Your Risk of an Early Stroke—But Only a Little

Bag of Type B Blood

Mr.Nuttakorn Chaiwetchakan / EyeEm / Getty Images

Key Features

  • A new meta-analysis of research shows that your blood type might have a very small effect on your risk for a stroke.
  • Researchers think blood type could affect stroke risk because it appears to increase blood clotting.
  • Experts say that the tiny amount that your risk of stroke is raised by your blood type is not as important as other stroke risk factors like high blood pressure or smoking. Unlike your blood type, you have some control over making changes to these risk factors.

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 that raise your risk of stroke a lot more.

The finding comes from a recent meta-analysis of 48 studies that looked at genetics and 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.

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.

  • People with type A blood had a 16% higher risk of having an ischemic stroke (the kind caused by a blockage in a blood vessel) before age 60
  • People with type O blood had a 12% lower risk of having a stroke at any age
  • People with blood type B had a slightly increased risk of a stroke at any age

How Does Blood Typing Work?

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 B antigens:

  • Type A blood has A antigens (about 40% of people have this type)
  • Type B blood has B antigens (about 10% of people have this type)
  • Type AB has both antigens (about 5% of people have this type)
  • Type O blood has neither antigen (about 45% of people have this type)

Rh Factor

Each blood type can be also either RH positive or negative, which means that a protein called Rhesus 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 to Braxton 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 increase blood clotting.

In the meta-analysis, the researchers also looked at whether blood type affected the incidence of blood clots that form in veins (venous thromboembolism or 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.”

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. When many studies have 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 anyone
  • Type AB blood (both A and B antigens) can receive any type of blood

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 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.

2 Sources
Verywell Health uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read our editorial process to learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.
  1. Jaworek T, Xu H, Gaynor BJ, et al. Contribution of common genetic variants to risk of early onset ischemic strokeNeurology. Published online August 31, 2022. doi:10.1212/wnl.0000000000201006

  2. American Red Cross. Facts about blood and blood types.

By Valerie DeBenedette
Valerie DeBenedette has over 30 years' experience writing about health and medicine. She is the former managing editor of Drug Topics magazine.