Blood type linked to 16% higher risk of an early stroke; Which blood group is at the most risk?

Can your blood type hold the key to your health?

Research suggests it does – and quite extensively so.

A study has found a surprising link between blood type and stroke risk, with people carrying one specific blood type facing a higher likelihood of stroke before age 60.

What does the study say?

A meta-analysis of 48 genetic studies – incorporating nearly 17,000 individuals who suffered ischemic strokes before age 60 (termed “early‑onset stroke”) and almost 600,000 stroke‑free controls – has highlighted a notable association between ABO blood types and early stroke risk. This finding, published in 2022, deepens our understanding of how our unique biological makeup can impact our health.

Let’s dive deeper into the findings.


What are the findings?

The four blood groups – A, B, AB, and O – refer to the various chemical markers, which are known as antigens, and found on the surface of our red blood cells. Even within these major blood types, there are subtle variations caused by mutations in the genes involved.

Researchers analyzed data from 48 genetic studies, which included approximately 17,000 stroke patients and nearly 600,000 non-stroke controls, between the ages of 18 and 59.

The headline finding? Individuals with blood type A face a roughly 16% greater risk, while those with type O enjoy a ~12% lower risk, compared to all other groups. Though modest, this effect is statistically significant and particularly pronounced among younger adults.


To break it down more —

A genome-wide search revealed two locations strongly associated with an earlier risk of stroke. One coincided with the spot where genes for blood type sit. A second analysis of specific types of blood-type genes then found people whose genome coded for a variation of the A group had a 16 percent higher chance of a stroke before the age of 60, compared with a population of other blood types.

As per the researchers, however, the additional risk of stroke in people with type A blood is small, so there is no need for extra vigilance or screening in this group.

Steven Kittner, a senior author and vascular neurologist from the University of Maryland, stated, "We still don't know why blood type A would confer a higher risk," adding, "But it likely has something to do with blood-clotting factors like platelets and cells that line the blood vessels as well as other circulating proteins, all of which play a role in the development of blood clots."



Which blood group is most at risk?

The picture becomes clearer:

Type A emerges as the highest‑risk group for early ischemic stroke, carrying a 16% increased relative risk before age 60.

Type O, the most common blood group globally, shows a protective effect – a 12% reduction in risk.

Type B and AB show weaker or mixed associations; AB may have some increased risk in certain populations, but the evidence is less consistent.

Thus, blood type A stands out as carrying the highest risk, while type O appears to be most protective in the context of early stroke risk.


Why would blood type influence stroke risk?

The clues lie in blood‑clotting biology:

von Willebrand factor (vWF) and Factor VIII levels: Non‑O blood types generally exhibit higher levels of vWF and factor VIII – both key promoters of clot formation. This pro‑coagulant tendency predisposes individuals to ischemic events.

Genetic linkage near the ABO gene locus: Whole‑genome analysis isolated early‑onset stroke associations to regions that align with the ABO blood‑type gene region.

Thrombotic tendencies in type A: Type A individuals are slightly more prone to deep vein thrombosis (DVT) – evidence that clotting predisposition could be systemically higher.

Despite these clues, definitive mechanisms remain unclear, calling for more targeted research.



Putting things into perspective:

While the study findings may seem alarming – that blood type could change early stroke risk – let's put these results into context.

Each year in the US, just under 800,000 individuals experience a stroke. Most of these events – around three out of every four – occur in people 65 years and older, with risks doubling every decade after the age of 55. For individuals with high blood pressure, diabetes, smoking habits, or obesity, these modifiable factors overshadow the genetic influence: e.g., hypertension can raise stroke risk several times over.

Besides, the people included in the study lived in North America, Europe, Japan, Pakistan, and Australia, with people of non-European ancestry only making up 35% of participants. Future studies with a more diverse sample could help clarify the significance of the results.

Another key finding of the study came from comparing people who had a stroke before the age of 60 to those who had a stroke after the age of 60. For this, the researchers used a dataset of about 9,300 people over the age of 60 who had a stroke, and some 25,000 controls over the age of 60 who didn't have a stroke.

They found that the increased risk of stroke in the type A blood group became insignificant in the late-onset stroke group, suggesting that strokes that happen early in life may have a different mechanism compared to those that occur later on.

Strokes in younger people are less likely to be caused by a build-up of fatty deposits in the arteries (a process called atherosclerosis) and more likely to be caused by factors related to clot formation, the authors said.

Furthermore, a 16% increase for type A isn't equivalent to dramatically elevated odds; it's a modest shift relative to base population risk. The study also found that people with type B blood were around 11% more likely to have a stroke compared to non-stroke controls, regardless of their age.


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