Recent research has uncovered an unexpected connection between blood type and the risk of stroke, highlighting that individuals with group A blood may face a greater chance of having a stroke before turning 60.
This revelation, shared in 2022, enriches our insight into how our individual biological traits can influence our health outcomes.
Many are familiar with the A, B, AB, and O blood types—these refer to different antigens present on the surface of our red blood cells.
Yet, within these established blood types, there are nuanced variations stemming from genetic mutations.
Researchers examined data from 48 genetic studies involving about 17,000 stroke patients and nearly 600,000 non-stroke individuals, all aged between 18 and 59.
The research identified a clear link between the gene associated with the A1 blood subgroup and the occurrence of strokes at a younger age.
A broad genomic analysis pinpointed two regions strongly tied to an increased stroke risk. One of these regions corresponded with the genes for blood type.
When analyzing the specific blood-type genes, they discovered that people coded for a variation of the A group had a 16% higher chance of experiencing a stroke before 60 compared to those with other blood types. In contrast, those with group O1 blood had a 12% lower risk.
However, researchers pointed out that the additional stroke risk linked to type A blood is relatively small, indicating a lack of necessity for extra monitoring or screening for this group.
“We’re still uncertain about why blood type A might increase stroke risk,” noted Steven Kittner, a senior author and vascular neurologist at the University of Maryland.
“It probably relates to factors involving blood clotting, like platelets and the cells lining blood vessels, as well as other circulating proteins that contribute to the formation of blood clots.”
While these findings may sound distressing—suggesting that blood type could influence early stroke risk—it’s important to keep them in perspective.
In the U.S., just shy of 800,000 people have a stroke each year, with the majority—around 75%—occurring in individuals aged 65 and older. The risk of stroke doubles every decade after age 55.
Additionally, the study’s participants primarily hailed from North America, Europe, Japan, Pakistan, and Australia, with only 35% being of non-European descent. Future research including a more diverse demographic might help illuminate the study’s implications further.
“We definitely need follow-up studies to better understand the mechanisms that lead to increased stroke risk,” Kittner emphasized.
Another significant insight from the study emerged when comparing individuals who had a stroke before 60 with those who had one later in life.
For this, researchers analyzed a dataset of approximately 9,300 stroke patients aged 60 and above and around 25,000 controls who had not experienced a stroke.
They found that the elevated stroke risk for type A blood became negligible among later-onset stroke patients, implying that strokes occurring earlier might develop through different processes than those occurring later.
Strokes in younger individuals tend to be less related to fatty deposits in arteries (known as atherosclerosis) and more connected to factors that lead to clot formation.
Furthermore, the study indicated that individuals with type B blood are about 11% more likely to have a stroke compared to those who did not have strokes, irrespective of their age.
Previous research suggests that the ABO locus—responsible for blood type—could be tied to conditions like coronary artery calcification and heart attacks.
The genetic sequences for A and B blood types have also been linked with a slightly elevated risk of venous thrombosis, a type of blood clot.
This study was published in Neurology.
A previous version of this article appeared in September 2022.
