Blood Type and Stroke Risk: New Insights

It may surprise you, but your blood type might actually play a role in your health. Recent research indicates a noteworthy connection between blood type and the risk of experiencing a stroke.

Specifically, individuals with type A blood appear to face an increased risk of having a stroke before reaching the age of 60. This finding comes from a 2022 study that sheds light on how our biological characteristics influence health outcomes.

“This significant and unexpected research finding enhances our understanding of non-modifiable stroke risk factors like blood type,” noted Mark Gladwin, a physician-scientist at the University of Maryland, when the study was released.

While you’re probably familiar with blood types such as A, B, AB, and O—defined by antigens on red blood cells—there are minor variations within these categories due to genetic mutations.

The researchers conducted an analysis of data from 48 genetic studies, including roughly 17,000 stroke patients and close to 600,000 controls, all aged between 18 and 59.

Their study revealed a notable relationship between the gene linked to the A1 blood subgroup and the occurrence of early-onset strokes.

Steven Kittner, a vascular neurologist and senior author from the University of Maryland, remarked, “The incidence of early strokes is rising. These individuals have a higher likelihood of dying from the event, and those who survive might face long-term disabilities. Yet, research on early stroke causes remains scarce.”

A genome-wide search uncovered two regions associated with an earlier stroke risk, one of which corresponds to where blood type genes are located.

Further analysis revealed that people with a gene coding for a variant of blood type A have a 16% higher chance of having a stroke before age 60, compared to other blood types. In contrast, those with O1 blood had a 12% lower risk.

However, the researchers cautioned that the increased risk for blood type A is relatively small, meaning extra precautions or screenings aren’t necessarily required.

“We still don’t understand why type A blood might lead to a higher risk,” Kittner pointed out, adding that it likely involves blood-clotting factors such as platelets and certain proteins that influence clot formation.

While the results may seem a bit alarming, it’s important to view them within context. In the U.S., nearly 800,000 strokes occur each year, with the majority—about three in four—happening in individuals aged 65 and older. The risk of stroke doubles every decade after age 55.

Moreover, the study’s participants mainly came from North America, Europe, Japan, Pakistan, and Australia, with underrepresentation of those of non-European ancestry. More diverse studies could provide deeper insights into these findings.

“We definitely need more follow-up research to understand the mechanisms behind this increased stroke risk,” Kittner said.

The study also compared individuals who had strokes before and after age 60. They used a dataset of around 9,300 people over 60 who had strokes and about 25,000 controls in the same age group who did not.

Interestingly, the increased risk associated with type A blood disappeared for the later-onset stroke group, which suggests that the underlying mechanisms for early and late strokes may differ.

Strokes occurring in younger populations are less likely due to atherosclerosis (the buildup of fatty deposits in arteries) and more likely connected to clot formation, according to the authors.

Additionally, the study found that individuals with type B blood had an 11% greater likelihood of experiencing a stroke compared to controls, irrespective of age.

Earlier research indicates that the region of the genome related to blood type—the ‘ABO locus’—is linked to coronary artery calcification, a contributor to heart attacks, and a slightly higher risk of venous thrombosis.

This article is based on research published in Neurology.