Link Between Blood Type and Early Stroke Risk

Recent research indicates a notable connection between blood type and the risk of stroke. Specifically, individuals with type A blood face a heightened risk of experiencing a stroke before turning 60.

This finding, shared in 2022, adds to our understanding of how our biological characteristics can influence health outcomes.

Most people are familiar with the A, B, AB, and O blood types, which are based on specific antigens present on red blood cells.

Within these main blood types, there are, interestingly, variations caused by gene mutations.

Researchers examined data from 48 genetic studies, encompassing around 17,000 stroke patients and nearly 600,000 individuals without strokes. All subjects were aged 18 to 59.

The results displayed a distinct correlation between a gene linked to the A1 blood subgroup and early strokes.

A broader search of the genome identified two regions associated with a higher risk for early strokes, one being located where blood type genes are situated.

Additionally, a focused analysis of blood-type genes showed that those with a variation of the A group had a 16 percent greater likelihood of a stroke before age 60, compared to individuals with other blood types. Conversely, those with the O1 gene had a 12 percent lower risk.

However, researchers noted that the increased stroke risk for type A blood is relatively minor, and there’s no need for heightened monitoring for this group.

“We still don’t know why blood type A might be linked to a higher risk,” mentioned Steven Kittner, a vascular neurologist at the University of Maryland. “It likely relates to blood-clotting factors like platelets and vessel-lining cells, among other proteins involved in blood clot formation.”

While these findings might sound concerning, it’s important to consider context. In the U.S., nearly 800,000 people experience strokes annually. The majority of these occur in individuals aged 65 and older, with the risk of stroke doubling every decade after 55.

The participants in the study were primarily from North America, Europe, Japan, Pakistan, and Australia, with individuals of non-European descent making up only 35 percent of the total. Future research with a more diverse group could clarify the findings’ relevance.

“We clearly need more follow-up studies to pinpoint how stroke risk is heightened,” Kittner added.

Another significant insight from the study compared those who had strokes before 60 with those after. Researchers analyzed data from roughly 9,300 individuals over 60 who had a stroke and about 25,000 controls. The increased risk associated with type A blood was found to be insignificant in older stroke patients, suggesting that strokes at different life stages might involve different underlying mechanisms.

Strokes in younger individuals are less likely tied to a buildup of fatty deposits (atherosclerosis) and more related to clot formation, as indicated by the researchers.

The study also revealed that individuals with type B blood were about 11 percent more likely to suffer a stroke compared to non-stroke counterparts, regardless of age.

Past research suggests that the genetic region responsible for blood type, known as the ‘ABO locus,’ may be associated with coronary artery calcification and heart attacks. The genetic profiles for blood types A and B have also been linked to a slightly increased risk of venous thrombosis, which involves blood clots forming in veins.

This research was published in Neurology.

An earlier version of this article was published in September 2022.