People with type A blood may have a higher risk of suffering a stroke before the age of 60 compared to those with other blood types, according to a 2022 study published in Neurology. The research, which involved a comprehensive analysis of genetic data, highlights a possible connection between blood type and early-onset ischemic stroke—a type caused by reduced blood flow to the brain.Large-Scale Genetic AnalysisResearchers from around the world compiled and reviewed data from 48 genetic studies, including nearly 17,000 individuals who had experienced a stroke and about 600,000 controls who had not. All participants were between 18 and 59 years of age. By conducting a genome-wide association study (GWAS), they aimed to identify genetic variants linked to early stroke.Their search revealed two genetic regions significantly associated with stroke risk. One of them was located near the genes that determine blood type. A closer analysis showed that people with a genetic variant coding for a subtype of type A blood—specifically the A1 subgroup—had a 16% higher chance of having a stroke before turning 60 compared to those with other blood types.On the other hand, individuals with a gene variant linked to blood group O1 had a 12% lower risk of early-onset stroke.Why Blood Type Might MatterWhile the observed increase in stroke risk for people with blood type A is modest, the finding raises important questions about underlying biological mechanisms.“We still don't know why blood type A would confer a higher risk,” said study co-author Dr. Steven Kittner, a vascular neurologist at the University of Maryland. “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.”Since strokes in younger individuals are less often caused by long-term artery damage like atherosclerosis and more frequently due to clot-related issues, researchers believe that blood type might influence these clotting mechanisms more strongly in early-onset cases.Differences Between Early and Late-Onset StrokeTo explore whether the relationship between blood type and stroke was age-dependent, the team also compared genetic data from another 9,300 people who had a stroke after age 60 with 25,000 older adults without a stroke.Interestingly, they found that the link between blood type A and stroke became statistically insignificant in the older group, suggesting that strokes occurring earlier in life may have a distinct biological pathway.Other FindingsThe study also found that individuals with type B blood had about an 11% increased risk of stroke compared to non-stroke controls, regardless of age.Previous research has already shown that the ABO gene region—responsible for determining blood type—is associated with increased risks of coronary artery disease, heart attacks, and venous thrombosis (blood clots in the veins). These findings further support the idea that blood type may play a role in how the body forms and dissolves clots.It’s worth noting, however, that the participants in this study were primarily of European ancestry, with only 35% from non-European backgrounds. The researchers emphasize the need for more diverse studies to understand the broader implications of blood type on stroke risk across populations.Despite the findings, experts caution against unnecessary alarm. “The increased risk is relatively small, and people with type A blood shouldn’t be overly concerned,” said Kittner. “There’s no recommendation at this point for extra screening or preventive action based on blood type alone.”Still, the research opens the door to further exploration of how inherited traits like blood type could contribute to stroke risk and potentially inform more personalized approaches to prevention and treatment.