A person’s blood type appears to be linked to their risk of having a stroke before the age of 60, according to a huge meta-analysis by the University of Maryland School of Medicine. The new study indicates that type people who suffered from an early stroke were more slightly likely to have blood type A and less likely to have blood type O, the most common blood type.
The research was published today in the journal Neurology. The elevated risk of early stroke among people with blood type A is only marginal and not a huge cause for concern. That said, the researchers hope their work could someday be used to help prevent strokes in younger adults.
“This study raises an important question that requires a deeper investigation into how our genetically predetermined blood type may play a role in early stroke risk,” Mark T Gladwin, the John Z. and Akiko K. Bowers Distinguished Professor and Dean at the University of Maryland School of Medicine, said in a statement. “It points to the urgent need to find new ways to prevent these potentially devastating events in younger adults.”
The team carried out a meta-analysis of 48 previous studies on genetics and ischemic stroke in people aged 18 to 59 years old, involving a total of 17,000 stroke patients and nearly 600,000 healthy people who never had a stroke. This included people from North America, Europe, Japan, Pakistan, and Australia.
When looking at genetic variations that were linked with a higher risk of early strokes, they found some of the strongest links in the genes that determine blood type.
After adjusting for sex and other factors that may affect the risk, they that people with blood type A had an 18 percent higher risk of having an early stroke than people with other blood types, while people with blood type O had a 12 percent lower risk of having a stroke.
However, this relationship wasn’t found when they looked at late-onset strokes after the age of 60. Instead, they found both early and late-onset strokes were more likely to have blood type B compared to others.
To simplify, there are four main blood groups – A, B, AB, and O – and two antigens present in the blood – A and B – determine a person's blood group: blood type A has A, blood type B has B, blood type AB has both, and blood type O has neither.
The researchers say the nature of this link between early strokes and blood group A is not yet fully understood. However, they suspect it may have something to do with the development of blood clots that their effect on ischemic strokes, caused by a blockage of blood flow to the brain.
This is because other studies have highlighted that people with blood types A and B may have higher risks of developing dangerous blood clots compared to people who have type O blood.
It's thought that blood type may impact health in a number of ways. For instance, a number of studies over the pandemic have found that people with blood type A may be more vulnerable to falling seriously ill with COVID-19. Once again, the nature of that link was uncertain and more evidence before any solid conclusions can be made.
In yet another intriguing link, the latest study also found that blood types A and B are also linked to a heightened risk of deep vein thrombosis, a medical condition that occurs when a blood clot forms in a deep vein.
“We still don’t know why blood type A would confer a higher risk, 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,” explained Steven J. Kittner, study co-principal investigator and Professor of Neurology at the University of Maryland School of Medicine.