The Blood Type That Increases Your Risk Of Stroke

Whether we like it or not, we humans are born with many immutable characteristics, some of which are actually quite helpful. Men who happen to be born with a recessive allele, for example, can look forward to keeping their hair as they age. But there are also certain aspects of our inherent physiology that can have some not so desirable effects.

Take for instance, blood type. It's only been in the last 100 or so years that we've come to understand the importance of blood type and how it differs between humans. This particular genetic characteristic is incredibly important when it comes to blood transfusions, for example, as getting the wrong blood type for such a procedure can be fatal. But our blood type can also tell us about potential health risks we might face as we get older.

Blood is grouped into four main types — A, B, AB and O — and these types are determined by the specific antigens which do or don't exist on the surface of our red blood cells. What's more, studies have been carried out to see if specific blood types are correlated with specific health conditions, and so far we've learned quite a lot in that regard. If you have a certain blood type, for instance, you could be at risk for a painful death, while another blood type seems to be correlated with a higher risk of having a stroke before the age of 60.

Among the many worrying health trends out there right now are the rising stroke rates in younger people. A report from the CDC compared two time-frames: 2011–2013 and 2020–2022 and the results showed that strokes had become 8% more prevalent in the latter period with those aged 18 to 44 experiencing 14.6% more strokes and those aged 45 to 64 experiencing 15.7% more. Despite this concerning development, the research on early strokes isn't quite as robust as it could be, but a 2022 meta-analysis suggests that blood type could be linked to people's risk of experiencing a stroke before the age of 60.

The analysis, entitled "Contribution of Common Genetic Variants to Risk of Early-Onset Ischemic Stroke" was published in the journal Neurology and specifically looked at ischemic strokes, which happen as the result of a blockage in a blood vessel to the brain. According to the American Stroke Association, this accounts for about 87% of strokes. Researchers carried out an analysis of genome-wide association studies that looked at early-onset stroke (EOS) in people aged 18 to 59. The team took statistics from 16,730 stroke cases and almost 600,000 non-stroke control cases taken from 48 different studies. They then identified genetic variations that appeared to be linked with a stroke and found a significant association of EOS with the A1 blood type. Specifically, the study found that people with blood type A were at a higher risk (16%) of having a stroke between the ages of 18 and 60 while those with blood type O were at a 12% lower risk.

Despite what appear to be alarming findings, the research team behind this study of early-onset strokes did make sure to stress that people with type A blood should not be too concerned. The increased risk is small enough that there's no extra screening or medical action required, and researchers aren't even sure why blood type A might correlate with a higher risk of EOS. It likely has to do with the way the blood clots, with co-author Dr. Steven Kittner, pointing to platelets, cells lining the blood vessels, and other circulating proteins as likely elements involved in the link. Follow-up studies are now required to better understand why blood type A appears to increase the risk for early stroke.

Still, this is an important first step, especially since the causes of early stroke are nowhere near as well understood as strokes later in life, which are known to be caused by factors such as high blood pressure or thickening of the arteries. Based on this meta-analysis alone, experts won't be able to develop any treatments or preventative measures to deal with EOS, but it does point those experts in the right direction, and certainly makes it slightly easier to determine who should be monitored for EOS.