![\"Diagram](\"https:\/\/www.europesays.com\/us\/wp-content\/uploads\/2025\/06\/MajorBloodTypesChart642.jpg\")
Blood type is partly determined by the ABO blood group antigens present on red blood cells. (InvictaHOG\/Public Domain\/Wikimedia Commons<\/a>)<\/p>\nEven within these major blood types<\/a>, there are subtle variations caused by mutations in the genes involved.<\/p>\n Related: Scientists Identify New Blood Group, And It’s The World’s Rarest<\/a><\/strong><\/p>\n Researchers analyzed data from 48 genetic studies, which included approximately 17,000 stroke patients and nearly 600,000 non-stroke controls. All participants were between the ages of 18 and 59.<\/p>\n Their findings revealed a clear relationship between the gene responsible for the A1 blood subgroup, and early-onset stroke.<\/p>\n A genome-wide search revealed two locations strongly associated with an earlier risk of stroke. One coincided with the spot where genes for blood type sit.<\/p>\n A second analysis of specific types of blood-type gene then found people whose genome coded for a variation of the A group had a 16 percent higher chance of a stroke before the age 60, compared with a population of other blood types.<\/p>\n For those with a gene for group O1, the risk was lower by 12 percent.<\/p>\n The researchers noted, however, that the additional risk of stroke in people with type A blood is small, so there is no need for extra vigilance or screening in this group.<\/p>\n “We still don’t know why blood type A would confer a higher risk,” said<\/a> senior author and vascular neurologist Steven Kittner from the University of Maryland.<\/p>\n “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.”<\/p>\n While the study findings may seem alarming \u2013 that blood type could change early stroke risk \u2013 let’s put these results into context.<\/p>\n Each year in the US just under 800,000 individuals experience a stroke. Most of these events \u2013 around three out of every four<\/a> \u2013 occur in people 65 years and older, with risks doubling every decade after the age of 55.<\/p>\n Also, the people included in the study lived in North America, Europe, Japan, Pakistan, and Australia, with people of non-European ancestry only making up 35 percent of participants. Future studies with a more diverse sample could help clarify the significance of the results.<\/p>\n “We clearly need more follow-up studies to clarify the mechanisms of increased stroke risk,” Kittner said<\/a>.<\/p>\n Another key finding of the study came from comparing people who had a stroke before the age of 60 to those that had a stroke after the age of 60.<\/p>\n For this, the researchers used a dataset of about 9,300 people over the age of 60 who had a stroke, and some 25,000 controls over the age of 60 who didn’t have a stroke.<\/p>\n They found that the increased risk of stroke in the type A blood group became insignificant in the late-onset stroke group, suggesting that strokes that happen early in life may have a different mechanism compared to those that occur later on.<\/p>\n Strokes in younger people are less likely to be caused by a build-up of fatty deposits in the arteries (a process called atherosclerosis) and more likely to be caused by factors to do with clot formation, the authors said<\/a>.<\/p>\n The study also found that people with type B blood were around 11 percent more likely to have a stroke compared to non-stroke controls regardless of their age.<\/p>\n![\"YouTube](\"https:\/\/upload.wikimedia.org\/wikipedia\/commons\/3\/32\/ABO_blood_type.svg\")
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