“The number of people with early strokes is rising,” said the study’s co-principal investigator Steven J. Kittner, MD, MPH, in a press release. Dr. Kittner is a professor of neurology at the University of Maryland School of Medicine (UMSOM) in Baltimore. “These people are more likely to die from the life-threatening event, and survivors potentially face decades with disability. Despite this, there is little research on the causes of early strokes.” It’s estimated 10 to 15 percent of strokes occur in people under age 50, according to a paper published in the February 2020 issue of the journal Stroke.
Early Onset Stroke More Likely in People With Type A Blood
To investigate how genetic factors could influence the risk of stroke, researchers analyzed 48 studies on genetics and ischemic stroke, which included 16,700 stroke patients and 599,237 healthy controls who had never experienced a stroke. They found a link between early-onset stroke — occurring before age 60 — and the area of the chromosome that includes the gene that determines whether a blood type is A, AB, B, or O. The study found that people who experienced an early stroke were more likely to have blood type A and less likely to have blood type O than people with late stroke and people who never had a stroke. Those who had both early and late stroke were also more likely to have blood type B than the healthy control group. After adjusting for sex and other factors, researchers found that those with blood type A had a 16 percent higher risk of early stroke than people with other blood types, and those who had blood type O had a 12 percent lower risk of stroke than people with other blood types. The association of blood type with later-onset stroke was much weaker than blood type’s association with early stroke, according to the authors. This an interesting study, says Brandon Giglio, MD, the director of vascular neurology at NYU Langone Hospital in Brooklyn, New York, who was not involved in the study. “There’s been research to suggest there was also an association between blood type and other clotting disorders, like clots in the legs such as a deep vein thrombosis and of the pulmonary artery — a pulmonary embolism,” he says. A study published in January 2020 in the American Heart Association journal Arteriosclerosis, Thrombosis, and Vascular Biology compared people with type O blood and those with type A or B blood and found the latter were 51 percent more likely to develop deep vein thrombosis and 47 percent more likely to develop a pulmonary embolism. “It’s interesting that this association extends to these types of clots, which are in arteries as opposed to those other clots which are in veins, though different mechanisms and processes cause strokes than those other types of clots,” says Dr. Giglio. The findings suggest there’s probably a connection between the patient’s blood type and the way their body promotes the formation of a clot, he adds.
Blood Types 101
Blood types are determined by the presence or absence of certain antigens, which are substances that can trigger an immune response to foreign “invaders.”
Type O blood (positive and negative) is the most common type of blood in the United States. About 45 percent of white people, 51 percent of Black people, 40 percent of Asians and 57 percent of Hispanics are type O, according to the American Red Cross.
Type A blood is found in 40 percent of white people, 26 percent of Black people, 27.5 percent of Asians, and 31 percent of Hispanics.
Type B blood is found in 11 percent of white people, 19 percent of Black people, 25.4 percent of Asians, and 10 percent of Hispanics.
Type AB blood (meaning it has both A and B antigens) is the rarest type of blood and is found in 4 percent of white people, 3.3 percent of Black people, 7.1 percent of Asians, and 2.2 percent of Hispanics.
Extra Screening for Stroke Due to Blood Type Isn’t Necessary
The researchers emphasized that the increased risk was very modest and that people with type A blood should not worry about having an early-onset stroke or engage in extra screening or medical testing based on this finding. Giglio agrees, saying, “With the information we have at present, I don’t think we have any interventions to modify risk based on the blood type,” he says.
What You Can Do to Reduce Your Risk of Stroke
No matter what blood type you have, there is clear evidence for ways to reduce your risk of stroke, says Giglio. The CDC recommends the following healthy lifestyle choices.
Adopt a healthy diet that’s low in saturated fats, trans fat, and cholesterol and includes lots of fruits and vegetables.Maintain a healthy weight.Follow guidelines for physical activity and get at least 2 hours and 30 minutes of moderate-intensity exercise every week.Don’t smoke and limit alcohol.Pay attention to vascular risk factors such as cholesterol levels, blood pressure, and diabetes.
Researchers Hope These Findings Will Lead to Ways to Prevent Strokes in Younger Adults
“We clearly need more follow-up studies to clarify the mechanisms of increased stroke risk,” says Kittner. The authors also acknowledge that the current study is limited by a “relative lack of diversity among participants.” “Future research may look to see if there are associations between blood types and risk factors for strokes,” says Giglio. It could be that having a certain blood type puts people at risk for a disease that in turn puts them at higher risk of stroke, such as diabetes or obesity, he adds.
