There are two types of stroke. Hemorrhagic stroke occurs when an artery in the brain ruptures and blood flow causes brain cells to die. Ischemic stroke is characterized by an obstruction of an artery. It may be blocked by a blood clot or a fatty deposit. The clogged area is no longer irrigated by blood. Without oxygen supply, the area can then be affected irreversibly. To find out who might be most prone to ischemic stroke before age 60, the University of Maryland conducted a large meta-analysis published in the journal. Their results suggest that there is indeed a difference in risk according to blood type.
“Most strokes occur later in life. Because of this, we chose a cutoff of 60 years for our study in part to include relatively young stroke cases compared to the age at which strokes usually develop.“, explains Dr. Braxton Mitchell, specialist in epidemiology and public health at Science and Future. For this, the team reviewed 48 written studies on the subject, including 17,000 stroke victims as well as 600,000 control patients, who never had an ischemic stroke. All were between 18 and 59 years old.
A more at risk than O
The results showed that there is indeed a difference according to the blood groups. People with type A had a 16% higher risk of early stroke than those with different blood types. People with blood group B had an 11% increased risk of having a stroke. People with type O were 12% less likely to have an early stroke than those with other blood groups. In addition, the link between blood group and the occurrence of a stroke was very marked for early strokes.
But this link was found to be weaker for strokes that occur later in life. The researchers used another data sample of 9,300 people with stroke and 25,000 without stroke, all over the age of 60 this time. It turned out that with age, the link between group A and increased risk no longer appeared significant. Group B still presented a greater risk of 11%, as for patients under 60 years of age.
Why would group A be more at risk than group O before age 60? The team has not, at this time, determined a cause. “However, we believe that blood type predisposes people to clotting“, explains Dr. Mitchell to Science and Future. Excessive blood clotting leads to the appearance of blood clots, responsible for the occurrence of ischemic strokes. “We also find that blood type A is associated with early venous thromboembolism, another bleeding disorder.Another clue that could guide researchers in future work.
No worries if you are group A
The authors of the study are formal: people whose blood type is A should not worry too much. No need to undergo a screening test or special medical examinations. “It is important to emphasize that people with blood type A should not be particularly concerned about their risk of stroke. Blood type is a much weaker risk factor than other modifiable stroke risk factors, such as high blood pressure and smoking. For people who want to reduce their risk of stroke, these are the main factors to consider.”
Regardless of their blood type, taking care of their hypertension and quitting smoking are the two most important ways to deal with the risk of stroke. Specialists also do not exclude that blood group A accentuates the effects of hypertension and smoking on strokes; they highlight the need for further studies to better understand the phenomenon. Note that during a study on Covid-19, group O also appeared to be more protective, while group A presented more risks.