Studies have found that blood type dictates the percentage of risk of having a stroke before the age of 60. Type A blood may be at higher risk in comparison to other blood groups. On the other hand blood type O is at a smaller risk to have an early on-set stroke according to a new meta-analysis.
The study was conducted by a team led by scientists from the University of Maryland School of Medicine in the United States, who researched the link between genetic characteristics such as blood type and their relationship to stroke. To achieve this they analyzed data from 48 genetic studies on ischemic strokes in adults between the ages of 18 and 59. Ischemic strokes are triggered by a blockage of blood flow to the brain. Approximately 17,000 stroke patients and almost 600,000 healthy controls who had never experienced a stroke were studied.
"We were interested in trying to identify the genetic determinants of stroke,” the study’s co-principal investigator Braxton Mitchell told Euro-news Next.
"For stroke, we've known for a long time that there's a big environmental component, but there's also a genetic component," said Mitchell, who is a professor of medicine at the University of Maryland School of Medicine.
To further understand this, he and his colleagues looked across the genetic profiles of people, and found a connection between early-onset stroke and the part of the chromosome that includes the gene that determines a person’s blood type.
Persons inherit their blood group through their parents genes. There are four main blood groups in humans, A, B, AB and O. Blood group O is the most common.
What was identified by researchers is that those with early-onset of stroke were those with blood type A and those having late strokes or none at all were blood type O.
"Having blood type A increases your risk by about 16 per cent for early-onset stroke, but only about 5 percent for later onset stroke," said Mitchell.
"If you have blood type O, you're 12 percent less likely to get an early-onset stroke, compared to only 4 percent less likely to get a later onset stroke".
Increased risk of stroke remains moderate
Although researchers identified a connection between having blood type A and the risk of early-onset stroke, they highlighted that the increased risk was very modest.
They emphasized that persons with type A blood should not be concerned about having an early-onset stroke, or conduct any additional medical testing or screening based on the findings of this study.
"Clinically, we shouldn't be worried about our blood types putting us at high risk for stroke," said Mitchell.
"There are other risk factors for stroke that are much more important, like hypertension and smoking, for example. So if we want to reduce our risk of stroke, those are really the factors that we should be paying attention to".
Additionally, he added: "Having said that, what we wonder about is whether if you have those risk factors, and you also have blood type A, does that make those risk factors even more powerful? We don't know that yet. But that's one of the things that we're looking at".
Researchers are still unsure as to why blood type A carries the higher risk, but they suppose it is related to certain blood clotting factors. Different researches have identified A blood type persons to be at a slightly higher risk of developing blood clots in the legs - known as deep vein thrombosis.
"This sort of pro-clotting background of having blood group A probably puts you at higher risk for clotting-related diseases, of which stroke is one of them," said Mitchell.
An important restriction to the researchers analysis was the lack of diversity among the research participants who were mainly European. A follow-up study is suggested to cover a more diverse population.
"We all have different genetic variants, and genetic variants often tend to cluster within different ancestry groups. So we may be missing some important variants by only looking at a small representation of ancestry groups" said Mitchell.
Blood type linked to risk of other conditions
Links have been found between blood type and risk of developing other medical conditions - other research has suggested that it's not just stroke risk. For instance a Harvard School of Public Health study identified people with blood types A, B, or AB to be at a higher risk for coronary heart disease than blood type O people. It was blood type AB, the rarest type that was at greatest risk. Additionally studies have identified that Blood type A is also at higher risk of stomach cancer in comparison to other blood types. What's important to mention here is that the reason for this relationship between blood type and health conditions remains unknown.
So if you have type A blood, how worried should you be?
Changing your blood type isn't really possible and there are various risk factors that lead to stroke that are caused directly by a person including blood pressure, nicotine habits, alcohol use and amount of exercise.
"I would say, don't be worried at all,” said Mitchell. “I would think about these other modifiable risk factors and focus on those, because they're not only risk factors for stroke, but these are risk factors for heart disease and cancers, and so on".
'Great step' towards helping to reduce stroke risk
In response to the research findings, Clare Jonas from UK charity Stroke Association stated that the results were a "great step" towards better monitoring of risk factors for early stroke.
"The majority of strokes happen to older people, due to reasons we are commonly aware of such as high blood pressure, thickening of the arteries, or atrial fibrillation," said Jonas, who is Research Communications and Engagement Lead at the Stroke Association, which provides support to those who have suffered a stroke.
"The causes of stroke in younger adults aren’t as well understood, which makes them harder to prevent. We don’t yet know why people with blood type A might be at increased risk of early stroke. This means we can’t yet develop targeted prevention for early stroke". she explained in a statement.
"However, this research is a great step towards helping healthcare professionals understand who would most benefit from monitoring for other risk factors and being offered interventions to help reduce the risk," she added.