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Friday, September 9, 2022

Your Blood Type May Influence Your Stroke Risk, Study Shows

September 9, 2022
By Jocelyn Solis-Moreira

Nurse Hooking Up A Woman for Blood Donation
Nurse Hooking Up A Woman for Blood Donation. Photo: Getty

Your blood type can tell you many things about yourself, such as your risk for certain health conditions, your risk for blood clots and even whether you may be prone to kidney stones. Now there's evidence that your blood type may also predict one's risk for experiencing a stroke.

Newly published research in the journal Neurology shows a strong association between having blood type A and an increased risk of early-onset ischemic stroke before the age of 60.

Stroke is one of the leading causes of death in the United States, according to the Centers for Disease Control and Prevention (CDC), whose data shows that someone experiences a stroke every 40 seconds and dies from one every 3.5 minutes. Nearly 90% of all strokes are ischemic strokes, which is when a blood clot stops blood from reaching the brain.

While the new study suggests there's a strong genetic factor linking blood type to stroke, the study's co-author Braxton Mitchell, PhD, MPH, a genetic epidemiologist at the University of Maryland School of Medicine told Health that you shouldn't worry too much about your blood group.

"In the grand scheme of things, it's a smaller risk factor than others," Mitchell said, explaining that blood type is one of many genetic and environmental factors that increase a person's risk of stroke.

Here's a closer look at how big (or small) of a role your blood type plays.

Type A Blood Group Showed Strongest Link to Early Onset Stroke

Researchers involved in the new study sought to understand how important genetics are when it comes to a person's risk of stroke. To do that, they conducted a genome-wide association study that included collecting data on stroke cases from around the world. A majority of the study data was from the United States and Europe.

From 48 different studies, researchers analyzed health information associated with nearly 17,000 individual stroke patients whose ages ranged from 18 to 59 years old. More 599,237 medical cases not involving stroke acted as controls. People were divided by the four main blood groups based upon whether they had an early stroke, late stroke, or no stroke.

Researchers looked for genetic variants across the genome and between the study groups. They found significant genetic differences between patients who had experienced a stroke and those who had not. The differences were observed specifically in the genes coding for the ABO blood group.

"It was surprising to me that the ABO blood group was by far the strongest association that we saw in early-onset stroke," explains Dr. Mitchell. "And not only that, the association was much stronger for early-onset stroke than it was for late-onset stroke. So that was a surprise for us."

Having type A blood was associated with an 18% greater chance of developing early-onset stroke. This included a greater risk of developing blood clots, which can trigger a stroke. In contrast, people with blood type O were 12% less likely to have an early stroke than other blood types.

There was also a slight risk of both early and late stroke in people with type B blood. However, after the researchers adjusted for sex and other contributing factors of stroke, the association was gone.

Findings May Be Catalyst for Those at Risk

Sandra Narayanan, MD, a vascular neurologist and neurointerventional surgeon at Pacific Neuroscience Institute, who was not involved in the study, told Health that the research adds to what scientists already know about uncontrollable risk factors for heart disease—such as the genetics that contribute to a person's blood type.

However, Narayanan added that the findings may be the catalyst that people with a riskier genetic profile for stroke need to make healthier lifestyle changes.

From a medical standpoint, Dr. Narayanan added that understanding the genetic basis behind stroke could "initiate the conversation regarding medications or other strategies to reduce arterial or venous thrombosis."

Because only 35% of participants were not European, she adds that future studies with more diverse populations may help to better understand stroke risks across blood types of different races and ethnicities.

Additional Stroke Risk Factors

Along with genetics and blood type, age is another factor that can elevate your risk of stroke. The CDC warns that after age 55, your stroke risk doubles every decade. While strokes happen most often among people 65 years and older, one in seven strokes happen in those between 15 and 49.

A person's sex can also influence stroke. A 2022 review reports that women more than men are more likely to have a stroke and a disproportionate burden of disability and death afterward.

A separate 2022 study calculated that young women between 35 to 45 faced a 44% greater risk of ischemic stroke than men of the same age. The CDC explains that women tend to be in more danger of having a stroke because of pregnancy and using birth control pills.

Amongst all races and ethnicities, Black individuals have the greatest stroke risk. The American Heart Association says one of the reasons Black Americans have a higher prevalence of stroke is because two-thirds of this racial group tend to have at least one risk factor for stroke, including:

  • Diabetes
  • Sickle cell anemia
  • High blood pressure
  • High cholesterol
  • Obesity or being overweight

What's more, a 2021 CDC study suggests that Black Americans have the worst outcomes. Black men, most of all, faced the greatest risk of stroke death and the lowest 5-year survival rate.

However, Dr. Mitchell said that there are much more influential components than the uncontrollable risk factors mentioned above. "It's a somewhat rare event," he adds. "I would tell people that if you really worried about your risk of stroke, I would look at your other risk factors and try to get them under control."

Preventative Measures

This may be surprising, but about 80% of strokes are preventable, said Dr. Narayanan. To prevent a stroke from happening in the first place or reduce your risk of it happening again, she recommends these strategies for maintaining a healthy lifestyle. These include:

  • Quit smoking or not smoking altogether.
  • Keep a blood pressure machine at home if you have high blood pressure and keep track of your measurements everyday. Dr. Narayanan says to bring these numbers with you or the log to your doctor's appointments. "Goal BP is <140/90 mm Hg (or <130/80 mm Hg for patients with diabetes mellitus)."
  • Eat a Mediterranean-style diet rich in fruits, vegetables, whole grains, fish, and nuts.
  • Exercise. Research suggests that exercising for at least 2½ hours per week for 3 months after a stroke boosted a person's health and overall quality of life. Dr. Narayanan says that even moving around for 10 minutes daily makes a bigger difference than not doing anything.
  • Know your cholesterol. "If you've already had a stroke or [transient ischemic attack], aim for low-density lipoprotein (LDL of <70 mg/dL)."

"Consistency is key to maintaining healthy lifestyle interventions. Start early. [About] 10-15% of strokes occur in adults less than 50 years of age," advises Dr. Narayanan.

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