Blood Types: What Do They Mean For Your Health?
Blood tests are commonly taken to help doctors determine their patients’ overall health. Now, findings from studies show that blood types may also play a role in identifying certain health conditions.
New research suggests that people with blood types A and B are more likely to develop blood clots and have heart attacks and strokes. Researchers say that including blood types in health management plans may help doctors know how to treat their patients best.
It’s also important for patients to know their blood type. In an online survey of 2,000 U.S. adults, 66 percent of participants said they knew their horoscope sign, 58 percent said they knew their credit score, but only 51 percent knew their blood type, while 20 percent knew their cholesterol level. The survey was published in January by Quest Diagnostics, a medical laboratory company.
According to the American Red Cross, there are four main blood types: A, B, O, and AB. Your genes determine your blood type.
Along with these blood groups is a protein found on the surface of red blood cells known as the Rh factor. The American Red Cross says the Rh factor indicates whether the blood of two different people is compatible when mixed. This is especially important when it comes to blood donations and transfusions.
Blood cells that do not have this protein are Rh “negative” (-), and blood cells that have it are Rh “positive” (+). So, adding the Rh factor to blood types results in eight blood subtypes: A+, A-, B+, B-, O+, O-, AB+, and AB-.
Of all the blood types, studies have linked blood types A and B with serious health conditions.
Blood Types A and B May Influence Stroke Risk
Research suggests that people with blood types A and B are at a higher risk of developing blood clots and having heart attacks and strokes.
A 2020 study published in Arteriosclerosis, Thrombosis, and Vascular Biology, the American Heart Association’s journal, found that compared to people with type O blood, people with blood types A and B were:
- • 51 percent more likely to develop deep vein thrombosis, which are blood clots in the legs
- • 47 percent more likely to develop a pulmonary embolism, which occurs when a blood clot travels to the lungs.
- • 10 percent more likely to experience heart failure
- • 8 percent more likely to have a heart attack
There is some good news, however. The study showed people with blood types A and B have a 3 percent lower risk of high blood pressure.
There are many possible reasons why people with blood types A and B have these health risks, Dr. Mary Cushman, a hematologist at the University of Vermont (UVM) Medical Center and a professor of medicine and pathology at the Larner College of Medicine at UVM in Burlington, Vermont, said in an interview with AARP.
For one, the enzyme that controls blood type modifies a protein called the “von Willebrand factor,” which helps to form blood clots. The modifications to the protein are different in different blood types, according to Dr. Cushman, who was not involved in the study. For example, people with type O blood have the lowest levels of von Willebrand factor on average and the lowest risk of abnormal clots, she said. Type AB has the highest level and, in some studies, the highest risk of blood clots, she added.
In a separate interview with the American Heart Association, Dr. Cushman said there were limitations to this research. For instance, people with type AB blood were excluded from the study because of the small number of people with this blood type compared to other blood types. Also, there was a lack of cause-and-effect explanations for the findings, especially when it came to how types A and B blood would lower hypertension when it increases cardiovascular disease, she said.
Type A, AB Linked With Other Conditions
There are some studies that link type A blood to higher levels of low-density lipoprotein cholesterol or the “bad” cholesterol, that can cause clogged arteries. In addition, type AB blood has been associated with inflammation, which may adversely affect blood vessels.
Another study by researchers at the University of Maryland School of Medicine (UMSOM) linked type A blood with early-onset stroke, defined as an ischemic stroke (caused by a blood clot that blocks a blood vessel in the brain) occurring before age 60. The UMSOM team reviewed 48 studies on genetics and ischemic stroke that involved 17,000 stroke patients from North America, Europe, Japan, Pakistan, and Australia. The meta-analysis found that people who had blood type A had a 16 percent higher risk of having an early stroke than people with other blood types.
Experts Say Keep Study Findings in Context
UMSOM investigators said that the increased risk for stroke was very modest and people with type A blood should not worry about having an early-onset stroke or having to undergo extra screening or medical testing based on the findings of their study, published in August 2022 in the journal Neurology.
“We clearly need more follow-up studies to clarify the mechanisms of increased stroke risk,” Dr. Steven J. Kittner, Professor of Neurology at UMSOM, said in a news statement.
Dr. Cushman echoed that statement.
“I don’t advise that patients with non-O blood types get distressed over these findings, but that they simply utilize them to consider how they might take better care to prevent cardiovascular diseases,” Dr. Cushman said. “Many of these diseases can be prevented through lifestyle and treatment of hypertension and high cholesterol.”
On the other hand, knowing your blood type may give you added insight into your heart health, and doctors can narrow down patients who may be at high risk for heart disease, Dr. Robert Salazar, a cardiologist at Memorial Hermann Health System in Houston, told AARP.
For these people, Dr. Salazar recommends following the American Heart Association’s “Life’s Essential 8”— the eight essential components of heart health:
• Eat better
• Be more active
• Quit tobacco
• Get healthy sleep
• Manage weight
• Control cholesterol
• Manage blood sugar
• Manage blood pressure
Also, Dr. Cushman said people with type O blood, which is compatible with all blood types, should not have a false sense of security because studies have not linked this blood type to major cardiovascular events.
“If you have an O blood type, you may have a slightly lower risk of some disease like thrombosis, but it doesn’t completely protect you from the risk,” Dr. Cushman told AARP.
If you do not know your blood type, the American Red Cross says you can ask your doctor to do a simple blood test, or you can donate blood to the American Red Cross.