A trendy diet left blood type with a hard-to-shake reputation, but respectable research suggests that being A, B, AB, or O may matter — far beyond what you’re eating. (Photo: Getty Images/Kevin Curtis)

A few years back, the Blood Type Diet — a controversial nutritional plan that suggests eating a certain way based on blood type — was all the buzz. The gist, according to the book that popularized the idea, was that doing so could maximize your performance, boost health, protect from disease, build stronger emotions, and even help you live longer. Problem is, last year, the diet was debunked by a study in the journal PLoS ONE, leaving blood type with a bad rep and most people thinking it didn’t matter much beyond the need for a transfusion or donation some day.

But emerging research suggests that while your diet needn’t be so closely linked with your blood, your overall health may be. In fact, one blood type continues to emerge above the rest: blood type O.

Research suggests that people with type O blood are at a lower risk for cardiovascular health issues like stroke and heart attack. A new study from the Karolinska Institute shows that people with type O blood are less likely to die from malaria. Science suggests that people with AB blood are at an increased risk of memory issues down the line compared to people with O blood. And other research pins people with O blood as less likely to experience certain kinds of cancer, like pancreatic and gastric cancers.

This all begs the question: Is type O blood protective?

To answer that, we first have to understand the ABO blood group system: There are four types: A, B, AB, and O (or ABO). Your type is determined by either the presence or absence of antigens on red blood cells, which can trigger an immune response in your body, Kristine Alexander, PhD, a postdoctoral fellow in medicine at the University of Vermont, tells Yahoo Health.

“Blood type A has the A antigen; B has at least one copy of the B antigen; and AB has a copy of A and B. O is when you don’t have either,” she says. “The reason people with blood type O are universal donors is that there is an absence of the A and B antigens — no one’s body is going to form antibodies to attack blood type O.” (If you’re A, and you received type B blood, your body would attack the foreign antibody.)

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Along these same lines, type AB is a universal acceptor — since it has both A and B antigens, people with AB can take in all kinds of blood from the ABO group, but only type O can give to anyone.

“Blood group antigens play different roles in different places of the body. Depending on where they are, they may exert a different effect on different diseases — and depending on the disease, there are different theories,” Arash Etemadi, MD, PhD, a postdoctoral fellow at the National Cancer Institute, tells Yahoo Health.

Scientists don’t yet know all of the proteins or cell types that the ABO enzyme affects, says Alexander. “There could certainly be other, undiscovered ways that blood type influences our physiology.” Here, some of what science knows:

Cardiovascular Perks

Alexander says that it does look as though blood type O is protective in the setting of cardiovascular disease. “There is no reason to think that particular molecules on red blood cells would have anything to do with cardiovascular disease, but those same molecules attach molecules to a protein that is important in blood clotting, called the Von Willebrand factor,” she says. People with type O blood have lower Von Willebrand factor levels. That’s good for the heart because ”it means your blood is a little less likely to clot. And more heart attacks and strokes are caused by blood clots, so anything that can have a part in reducing that risk is beneficial.”

A different study Etemadi conducted looked at mortality rates, and found that people with type O blood lived longer than those with non-O types.

Related: What Your Blood Type Says About Your Life Span

Brain Benefits

What’s good for your heart is usually good for your brain — and a lot of cardiovascular risk factors are also mental health risk factors, says Alexander. “We know that cardiovascular risk factors like high cholesterol and diabetes are also associated with dementia and Alzheimer’s,” says Alexander. But it may also be that the brain benefits linked with type O blood don’t have everything to do with heart health.

Research published in the journal Neurology out of the University of Vermont found that people with type AB blood have an increased risk for cognitive problems as they grow older. Even after taking into account race, sex, and where someone lived, the work found that impaired thinking was 82 percent more likely in people with AB blood than people with A, B, or O blood. Research has also made connections between people with A blood type and obsessive-compulsive disorder.

Blood type could also have an effect on brain functioning through inflammation-related properties. Molecules called soluble E-selectin play an important role in inflammation, due to their involvement in recruiting white blood cells to areas of injury, she says. And no surprise here — they’re also associated with cardiovascular disease, going back to the idea that brain health and heart health are often connected.

Related: Type AB Blood? You May Be More Prone to Memory Loss

Fighting Malaria

It’s thought that type O blood can help tie up an inflammatory response related to malaria, says Etemadi. “Recent research by other groups suggests that it’s more possible in people with A or B blood for malaria parasites to destroy red blood cells. It relies on that blood group antigen that’s only present in A and B,” he says. “Because malaria was a major cause of death a while back, people who were resistant were more likely to live. People with blood type O were more likely to survive in places where malaria was a major cause of death .”

Cutting Cancer Risks

When it comes to cancer, certain blood types are linked to specific kinds. “O blood group has a lower risk of gastric cancer,” says Etemadi. How come? “The main cause of gastric cancer is a microbe; bacteria called H. pylori are among the best known infectious causes of cancer. The reason type A (and possibly B) blood is at increased risk is because of the type of response that your body gives — the inflammatory response is different,” he says. “They are more predisposed to the effect of those bacteria.”



People with blood type O may also be at a lower risk for pancreatic cancer than people with other blood types. But the ‘why’ remains a research mystery, Harvey A. Risch, MD, PhD, a professor of epidemiology at Yale University, tells Yahoo Health. “The reason isn’t known.”

Are There Benefits To AB Blood?

“With most of the current research, it appears there’s not so much of a benefit in non-O blood,” says Etemadi. If you lived in a time or age when bleeding was the main cause of death, things may have been different: Blood O does not have any advantages there — it leads to more bleeding, Etemadi says. But today, cardiovascular issues play a bigger role in death than bleeding.

Some reports have suggested that people with O blood type may be more likely to have depression and intense anxiety, but the science doesn’t always hold. “Most of those studies were done in the 1970s, using small numbers of participants and (currently) outdated mental health diagnostic criteria,” says Alexander. “While intriguing, more research needs to be done to confirm these findings.”

“There have also been some observations that people with blood group O have more stomach ulcers,” says Etemadi. “This is probably not true — it’s just that blood type O bleeds more, and ulcers are more likely to be detected because of that.”

Blood Type Isn’t Everything — Not Even Close

Here’s the important thing to remember: Your blood type — while certainly linked to specific health conditions — doesn’t mean everything. And a doctor probably isn’t going to factor your blood type into your risk for cardiovascular health issues or dementia. “In the future, it could go into establishing risk — but that isn’t commonly done now,” says Alexander.

And while you can’t change yourself from A to O, the effect of blood group on disease risk is “not so definite and not so big,” says Etemadi. “Although in general we thought non-O blood group have a 10 to 12 percent increased risk for cardiovascular disease, you can beat that with changing modifiable risk factors like your weight, diet, and exercise.”

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