Researchers show which blood group has the lowest cancer risk

Researchers Show Which Blood Group Has the Lowest Cancer Risk

It may sound surprising, but researchers have been studying the relationship between blood groups and cancer for decades. While blood type is best known for its importance in blood transfusions and pregnancy care, scientists have discovered that the ABO blood group system may also be associated with the risk of developing certain diseases, including some types of cancer.

Among the four main ABO blood groups—A, B, AB, and O—blood group O has repeatedly been associated with a lower risk of several cancers, particularly pancreatic and stomach cancer.

However, there is an important distinction to make: having type O blood does not mean that a person is protected from cancer. Instead, researchers have identified statistical associations between blood type and cancer risk. These differences are generally much smaller than the effects of major cancer risk factors such as smoking, obesity, alcohol consumption, infections, age, and inherited genetic mutations.

So, what does the research actually show?

Blood Group O Appears to Have the Lowest Overall Cancer Risk

One of the most comprehensive studies on the subject was a systematic review and meta-analysis that examined 89 studies involving more than 100,000 cancer cases across 30 cancer sites.

The researchers found that people with blood group O had a lower overall cancer risk compared with people who had non-O blood types. The pooled analysis estimated an odds ratio of 0.84 for O versus non-O blood groups, suggesting an approximately 16% lower relative odds in the populations included in the analysis.

The researchers also found that blood group O was associated with lower risks for several individual cancers, including pancreatic, gastric, breast, colorectal, ovarian, esophageal, and nasopharyngeal cancers. 

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At the same time, blood group A was associated with increased risk for several cancers, including stomach and pancreatic cancer.

These findings do not mean that every person with type O has a lower cancer risk than every person with type A, B, or AB. Cancer is a complex disease caused by many interacting factors. Blood type is only one potential factor.

The Strongest Evidence: Pancreatic Cancer

The connection between blood type and pancreatic cancer is among the most consistently observed relationships.

A large prospective study examined more than 107,000 people from two major U.S. health-professional cohorts. During nearly one million person-years of follow-up, researchers identified 316 cases of pancreatic cancer.

Compared with people with blood group O, participants with blood group A had a higher risk of pancreatic cancer, while those with AB and B blood types also had higher risks.

The adjusted hazard ratios were:

In that study, blood group O had the lowest incidence rate among the four groups. 

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Another large genetic analysis supported the association. Researchers found that genetic variants corresponding to blood group O were associated with a protective effect against pancreatic cancer. 

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This is particularly interesting because genetic evidence can help researchers determine whether an observed association may have a biological basis rather than being simply the result of chance.

What About Stomach Cancer?

Stomach cancer is another area where the evidence has been relatively consistent.

Researchers have found that blood group A is associated with a higher risk of stomach cancer compared with blood group O.

A large genetic study involving thousands of gastric cancer cases and controls found that people with blood group A had approximately a 19% higher odds of gastric cancer compared with people with blood group O. Blood group AB was also associated with an elevated risk. 

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An umbrella review that examined evidence from numerous systematic reviews and meta-analyses similarly found that blood group O was associated with a lower risk of gastric cancer compared with non-O blood groups, while blood group A showed a higher risk. 

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This does not mean that having blood type A causes stomach cancer. Instead, researchers believe that differences in blood-group antigens may influence biological processes that could affect cancer development.

A Massive Study Involving 20 Million People

The evidence became even more interesting with a large-scale analysis published in 2023.

Researchers examined 127 publications involving approximately 20 million participants and more than 231,000 cancer patients across 20 cancer types.

They compared blood groups A, B, and AB with blood group O and found associations between non-O blood groups and several cancers.

Blood group A was associated with increased risks of a number of cancers, including cancers of the stomach, pancreas, colorectum, liver, ovary, cervix, bladder, breast, and oral cavity.

Blood group AB was associated with increased risks of stomach, pancreatic, and ovarian cancers. Blood group B was associated with increased risks of pancreatic, cervical, and esophageal cancers in the analysis.

The genetic component of the study also provided evidence that variants associated with blood group O may have a protective relationship with pancreatic cancer. 

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Because the analysis included such a large number of participants, it provides some of the strongest evidence to date that the ABO blood group system is associated with cancer risk.

Why Could Blood Type Affect Cancer Risk?

Scientists are still trying to understand the biological mechanisms behind these associations.

The ABO blood group system is determined by genes that control specific molecules, called antigens, on the surface of red blood cells. However, related molecules can also be present on other cells and tissues throughout the body.

Researchers have proposed several possible explanations for the connection between ABO blood groups and cancer.

One possibility involves inflammation.

Chronic inflammation plays an important role in the development of many diseases, including cancer. Differences in ABO blood-group biology could influence inflammatory processes and immune responses.

Another possibility involves cell adhesion and signaling. Cancer cells need to interact with surrounding tissues, blood vessels, and immune cells as tumors develop and spread. ABO-related molecules could potentially affect some of these interactions.

Blood groups may also influence levels of certain proteins involved in blood clotting and circulation. This could be relevant because abnormal blood clotting and changes in blood vessels are common in cancer patients.

There may also be relationships between ABO blood groups and infections. Certain microorganisms can interact differently with people depending on the molecules present on their cells. Because some infections are associated with cancer, this could provide another indirect pathway.

However, these mechanisms are still being investigated. Researchers cannot currently say that one specific biological pathway completely explains why blood group O appears to have a lower risk of some cancers.

Does Blood Type O Protect Against All Cancer?

No.

This is one of the most important points to understand.

Researchers have found associations between blood type and specific cancers, but the relationship is not uniform across every cancer.

For example, some studies have found associations involving pancreatic and gastric cancers, while evidence for other cancers is weaker or inconsistent.

A large cohort study involving approximately 1.6 million blood donors from Sweden and Denmark found associations between ABO blood groups and cancer at several anatomical sites. However, the researchers emphasized that the most consistent relationships involved cancers of the pancreas and upper gastrointestinal tract. 

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Other research can produce different results depending on the population, cancer type, ethnicity, study design, and other variables.

In fact, an umbrella review of systematic reviews found that many observed associations between blood groups and health outcomes had substantial uncertainty or statistical heterogeneity. This means researchers still need stronger prospective evidence for many of the proposed relationships. 

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Therefore, it would be inaccurate to say:

“Blood type O prevents cancer.”

A more scientifically accurate statement is:

“Blood type O is associated with a lower risk of several cancers in observational research, particularly pancreatic and gastric cancer.”

What About Blood Groups A, B, and AB?

The evidence suggests that some non-O blood groups may be associated with higher risks of particular cancers, but there is no simple ranking that applies to every type of cancer.

Blood group A has received considerable attention because of its association with stomach and pancreatic cancer.

For pancreatic cancer, studies have repeatedly found higher risk among people with A, B, and AB blood types compared with O.

For stomach cancer, blood group A has also been associated with increased risk.

However, B and AB blood groups do not necessarily have the highest risk for every cancer. Different studies have identified different associations.

For example, some research has found that AB may be associated with a lower risk of certain cancers. A 2024 systematic review of head and neck tumors found an association between blood group AB and lower risk in some analyses. The researchers also emphasized that more prospective studies are needed. 

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This illustrates why it is misleading to create a universal “best” and “worst” blood type for cancer.

Does Having Type O Mean You Don't Need Cancer Screening?

Absolutely not.

A person with blood type O can still develop cancer.

Blood type does not replace established cancer-prevention measures or screening recommendations. Someone with type O who smokes, for example, can still have a substantial risk of lung cancer. Similarly, type O does not eliminate the risks associated with obesity, alcohol, certain infections, family history, or age.

Cancer screening should be based on established medical guidelines and individual risk factors—not ABO blood type alone.

The same principle applies to people with A, B, or AB blood types. Having a non-O blood type does not mean that someone will develop cancer.

The differences identified in research are statistical associations across populations, not predictions about an individual person's future.

What Can You Actually Do to Reduce Cancer Risk?

Fortunately, the most important cancer-risk factors are things that can often be addressed regardless of blood type.

Not smoking or quitting tobacco is one of the most important steps a person can take.

Maintaining a healthy weight, staying physically active, eating a balanced diet, limiting alcohol consumption, protecting the skin from excessive ultraviolet exposure, and following recommended vaccination and cancer-screening programs can also contribute to reducing cancer risk.

Family history is another important consideration. Some inherited genetic mutations can substantially increase cancer risk, and people with strong family histories may require earlier or more intensive screening.

In other words, knowing your blood type can be interesting, but it should not distract you from the factors that have a much larger impact on cancer risk.

The Bottom Line

So, which blood group has the lowest cancer risk?

Based on current research, blood group O is the leading answer—but with an important qualification.

Large observational studies and meta-analyses consistently suggest that people with blood group O have a lower risk of several cancers compared with people with non-O blood groups. The strongest and most repeated associations involve pancreatic and gastric cancer. 

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However, blood type is not a cancer shield.

A person's overall cancer risk depends on a much larger combination of factors, including age, genetics, smoking, alcohol use, body weight, physical activity, infections, environmental exposures, and family history.

The research into blood groups is valuable because it may help scientists better understand how inherited biological differences influence cancer development. It could eventually contribute to improved risk prediction or new approaches to prevention and treatment.

For now, though, the message is simple:

Type O may be associated with a lower risk of several cancers, but no blood group makes someone immune to cancer.

Your blood type is one small piece of a much larger picture. The best way to reduce cancer risk remains following evidence-based prevention strategies, knowing your personal r