Which blood type has the lowest risk of cancer? The science explained

You may have seen headlines claiming that doctors have identified one blood type with the lowest risk of cancer. There is some scientific evidence linking ABO blood groups (A, B, AB and O) to the risk of certain cancers, but the truth is more nuanced than the headline suggests.

Blood type O is often discussed as being associated with a lower risk of stomach cancer and pancreatic cancer compared with some non-O blood types. However, this does not mean that people with type O have the lowest risk of every cancer, or that they are protected from cancer.

Let’s look at what research actually shows, why blood type might matter, and what you can do to reduce your cancer risk.

1. What does the research say about blood type and cancer?

Your ABO blood group is determined by inherited genes that influence markers on the surface of red blood cells and other cells in the body. Researchers have investigated whether these markers are associated with the development of cancer.

A systematic review and meta-analysis published in 2014 examined 89 studies, covering more than 100,000 cancer cases across 30 cancer sites. It found associations between blood type O and lower rates of several cancers, particularly stomach and pancreatic cancer. Later research has supported some of these findings but has also highlighted inconsistencies.

Here is how to interpret the evidence:

These are research associations, not predictions of what will happen to an individual. The studies do not establish a universal ranking of the four blood types for all cancers.

2. Pancreatic cancer: one of the strongest associations

Pancreatic cancer is one of the best-studied examples of a possible relationship between ABO blood group and cancer risk.

A study published in the Journal of the National Cancer Institute in 2009 followed participants across two large cohorts. Researchers found the following adjusted relative risks compared with blood type O:

What do these percentages mean?

• A 32% higher relative risk does not mean that 32% of people with blood type A will develop pancreatic cancer.

• The study measured the rate of developing cancer over time, not a person’s lifetime probability of developing it.

• Even when relative differences appear substantial, pancreatic cancer remains uncommon in the general population compared with many other diseases.

• The results show an association; they do not prove that the blood type itself directly causes cancer.

Researchers have proposed that genetic differences around the ABO gene may influence cellular processes, inflammation or interactions with certain infections. The precise biological explanation remains incompletely understood.

3. What about stomach cancer?

Stomach cancer is another cancer for which the association with blood type A has been investigated extensively.

A genetic study and meta-analysis published in 2019 included 40 studies, with more than 33,000 stomach cancer cases and over 2.4 million controls. It found that blood type A and AB were associated with modestly higher stomach cancer risk compared with type O.

One possible explanation involves Helicobacter pylori (H. pylori), a bacterium that can infect the stomach lining and is a known risk factor for stomach cancer.

Blood group antigens can influence how certain bacteria interact with cells. Scientists have investigated whether these interactions partly explain the observed differences between blood groups. However, the blood type association cannot be explained by this mechanism alone with certainty.

Important: Blood type O does not prevent H. pylori infection or eliminate the possibility of stomach cancer. Persistent stomach symptoms or a known infection should be discussed with a healthcare professional regardless of blood type.

4. Does blood type O protect against all cancers?

No. This is where many sensational headlines become misleading.

Cancer includes many different diseases, and each can have different causes and risk factors. A genetic characteristic associated with a lower risk of one cancer may have little or no relationship with another.

A 2024 umbrella review of systematic reviews and meta-analyses examined ABO and Rh blood groups across numerous health outcomes. It found that many reported associations had limited or inconsistent evidence, even when some individual findings were statistically significant.

For example:

• Breast cancer: Some earlier pooled analyses found a small association with blood type, but the findings do not establish a reliable protective blood group.

• Colorectal cancer: Some studies have reported differences between blood groups, but the results have not established type O as universally protective.

• Liver cancer and other cancers: Findings vary between studies and populations.

The overall scientific conclusion is that blood type may be one small piece of a complex picture, rather than a dependable measure of a person’s cancer risk.

5. Why might blood type affect cancer risk?

Scientists are investigating several possible explanations.

These explanations remain areas of research. They should not be interpreted as proof that one blood group has a generally stronger immune system or is inherently better at fighting cancer.

6. What actually helps reduce your risk of cancer?

Compared with relying on blood type, the following actions have much stronger practical value.

The National Cancer Institute identifies tobacco, certain infections, excess body weight and other environmental and lifestyle exposures among important cancer risk factors.

7. Should you worry if your blood type is A, B or AB?

No. Having blood type A, B or AB does not mean you will develop cancer, just as having blood type O does not guarantee that you will avoid it.

Your overall risk depends on many factors, including:

• Age and family history.

• Inherited cancer-related genetic variants.

• Smoking, alcohol consumption and other exposures.

• Certain infections and medical conditions.

• The particular type of cancer being considered.

If several close relatives have had cancer, especially at younger ages, discussing your family history with a doctor may be more useful than focusing on ABO blood type alone.

Final verdict

Blood type O has been associated with lower risk of some cancers, particularly stomach and pancreatic cancer, in several observational studies. But there is no blood type proven to have the lowest risk of every cancer.

Blood type is not a cancer screening test, and there is no need to change your diet, take supplements or seek medical treatment based on your ABO blood group alone.

The most useful approach is to understand your individual risk factors, follow recommended preventive care and seek medical advice for persistent or concerning symptoms.

This information is educational and does not replace individualized medical advice.