🧬 What Does the Research Show?

One systematic review examining studies of ABO blood groups and cancer found a broad pattern in which blood group A was associated with increased cancer risk, while blood group O was associated with decreased risk.

Large cohort research has also found differences depending on the type of cancer.

For example, a study involving more than 339,000 people found that non-O blood types—A, B, and AB—were associated with higher pancreatic cancer risk compared with blood type O. Blood type A was also associated with stomach cancer risk.

These findings are particularly interesting because pancreatic and stomach cancers have been among the cancers most consistently investigated in relation to ABO blood type.

🧪 Blood Type O and Pancreatic Cancer

One of the strongest examples involves pancreatic cancer.

Researchers have repeatedly observed that people with blood type O tend to have a lower risk of pancreatic cancer than people with A, B, or AB blood types.

A major Harvard analysis previously reported that, compared with type O, pancreatic cancer risk was higher among people with type A, B, and AB blood.

This does not mean that type O eliminates the risk.

It simply means that, at the population level, researchers have observed a statistical association.

A person with type O blood can still develop pancreatic cancer, while someone with type A, B, or AB blood may never develop it.

🍽️ What About Stomach Cancer?

The relationship between blood type and stomach cancer has also attracted considerable attention.

Several studies have found that type A blood is associated with a higher risk of stomach cancer compared with type O.

Researchers have proposed several possible explanations, including interactions between blood-group biology, inflammation, and infections such as Helicobacter pylori, a bacterium strongly associated with stomach cancer.

But again, blood type is only one potential factor among many.

Diet, smoking, alcohol consumption, obesity, chronic inflammation, H. pylori infection, genetics, and age can all influence cancer risk.