Among the four major ABO blood types—A, B, AB, and O—people with blood type O have generally shown lower rates of some cancers in large observational studies, particularly pancreatic cancer and stomach (gastric) cancer.
But there is an important distinction: blood type O does not make someone immune to cancer, and it does not mean people with other blood types will develop cancer.
Blood type is only one biological characteristic among many, and the differences observed in research are generally modest compared with established cancer risk factors such as smoking, obesity, alcohol use, infections, age, family history, and environmental exposures.
So, Which Blood Type Has the Lowest Cancer Risk?
If we’re talking about the ABO blood types and associations observed across multiple cancer studies, blood type O is the one most consistently linked with lower risk for certain cancers.
A large systematic review and meta-analysis involving 89 studies and more than 100,000 cancer cases found that blood group O was associated with lower overall cancer risk compared with non-O groups. It also found particularly notable associations with pancreatic and gastric cancers.
A much larger 2023 meta-analysis examined 127 publications involving approximately 20 million participants and found associations between ABO blood groups and several cancers. The strongest evidence for blood type O being associated with lower risk involved certain digestive cancers, especially pancreatic cancer.
However, these are associations—not proof that blood type itself causes or prevents cancer.
1. Blood Type O and Pancreatic Cancer
One of the clearest findings concerns pancreatic cancer.
In a large prospective study involving more than 107,000 people, researchers found that people with blood types A, B, or AB had higher rates of pancreatic cancer compared with people with blood type O.
Compared with blood type O, the adjusted hazard ratios were:
- Type A: 1.32
- Type AB: 1.51
- Type B: 1.72
The researchers estimated that a portion of pancreatic cancer cases in that population was associated with inheriting a non-O blood group.
This doesn’t mean that someone with type B, for example, has a high probability of developing pancreatic cancer.
It means that at a population level, the observed risk was higher than in people with type O.
That’s an important difference.
2. Blood Type O and Stomach Cancer
The relationship also appears in gastric (stomach) cancer.
Researchers have repeatedly observed that blood group A is associated with a somewhat higher risk of gastric cancer, while blood group O tends to be associated with a somewhat lower risk.
A systematic review and genetic study involving more than 2.4 million controls found that blood groups A and AB were associated with increased gastric cancer risk compared with type O.
Another meta-analysis found that type O was associated with a modestly reduced risk of gastric cancer compared with non-O blood groups.
Researchers have proposed several possible explanations, including relationships between ABO blood-group antigens, inflammation, cell adhesion, immune responses, and infections such as Helicobacter pylori.
But the exact biological mechanism remains an area of research.
3. What About Blood Type A?
Blood type A has received considerable attention because several studies have found associations with increased risk for particular cancers.
The strongest and most consistently reported associations include:
- Gastric cancer
- Pancreatic cancer
A large meta-analysis found that blood group A was associated with increased risk of several cancers, including stomach, pancreatic, colorectal, liver, breast, ovarian, cervical, bladder, oral cavity, and nasopharyngeal cancers.
But again, “higher relative risk” does not mean “you will get cancer.”
Cancer is multifactorial. A blood type association may change statistical risk without being a dominant factor in an individual’s health.
4. What About Blood Types B and AB?
Blood types B and AB have also been studied.
Some research has found associations between these blood groups and particular cancers, particularly cancers of the digestive system.
For example, the large 2023 meta-analysis reported associations involving:
- AB: stomach, pancreatic, and ovarian cancers
- B: pancreatic and esophageal cancers, among others
However, the strength and consistency of these associations vary by cancer type and population.
This is why it isn’t scientifically accurate to create a simple ranking such as:
O → B → A → AB
and call that a ranking of cancer risk.
Cancer risk doesn’t work that way.
Different blood types may be associated with different cancers in different directions.
Why Could Blood Type Affect Cancer Risk?
Scientists are still investigating this question.
Your ABO blood type is determined by inherited genes that influence molecules called ABO blood-group antigens.
These molecules aren’t simply labels found on your red blood cells. Related structures can occur on other cells and tissues and may interact with biological processes involved in:
- Cell adhesion
- Inflammation
- Immune responses
- Blood clotting
- Infection
- Tumor-cell behavior
One possibility is that ABO-related biological differences could influence how certain cancers develop or interact with surrounding tissues.
But these mechanisms remain under investigation.
The important takeaway is that researchers have identified statistical associations, not a simple explanation such as “type O prevents cancer.”
Does Blood Type O Protect You From Cancer?
No.
This is perhaps the most important point.
Having type O doesn’t mean you are protected from cancer.
A person with blood type O can still develop:
- Lung cancer
- Breast cancer
- Colorectal cancer
- Prostate cancer
- Skin cancer
- Pancreatic cancer
- Stomach cancer
- Blood cancers
- Many other cancers
Likewise, someone with blood type A, B, or AB may never develop cancer.
Blood type is not a cancer screening test.
Your Blood Type Doesn’t Determine Your Cancer Destiny
It’s easy to see headlines about blood type and cancer and assume that genetics has already determined your future.
It hasn’t.
There are many established and potentially modifiable factors that have a much more practical role in cancer prevention.
These include:
Don’t smoke
Tobacco exposure is a major preventable cause of cancer.
Maintain a healthy weight
Excess body weight is associated with increased risk for several cancers.
Limit alcohol
Alcohol consumption is associated with several types of cancer, and risk generally increases with greater exposure.
Stay physically active
Regular physical activity is associated with lower risk of several cancers.
Eat a balanced diet
Emphasize vegetables, fruits, whole grains, legumes, and other minimally processed foods while limiting highly processed foods and excess calories.
Keep up with recommended screening
Depending on your age, sex, family history, and other risk factors, screening can help detect certain cancers—or precancerous changes—before they become advanced.
These actions are considerably more useful than worrying about whether your blood type is A, B, AB, or O.
Can You Change Your Cancer Risk If You Have Type A, B, or AB?
Absolutely.
Your ABO blood type cannot be changed through diet, exercise, supplements, or medication.
But your overall cancer risk is influenced by many factors that can be addressed.
For example, someone with type A who doesn’t smoke, maintains a healthy weight, limits alcohol, follows recommended screening, gets appropriate vaccinations, and manages other health risks may have a very different overall cancer-risk profile from someone with the same blood type who has multiple major risk factors.
Blood type is one piece of biology—not a prediction of an individual’s future.
What About Cancer Screening?
This is where the blood-type discussion becomes especially important.
Knowing your blood type should never replace appropriate cancer screening.
Depending on your age and individual risk factors, screening may include tests for cancers such as:
- Colorectal cancer
- Breast cancer
- Cervical cancer
- Lung cancer
- Prostate cancer in appropriate circumstances
People with a strong family history or known inherited cancer syndromes may need a different screening approach.
If you’re concerned about cancer because of your family history or symptoms, discuss your individual risk with a healthcare professional rather than relying on blood type.
A Surprising Detail: Blood Type May Matter Beyond Cancer
ABO blood type has been studied in relation to several health outcomes beyond cancer.
The relationship between blood groups and disease is complex, and researchers have reported associations involving cardiovascular, infectious, and other conditions.
But an association doesn’t necessarily mean that the blood type directly causes the condition.
A 2024 umbrella review of systematic reviews found that although many ABO-related associations were statistically significant, the strength and consistency of evidence varied considerably across outcomes.
This is another reason to be cautious about headlines claiming that one blood type is universally “healthier.”
What the Research Really Says
Here’s the simplest way to understand the evidence:
| Blood Type | What Research Suggests |
|---|---|
| O | Often associated with lower risk of pancreatic and gastric cancer compared with non-O groups |
| A | Associated with higher risk of several cancers, particularly gastric and pancreatic cancer |
| B | Associations reported for some cancers, including pancreatic and esophageal cancer |
| AB | Associations reported for some cancers, including gastric and pancreatic cancer |
These are population-level associations, not individual predictions.
The Bottom Line
Blood type O is the blood group most consistently associated with a lower risk of certain cancers, particularly pancreatic and stomach cancer.
But calling type O the blood type with the “lowest cancer risk” without qualification is too broad.
The research does not show that type O prevents cancer, and it does not mean that people with A, B, or AB blood types should expect to develop cancer.
Your blood type is inherited and cannot be changed. What you can influence are many of the factors that have a much larger practical role in cancer prevention: not smoking, maintaining a healthy weight, staying active, limiting alcohol, eating a balanced diet, protecting yourself from relevant infections, and following recommended cancer screening.