Will B12 Deficiency Cause Cancer? Examining the Evidence and Links

December 13, 2025 •

3 min read

While it is a common concern, no direct evidence confirms that B12 deficiency causes cancer. However, research shows a complex relationship, with low vitamin B12 levels sometimes indicating underlying malignancies or increasing risk factors for certain cancers.

Quick Summary

This article explores the complex relationship between low vitamin B12 levels and cancer risk, explaining the difference between correlation and causation based on scientific studies.

Key Points

No Direct Causation: There is no direct evidence that B12 deficiency causes cancer; instead, low levels can be a sign of underlying disease.
Pernicious Anemia Link: A vitamin B12 deficiency caused by pernicious anemia significantly increases the risk of developing stomach cancer due to chronic inflammation.
Cancer Can Cause Deficiency: Certain malignancies, particularly those affecting the digestive tract, can interfere with the body's ability to absorb B12, leading to deficiency.
DNA Repair Impairment: Low B12 levels can impair DNA synthesis and repair, a mechanism that could potentially increase susceptibility to cellular mutations that lead to cancer.
Biomarker, Not Cause: In some cancer cases, high circulating B12 levels have been observed, possibly acting as a biomarker due to cancer cells producing B12-binding proteins.
Conflicting Supplement Research: Studies on B12 supplementation and cancer risk have yielded mixed results, with some linking high doses to increased risk (especially in male smokers) while others find no significant effect.
Medical Evaluation is Key: Unexplained or persistent B12 deficiency should prompt a thorough medical evaluation to rule out serious underlying conditions, including potential malignancies.

Understanding the Complex Link Between B12 and Cancer

Vitamin B12 is a vital nutrient involved in critical bodily functions like DNA synthesis and red blood cell formation. A deficiency can lead to health issues. The idea that B12 deficiency directly causes cancer is not supported by current scientific evidence. Instead, the relationship is more complex, with low B12 levels sometimes serving as an indicator of an underlying health problem or a risk factor in specific situations.

The Causal vs. Correlational Relationship

It's important to understand the difference between causation and correlation. While studies show correlations between B12 deficiency and cancer, this doesn't mean the deficiency causes the cancer. In fact, certain cancers, particularly in the gastrointestinal tract, can interfere with B12 absorption, leading to a deficiency as a result of the cancer.

B12's Role in DNA and Potential Risk

Vitamin B12 plays a role in DNA synthesis and repair. Low B12 can impair this process, potentially leading to genomic instability and increased susceptibility to mutations that could contribute to cancer development. This is a potential indirect link, not a direct cause.

Pernicious Anemia and Stomach Cancer Risk

Pernicious anemia, an autoimmune condition causing B12 malabsorption, is a well-established risk factor for stomach cancer. The chronic stomach inflammation associated with pernicious anemia increases this risk. Health organizations recognize this specific association. In this case, B12 deficiency is linked to a condition that raises cancer risk.

How Cancer Can Cause B12 Deficiency

Cancer can also lead to B12 deficiency:

Gastrointestinal Cancers: Tumors in the stomach or small intestine can impede B12 absorption.
Blood Cancers: Certain blood cancers can affect red blood cell production, sometimes mimicking or causing B12 deficiency symptoms.
Cancer Treatments: Therapies like chemotherapy and radiation can damage the digestive system, impairing nutrient absorption, including B12.

The Role of High B12 Levels

Studies have also noted high plasma B12 levels in some cancer patients, often considered a biomarker for the cancer itself rather than a cause. This may be because some cancer cells overproduce B12-binding proteins.

Observational Studies and Conflicting Findings

Research on the link between B12 intake and cancer risk has produced inconsistent results. Some studies have suggested a link between high-dose B12 supplements and increased lung cancer risk in specific groups like smokers, while others found no effect on overall cancer incidence. Interpreting these studies requires caution, considering factors like lifestyle and genetics.

B12 Deficiency vs. Cancer Association


Factor	B12 Deficiency	Cancer	Causal Link	Notes
Pernicious Anemia	Direct cause via autoimmune attack.	Increased risk of stomach cancer.	Yes (Indirect): Deficiency-driven condition increases cancer risk.	Screening for stomach cancer is often recommended.
Gastrointestinal Tumors	Can be a consequence of the disease.	Cause of the deficiency.	Yes (Reverse Causality): Cancer causes the deficiency.	Unexplained B12 deficiency may warrant investigation.
DNA Synthesis	Disrupts DNA repair, leading to instability.	Caused by cellular mutations and instability.	Potential (Indirect): Impaired DNA repair is a risk factor.	Folate and other B vitamins are also involved.
High Plasma B12	Not applicable; B12 levels are high.	Can be correlated, possibly as a biomarker.	No (Biomarker): Elevated levels are a symptom.	Certain cancer cells may overproduce B12-binding proteins.

Conclusion

In conclusion, B12 deficiency does not directly cause cancer. The relationship is intricate, with deficiency potentially indicating an underlying health issue, including malignancy. Pernicious anemia, a cause of B12 deficiency, is a known risk factor for stomach cancer. Impaired DNA synthesis due to low B12 could also increase cancer susceptibility. Understanding this complex association is vital for diagnosis and management. Persistent or unexplained B12 deficiency symptoms should be evaluated by a healthcare professional to rule out serious conditions.

An authoritative source on general cancer information is the National Cancer Institute.

Frequently Asked Questions

No, a vitamin B12 deficiency does not automatically mean you have cancer. It has numerous non-cancerous causes, but it can sometimes be a sign that warrants further medical investigation.

Research on high-dose B12 supplements and cancer risk has produced mixed results. Some studies suggest a link, particularly in male smokers taking very high doses, but it is not considered a direct cause.

Pernicious anemia, an autoimmune disease affecting B12 absorption, can cause chronic stomach inflammation. This inflammation increases the long-term risk of developing stomach cancer.

While not causing them directly, B12 deficiency is most consistently linked to an increased risk of gastric (stomach) and colorectal cancers, especially with pernicious anemia. Other links are less consistent.

Yes, treatments like chemotherapy and radiation can damage the digestive tract, leading to malabsorption and potentially causing or worsening a B12 deficiency.

Diagnosis typically involves a blood test to measure vitamin B12 levels. Additional tests may be used to confirm the deficiency and identify its cause.

Having B12 deficiency alone isn't a reason to assume cancer. However, if it's unexplained or with other concerning symptoms, consult a healthcare provider for evaluation to determine the root cause.