Vitamins are often presented as simple solutions for improving health. The common belief is that getting enough of them helps the body function properly, while deficiencies create problems. However, vitamin B12 shows that the relationship between nutrients and health can be far more complex.
For decades, vitamin B12 has been considered essential for energy, brain function and overall wellbeing. It is often recommended for people experiencing fatigue, cognitive issues or those following plant-based diets. But recent research has raised questions about the relationship between B12 levels and cancer.
Why vitamin B12 is important for the body
Vitamin B12, also known as cobalamin, is a nutrient that the body cannot function without. It plays a key role in:
- DNA production and repair.
- Maintaining the myelin sheath that protects nerves.
- Producing mature red blood cells.
- Supporting fat and amino acid metabolism.
The vitamin is naturally found mainly in animal-based foods, which is why people following strict plant-based diets or those with absorption problems can develop deficiencies.
The surprising connection between B12 and cancer
Because vitamin B12 is involved in DNA creation and repair, researchers initially explored whether insufficient levels could contribute to cancer development. The theory was that low B12 could impair DNA repair processes, increasing mutations and potentially promoting tumor growth.
However, some studies found the opposite pattern. Researchers observed unusually high blood levels of B12 among people diagnosed with cancers including lung, breast, esophageal and colorectal cancer.
This created a more complicated question: does high B12 contribute to cancer, or is it a result of the disease?
High B12 levels may be a symptom, not a cause
Scientists emphasize that blood levels of vitamin B12 are not the same as the amount someone consumes through their diet. Blood concentrations are influenced by how the body stores, transports and processes the vitamin.
Cancer can disrupt these processes. Tumors, particularly aggressive cancers or cancers affecting the liver, may interfere with how B12 is stored and released. Some tumors may also increase production of proteins responsible for transporting B12 through the bloodstream.
As a result, elevated B12 levels could be a biological signal of disease activity rather than evidence that excess vitamin intake causes cancer.
Research on vitamin B12 and colorectal cancer outcomes
A study published in Cancer Research Communications analyzed health records from 37,106 colorectal cancer patients across 108 healthcare systems.
The researchers found that patients with elevated B12 levels above 1,000 picograms per liter had significantly different outcomes compared with those with normal levels.
- Patients with high B12 had a median survival of around five years.
- Patients with normal B12 levels survived nearly 11 years on average.
- High B12 levels were associated with roughly twice the risk of death compared with low levels.
- Patients with elevated B12 were more likely to have advanced-stage cancer and develop new metastases.
The study also examined tumor samples and found increased activity in the MTR gene, which produces an enzyme that requires B12 to support DNA-related processes. Tumors with higher MTR activity were associated with poorer survival outcomes.
The findings suggest that aggressive tumors may be more capable of using and accumulating B12 to support rapid growth.
Both low and high B12 levels remain under investigation
While elevated B12 has been linked with poorer outcomes in some cancer studies, low levels remain an area of uncertainty.
A 2024 study involving thousands of cancer patients and individuals without cancer found a U-shaped relationship between dietary B12 intake and cancer risk. Both unusually low and unusually high intake levels were associated with increased risk compared with moderate intake.
However, the study was observational and relied on food questionnaires, meaning it could identify associations but could not prove that B12 levels directly caused cancer.
Researchers also noted that the highest intake group consumed around 2.97 micrograms of B12 per day, only slightly above standard nutritional recommendations of approximately 2.4 to 2.8 micrograms daily.
The current scientific view on B12 and cancer
The relationship between vitamin B12 and cancer remains unresolved. Current evidence does not show that taking B12 supplements causes cancer, nor does it prove that B12 protects against the disease.
Instead, researchers increasingly believe that abnormal B12 levels may reflect underlying changes in the body caused by cancer or other health conditions.
Vitamin B12 remains an essential nutrient, but the latest research suggests that its role in cancer is more complicated than simply having too little or too much.
