Vitamin B12 (cobalamin) is an essential nutrient that supports nerve function, red blood cell formation, and DNA synthesis. Most people associate B12 with deficiency, which causes anemia and neurological problems. However, a growing body of research has found that elevated B12 levels in the blood are associated with an increased risk of certain cancers, including lung and colorectal cancer.
The body stores most of its B12 in the liver. When the liver is damaged or when liver cancer is present, stored B12 leaks into the bloodstream, raising circulating B12 levels. Colorectal cancer frequently spreads to the liver, which is the most common site of distant metastasis in colon cancer. Researchers therefore hypothesized that elevated B12 at the time of colon cancer diagnosis might reflect liver involvement by cancer and could serve as a prognostic warning sign.
This study used a massive global clinical database to examine whether B12 levels at the time of colon cancer diagnosis were associated with survival and metastatic spread. It also explored the biology of B12 metabolism in colon tumors using gene expression data, seeking to understand the mechanism behind any clinical association.
Researchers used TriNetX, a global federated health research network that aggregates de-identified electronic medical records from 108 healthcare organizations worldwide. From over 550,000 patients with a colon cancer diagnosis (ICD-10 code C18), they identified 37,106 patients who had at least one vitamin B12 measurement taken within one year of their initial diagnosis.
Patients were divided into three groups based on their B12 levels: elevated (greater than 1,000 pg/mL), normal (300 to 1,000 pg/mL), and low (less than 300 pg/mL). To ensure fair comparisons, propensity score matching (PSM) was used to create matched patient groups balanced for demographics, prior metastatic disease, cancer treatments, and B12-related conditions such as pernicious anemia or prior stomach surgery.
Survival was measured as time from diagnosis to death. One-year incidence of new metastases (to liver, lung, and peritoneum) and abnormal liver enzyme levels were compared between groups. A separate gene expression analysis using The Cancer Genome Atlas (TCGA) and the GTEx database examined whether genes involved in B12 metabolism were differently expressed in colon tumors compared to normal colon tissue, and whether their expression affected survival.
The survival differences between B12 groups were striking. Patients with elevated B12 had a median overall survival of just 59.4 months, compared to 129.8 months for normal B12 patients and 137.3 months for low B12 patients. After propensity score matching, elevated B12 remained independently associated with significantly worse survival, with a hazard ratio of 1.65 compared to normal B12 patients (meaning 65 percent higher risk of death at any given time point).
Critically, this survival disadvantage held up after accounting for known confounders in multivariable analysis. Among factors that independently predicted worse survival were older age, male sex, Black race, prior metastatic disease, and prior use of fluorouracil (a commonly used colon cancer chemotherapy). Factors associated with better survival included adequate folate levels and having undergone colonoscopy with polyp removal.
Interestingly, low B12 patients had survival outcomes similar to normal B12 patients, not worse. This suggests that B12 deficiency itself does not worsen colon cancer outcomes, and that the prognostic signal is specifically tied to elevated, not merely abnormal, B12. This pattern supports the hypothesis that high B12 is reflecting underlying cancer biology rather than nutritional status.
Among patients with staging data available, those with elevated B12 were more likely to have stage 4 (advanced) disease at diagnosis: 54 percent of high B12 patients had stage 4 cancer, compared to 36 percent of normal B12 patients. High B12 patients were also more likely to have T4 tumors (where the cancer has grown through the bowel wall) and to have detectable metastases at the time of diagnosis.
Looking at metastatic events within one year after diagnosis, high B12 patients had significantly higher rates of new spread to all sites (41.7% vs. 32.1%), liver (23.1% vs. 14.8%), lung (9.6% vs. 6.7%), and peritoneum (10.5% vs. 7.6%) compared to matched normal B12 patients. The risk ratios for liver and all-site metastases were especially high, pointing to a strong link between elevated B12 and liver involvement.
High B12 patients were also significantly more likely to show elevated liver enzymes within one year of diagnosis, including elevated alkaline phosphatase (57.4% vs. 40.8%), AST, ALT, and bilirubin. Elevated liver enzymes are a sign of liver stress or damage, consistent with liver metastases displacing normal liver tissue and releasing stored B12 into the blood.
To probe the biological mechanism connecting B12 to colon cancer outcomes, researchers analyzed the expression of 11 genes involved in B12 and folate metabolism in colon cancer tissue compared to normal colon tissue. They used publicly available data from 283 colon cancer tumor samples and 304 normal colon tissue samples.
The most important finding was that methionine synthase (MTR), a key enzyme that uses B12 as a cofactor to convert the amino acid homocysteine into methionine, was significantly overexpressed in colon cancer tumor tissue compared to both normal adjacent colon tissue and normal tissue from healthy individuals. This suggests that colon tumors are metabolically dependent on B12-driven methionine synthesis, possibly as a fuel for rapid cell division.
Patients with higher MTR gene expression in their tumors had a median overall survival of 65.8 months, while those with low MTR expression had a median survival that was not yet reached at the time of analysis (meaning most low-MTR patients were still alive). The hazard ratio for high MTR expression was 1.74 (74 percent higher risk of death). This gene-level finding provides a biological explanation for why elevated serum B12 might predict worse outcomes: cancers that aggressively consume B12 via MTR may release more B12 into circulation and may be more metabolically aggressive.
These findings suggest that measuring vitamin B12 at the time of colon cancer diagnosis could provide clinically useful prognostic information. A serum B12 level above 1,000 pg/mL appears to be a warning sign for more aggressive disease with higher metastatic potential, particularly to the liver, and worse overall survival. This is a simple, inexpensive blood test that is already routinely available in most clinical settings.
Importantly, these results do not suggest that patients should take steps to lower their B12 levels. High B12 appears to be a consequence of aggressive cancer biology, not a cause of it. The elevated B12 likely reflects ongoing liver involvement by metastatic cancer cells rather than representing an independent driver of tumor growth. Patients should not stop taking prescribed B12 supplements without discussing it with their doctor.
Looking ahead, the MTR gene finding opens a possible therapeutic angle: if colon cancer cells depend heavily on B12-mediated one-carbon metabolism for growth, drugs that target MTR or the broader methionine synthesis pathway might be developed as treatments. Future studies should prospectively validate B12 as a prognostic biomarker, explore how it interacts with specific treatment regimens, and examine whether MTR inhibition could slow tumor growth or metastasis.