Although vitamins are often viewed as simple and beneficial dietary elements, the relationship between nutrients and health can be more intricate, with vitamin B12 being a notable example. Also known as cobalamin, B12 is vital for various bodily functions, including DNA formation, maintenance of the protective myelin sheath of nerves, red blood cell maturation, and the metabolism of fats and amino acids.
This vitamin is found naturally only in animal products, making people on strictly vegetarian diets or those with absorption difficulties susceptible to B12 deficiency. For many years, it was seen as a nutritional ally to combat symptoms such as fatigue or difficulty concentrating.
However, recent scientific research has revealed a more complicated connection between B12 and cancer. Studies have identified both very low and high levels of B12 in the blood of individuals diagnosed with tumors in organs such as the lungs, breast, esophagus, and colon.
This raises the question of whether excess B12 can promote cancer or if the tumors themselves can cause the increase in vitamin in the blood. It is crucial to note that blood levels do not necessarily correspond to intake; they depend on how the body stores, uses, and transports the nutrient, a process that can be affected by cancer.
The liver acts as a large reservoir of B12. Tumors, especially hepatic ones or aggressive cancers, can alter how this reserve is managed. Furthermore, some tumors can increase the production of proteins responsible for transporting B12, meaning that a high blood test result may be a consequence of cancer, not the cause of the disease.
A study published this year in the journal Cancer Research Communications investigated 37,106 patients with colorectal cancer, using a global database with information from 108 healthcare systems. The results showed significant differences: patients with high B12 levels (above one thousand picograms per liter) had a median survival of about five years, while those with normal levels achieved nearly 11 years. Interestingly, patients with low levels showed slightly better performance.
Even after adjusting for variables such as age and treatment, patients with elevated B12 showed approximately double the risk of mortality compared to those with low levels, and a death risk 65% higher than those with normal levels. These patients with high B12 also had a greater chance of already having stage 4 cancer at diagnosis or developing new liver metastases within a year.
The analysis of hundreds of colon tumors revealed significantly higher activity of a gene called MTR, linked to the production of an enzyme that requires B12 to form a component of DNA. Tumors with this more active version of the gene were associated with the worst survival prognoses, suggesting that more aggressive tumors may use more B12 for rapid proliferation, rather than the excess of the vitamin causing the cancer.
Additional research, including a 2024 study on cancer immunotherapy and analyses in mouth cancer patients, confirmed this link between high B12 levels and less favorable outcomes. A 2024 evidence review emphasized that the significance of these elevated levels remains uncertain and may be related to reverse causality, meaning cancer may elevate B12, not the other way around.
However, the question persists as to why low B12 levels might increase the risk of cancer. A 2024 study followed 3,758 cancer patients and 2,995 without the disease in Vietnam, finding a U-shaped relationship: both very low and very high dietary B12 intake were linked to a higher risk of cancer compared to moderate intake. However, because it was observational and dependent on participant memory, this study only points to associations, not proof of causality.
Additionally, the highest consumption group registered an average of only 2.97 micrograms of B12 per day, a value close to the standard recommendations of 2.4 to 2.8 micrograms. Given this, the relationship between B12 and cancer is still unclear, but the evidence increasingly points to the vitamin levels serving as an indicator of organic processes, and not necessarily as a causative factor.