Too little vitamin B12 can damage genetic material and increase cancer risk, though some studies implicate high levels of the crucial vitamin with certain cancers and poorer outcomes in cancer patients.

A 2025 study from Vietnam found increased cancer risk for both low and excessively high B12 consumption, indicating that balance matters. An earlier Chinese study showed that supplements of combined B-vitamins decreased risk of developing skin melanomas. However, another study found that vitamin B6 and B12 supplements in particular correlated with a 30% to 40% increase in lung cancer risk among men, with worse outcomes for those taking higher doses and for smokers.

Vitamin B12, or cobalamin, is a water-soluble vitamin necessary to the development of nerve cells, healthy red blood cell formation and DNA synthesis, according to the National Institutes of Health. Bound to protein in foods, B12 must be released before the body can use it, and some people have difficulty processing the compound. B12 deficiency has been linked to fatigue, neurological changes, anemia, inflamed tongue and low blood cell counts.

The vitamin is essential to healthy cell reproduction, research shows, but more is not better. B12 supports cell growth, but those benefits also may help unhealthy, or precancerous cells thrive, though this remains unproved in human studies.

While B12 is prevalent in the blood of some cancer patients, researchers remain divided as to whether it causes or aids cancer growth, or if cancer somehow causes B12 levels to increase. The connection is strong enough that elevated B12 levels in the blood may be used by doctors to justify cancer screening.

A large-scale 2026 study in Cancer Research Communications found that colon cancer patients with very high B12 levels survived on average around five years, compared with nearly 11 years for patients showing more normal levels.

And a February study in Molecular Cell found that Vitamin B7, or Biotin, gave some tumors an alternate means to produce the necessary energy to divide and grow.

©2026 The Baltimore Sun. Visit at baltimoresun.com. Distributed by Tribune Content Agency, LLC.