Nutrition & DietVitamin B12 and Cancer Risk — Why More Is Not Always Better
Vitamin B12 is essential for DNA repair, red blood cell production, and nerve health — but emerging research is complicating the simple 'more is better' narrative. A 2025 Vietnamese case-control study found a U-shaped relationship between B12 intake and cancer risk, meaning both deficiency and excess were linked to higher risk. High-dose B12 supplements have not been shown to protect against cancer overall, and some studies suggest a slight increase in lung cancer risk among long-term, high-dose users — particularly men and smokers. Researchers also note that elevated B12 in cancer patients may reflect the disease itself rather than a cause. For most healthy adults, balance through diet remains the safest approach.
