B12 vs folate — what's the difference?
Both are B vitamins essential for red cell formation and methylation. B12 deficiency causes neurologic damage; folate deficiency does not. Treating folate alone can mask B12 deficiency.
Full answer
Vitamin B12 and folate (B9) are both essential for DNA synthesis, methylation, and red blood cell formation, and deficiency of either produces a macrocytic anemia. The clinical separation matters: B12 deficiency uniquely causes irreversible neurologic damage (peripheral neuropathy, posterior column dysfunction, cognitive decline), while folate deficiency does not. Treating folate alone in someone who is actually B12 deficient can correct the anemia while neurologic damage continues to progress. For this reason, B12 and folate are assessed together, and methylmalonic acid is used to confirm functional B12 deficiency when serum B12 is borderline.
Educational. Not a substitute for individualized provider review.
- B12 — Primary source · oMeds
- Reviewed by Dr. Laura Purdy, MD, MBA · Clinical Director, oMeds · Last reviewed 2026-05-29