Vegan and vegetarian diet: B12

Vitamin B12 is found only in animal products. Strict vegan and long-term vegetarian diets without supplementation lead to deficiency – in some people within 1–2 years, in others after 5–10 years due to hepatic stores. Deficiency causes macrocytic anaemia and irreversible neurological damage. Preventive B12 intake is routine for vegans and vegetarians. The dose and form are selected with a clinician based on serum B12 and homocysteine.

ICD-10 E53.81 drug

Also known as: B12 prevention in vegans, Plant-based diet and B12, Vegetarian B12 supplementation

Drugs used for this condition

AVitamin B12 (cobalamin)First line · Water-soluble B-vitamin; cofactor of methionine synthase and methylmalonyl-CoA mutaseVegan and long-term vegetarian diets without fortified foods are a major indication for preventive B12 intake. Without supplementation deficiency develops in some people within 1–2 years and in others over 5–10 years. NIH ODS 2024 and SEEN recommend 25–100 mcg of cyanocobalamin per day or 2000 mcg once weekly in vegans. Any iHerb form works; cyanocobalamin is cheaper and has the longest evidence base. Annual or biannual monitoring of B12, homocysteine and methylmalonic acid is appropriate. If you are vegan and not taking B12, discuss testing and a regimen with a clinician.

How to read tiers A–F

Evidence tiers belong to the drug-indication pair, not to the drug as a whole: the same substance can be A for one condition and F for another.

AStrong evidence – first or second line in international guidelines
BRecommended in selected cases
CStudy data contradict each other
DBenefit not proven, no documented harm
FDocumented harm, or risk without benefit