Vogiatzoglou A, Smith AD, Nurk E, Berstad P, Drevon CA, Ueland PM, et al. Dietary sources of vitamin B-12 and their association with plasma vitamin B-12 concentrations in the general population: the Hordaland Homocysteine Study. Am J Clin Nutr 2009;89:1078-87. [ PubMed abstract] Pan Y, Liu Y, Guo H, Jabir MS, Liu X, Cui W, et al. Associations between folate and vitamin B12 levels and inflammatory bowel disease: A meta-analysis. Nutrients 2017;9:382. [ PubMed abstract]

It is primarily found in animal-based foods, including beef, salmon, yogurt, and milk, though some plant-based foods, like nutritional yeast, are fortified with it. If your body has difficulty absorbing vitamin B12, your doctor may recommend intramuscular injections of B12 to increase your levels. swelling (inflammation) in your intestines because of conditions like Crohn’s disease and coeliac diseaseVitamin B12 is a water-soluble vitamin that is naturally found in animal products. Some fortified foods, dietary supplements, and medications contain a synthetic version of vitamin B12. When you eat meat, fish, eggs, or dairy products, vitamin B12 is released from protein by hydrochloric acid and enzymes in the stomach; synthetic vitamin B12 is already in this released (free) form. Free vitamin B12 then combines with intrinsic factor — a substance secreted by the stomach cells—which enables it to be absorbed from the small intestine. Who needs more B12? A comparative animal study on the effectiveness of methylcobalamin and cyanocobalamin supplementation has reported that urinary excretion of cyanocobalamin was 3 times higher than that of methylcobalamin. Rizzo G, Lagana AS. (2020) A review of vitamin B12. In Patel VB. (Ed.) Molecular Nutrition: Vitamins 105-129 Academic Press.

Rojas Hernandez CM, Oo TH. Advances in mechanisms, diagnosis, and treatment of pernicious anemia. Discov Med 2015;19:159-68. [ PubMed abstract] Therefore, vitamin B12 deficiency may lead to decreased serotonin production, which can cause a depressed mood. This is a fact sheet intended for health professionals. For a general overview of Vitamin B12, see our consumer fact sheet on Vitamin B12. IntroductionKim S, Choi BY, Nam JH, Kim MK, Oh DH, Yang YJ. Cognitive impairment is associated with elevated serum homocysteine levels among older adults. Eur J Nutr 2019;58:399-408. [ PubMed abstract] Oliai Araghi S, Kiefte-de Jong JC, van Dijk SC, Swart KMA, Ploegmakers KJ, Zillikens MC, et al. Long-term effects of folic acid and vitamin-B12 supplementation on fracture risk and cardiovascular disease: Extended follow-up of the B-PROOF trial. Clin Nutr 2021;40:1199-1206. [ PubMed abstract] Recommended Dietary Allowance (RDA): Average daily level of intake sufficient to meet the nutrient requirements of nearly all (97%–98%) healthy individuals; often used to plan nutritionally adequate diets for individuals