B12 is an essential vitamin that has no reliable known plant sources, and must therefore be obtained from fortified food products and/or supplements in a vegan diet

Vitamin B12 is required by the body in trace amounts. Deficiency is very serious and may cause irreversible nerve damage or death, as well as "pernicious" anaemia. While other B-complex vitamins are not stored in the body, B12 is, so deficiency symptoms may take months or years to appear. A tell-tale symptom is tingling in extremities like hands and feet, which should trigger an immediate visit to medical service to have blood B12 levels checked.

There are no reliable non-animal natural sources of B12 that have been shown to prevent deficiency, so vegans must obtain it from fortified foods and/or supplements. Absorption decreases with age, so people over 50 are advised to have their blood levels monitored and take supplements regardless of dietary choices.

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