Abstract
Vitamin B12 (B12) is essential in activating folate needed in DNA synthesis. Inadequate intake results in the impairment of nerve transmission and inadequate synthesis of erythrocytes and other hematological cells. Two separate mechanisms of B12 absorption exist, a receptor-mediated endocytosis that occurs in the distal ileum and the mass-action pharmacologic mechanism. The recommended dietary allowance for B12 for adults issued by the Institute of Medicine is 2.4 μg/d. B12 is only found in meats and other foods of animal origin. B12 deficiency is widespread. Two main causes of deficiency include inadequate absorption and intake. Elderly and vegetarians are at highest risk for deficiency. Prevalence of deficiency ranges from 7% of the US population 3 years and older to 90% among vegans. The best way to assess deficiency is by using methylmalonic acid. Populations at risk could benefit from using B12 supplements and from fortification of flour. © 2013 The Author(s).