Understanding Vitamin B₁₂

Abstract

Vitamin B 12 (B 12 ) 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 B 12 absorption exist, a receptor-mediated endocytosis that occurs in the distal ileum and the mass-action pharmacologic mechanism. The recommended dietary allowance for B 12 for adults issued by the Institute of Medicine is 2.4 µg/d. B 12 is only found in meats and other foods of animal origin. B 12 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 B 12 supplements and from fortification of flour.