Why Vitamin B12 Deficiency Should be on your Radar Screen

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<strong>Vitamin</strong> <strong>B12</strong> <strong>Deficiency</strong> There are several important points about cobalamin absorption: It occurs primarily during the active digestion of animal proteins in the stomach and terminal ileum, and it depends on the availability of adequate amounts of a num<strong>be</strong>r of compounds, including the R protein (haptocorrin from saliva), gastric acid, pepsin, and intrinsic factor (IF).(2, 3) Gastric acid is needed to digest animal protein. When the ability to secrete that acid is lost, a person cannot break down the protein to release vitamin <strong>B12</strong> from food and can absorb only crystalline (synthetic) vitamin <strong>B12</strong>.(2) Loss of IF in pernicious anemia results in an inability to absorb vitamin <strong>B12</strong>. People with pernicious anemia must <strong>be</strong> treated with parenteral cyanocobalamin or high doses of oral cobalamin (1,000 micrograms [µg] daily).(2, 11) About 1% of large oral doses of vitamin <strong>B12</strong> passively diffuses into the bloodstream from the small intestine.(2, 10) If any aspect of the digestion sequence <strong>be</strong>gins to fail and malabsorption develops, the body can draw on the large amounts of vitamin <strong>B12</strong> stored in the liver, so overt symptoms might not develop for several years.(2, 10, 12) However, with certain conditions, vitamin <strong>B12</strong> deficiency might develop over a shorter period of time (months). Adequate serum levels of cobalamin are crucial to complete three enzymatic processes (Figure 1). Methylcobalamin is a cofactor necessary to convert homocysteine (Hcy) to methionine. Thus, vitamin <strong>B12</strong> deficiency increases Hcy.(1, 12, 13) The cofactor adenosylcobalamin is required for the conversion of methylmalonyl coenzyme A to succinyl coenzyme A.(2, 10) Methylcobalamin is needed to convert 5methyltetrahydrofolate to tetrahydrofolate and is necessary for DNA and red blood cell production. 15 Pernicious anemia is an autoimmune disease in which antibodies attack gastric cells, resulting in impaired production of intrinsic factor that is critical for absorption of vitamin <strong>B12</strong>.
<strong>Vitamin</strong> <strong>B12</strong> <strong>Deficiency</strong> Figure 1. The Biochemical Role of Cobalamin <strong>Vitamin</strong> <strong>B12</strong> deficiencies often, but not always, develop gradually over many years and are accompanied by a slow and varied onset of nonspecific symptoms. Carmel descri<strong>be</strong>s vitamin <strong>B12</strong> deficiency in two states: clinical and subclinical.(1) Clinical deficiency manifests with hematologic or neurologic signs and symptoms, cobalamin levels
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Why Vitamin B12 Deficiency Should be on your Radar Screen

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