Vitamin B12 deficiency is a frequent problem, especially in the elderly, caused by various causes, such as atrophic gastritis, gastrectomy or some medications. In this article we review aspects of the physiology and causes of this deficiency, as well as the evidences about its treatment. Several studies support the efficacy of high doses of vitamin orally, even in the absence of intrinsic factor (IF), for the treatment or prevention of B12 deficiency. This option, suitable for the majority of cases, also supposes a reduction of costs compared to conventional injectable therapy, avoids the inconveniences and risks that this implies and supposes a greater comfort for the patients.
Vitamin B12 or cobalamin plays a key role as a coenzyme in DNA synthesis and cell maturation. As well as in the synthesis of neuronal lipids. The human body is not able to synthesize it and must obtain it from the diet.
Vitamin B12 deficiency
Above all (Vitamin B12 deficiency) the vitamin ingested in the diet is separate from animal proteins by pepsin and gastric hydrochloric acid. Joining haptocorrin, a protein of salivary origin, which is dissociate in the duodenum by the action of pancreatic proteases. It is absorbe in the distal ileum, after passing through the small intestine linke to the intrinsic factor (FI). A protein synthesize in the parietal cells of the gastric fundus. The B12-FI complex binds to the ileal cell receptors and is absorbed by endocytosis. Vitamin B12 passes into the bloodstream bound to transcobalamin II.
Apart from this mechanism, between 1 and 2% of the B12 ingeste is absorbe by passive diffusion.
More than 75% of the cobalamin excreted by bile is reabsorbe. Its urinary elimination is usually low.
Certainly (Vitamin B12 deficiency) the daily requirements of vitamin B12 are approximately 2 to 2.5 μg, provided in a balanced diet3. The tissue stores of B12 are wide, between 3 and 10 mg, and can take decades to empty.
Vitamin B12 deficiency
Above all, the main causes of vitamin B12 deficiency is divide into three groups. Low exogenous intake, poor digestion and malabsorption of the vitamin. The first occurs in strict vegetarians and is rare. Therefore, before any patient with signs or symptoms of B12 deficiency, we must consider the possibility that there is a problem of digestion or absorption of base2.
The pathologies most frequently associated with poor digestion of B12 are atrophic gastritis, achlorhydria and gastrectomy. The causes of malabsorption is a classic example of megaloblastic anemia. Which the parietal cells are destroy by autoantibodies, producing an IF deficiency. That leads to insufficient absorption of cobalamin.