Table 2.

Stages of cobalamin metabolism and corresponding causes of cobalamin deficiency [13, 15].

Stages and factors involved in cobalamin metabolism	Causes of cobalamin deficiency
Ingestion of food	Strict vegetarianism (patients who are sick in institutions or in psychiatric hospitals)
Digestion, which involves haptocorrin, gastric secretions (HCl and pepsin), intrinsic factor, pancreatic and biliary secretions, and the enterohepatic cycle	Gastrectomy, pernicious anemia, and food-cobalamin malabsorption
Absorption, which brings into play intrinsic factor and cubilin	Ileal resection, malabsorption, pernicious anemia, and food-cobalamin malabsorption
Transportation by transcobalamins	Congenital deficiency in transcobalamin II
Intracellular metabolism by various intracellular enzymes	Congenital deficiency in various intracellular enzymes

HCl = hydrochloric acid.