Vitamin B12 in Vegetarian Diets

Vitamin B12 (B12) belongs to a group of water soluble B-vitamins. Methylcobalamin and adenosylcobalamin are two biologically active forms of B12. Hydroxocobalamin, aquacobalamin, nitrocobalamin and cyanocobalamin are metabolized to either of the two active forms once ingested. B12 is essential in synthesis of methionine (methylcobalamin) and in metabolism of lipids, protein and carbohydrates (adenosylcobalamin). Deficiency of B12 is widespread. Vegetarians develop B12 deficiency because of inadequate intake. The deficiency is prevalent regardless of other factors such as demographic characteristics , place of residency, or age. Vegans are at an especially high risk. Deficiency leads to hyperhomocys-teinemia. High prevalence of hyperhomocysteinemia has been reported among individuals who adhere to all types of vegetarian diets. Symptoms of B12 deficiency may be mild (e.g. fatigue, difficulty to concentrate) or severe (low bone mineral density (BMD), hearing loss, brain atrophy, and/or hardening of arteries). Intake of eggs, milk and dairy products does not guarantee adequate B12 status. In fact, B12 intake from these products is likely inadequate to maintain sufficient serum B12 concentration. Although fortified foods may help to delay the onset of deficiency, low B12 concentrations and B12 deficiency have been reported in studies with vegetarians who used fortified foods and those who used supplements (perhaps indicating inadequate dose of a supplement). Individuals who adhere to all types of vegetarian diets should be advised to routinely screen for B12 status. The best assessment method of B12 is methyl-malonic acid and/or holotranscobalamin II. Vegetarians need to ensure they ingest a reliable B12 source (e.g. B12 supplements). The dose depends large on age and life stage with elderly and pregnant vegan women having the need for the highest supplemental dose. Vitamin B12 (B12), named cobalamin, belongs to a group of water soluble B-vitamins. Methylcobalamin and ad-enosylcobalamin are two biologically active forms of B12. Hydroxocobalamin, aquacobalamin, nitrocobalamin and cyanocobalamin are metabolized to either of the two active forms once ingested (1). Methylcobalamin is a co-factor in the conversion of homocysteine to methionine. Adenosylcobalamin is needed for the conversion of Meth-ylmalonyl-CoA to succinyl-CoA. This form is involved in the metabolism of fats, carbohydrates and protein. B12 is essential in DNA synthesis, and thus, in synthesis of all new cells. B12 plays a critical role in erythropoiesis and it is indispensable in synthesis and maintenance of myelin, a coating of the nerve pathways (1). The process of digestion and absorption of B12 requires adequate synthesis of hydrochloric acid, …