kobalamina

Kobalamina, commonly known as cobalamin or vitamin B12, refers to a group of cobalt-containing compounds that function as essential nutrients in humans. It exists in several forms, including methylcobalamin and adenosylcobalamin, which act as enzymatic cofactors, and cyanocobalamin, a common synthetic form used in supplements and fortification.

Kobalamina is synthesized only by certain bacteria and archaea; humans obtain it from animal-derived foods or fortified products. In foods, B12 is typically bound to proteins and becomes available after release by stomach acid and pancreatic enzymes. Absorption requires intrinsic factor, a protein produced by gastric parietal cells; the B12-intrinsic factor complex is absorbed in the terminal ileum and transported in the blood mainly bound to transcobalamin II.

Biological roles of kobalamina include its function as a coenzyme for methionine synthase, which is involved in DNA synthesis and methylation, and for methylmalonyl-CoA mutase, important in fatty acid metabolism. Adequate B12 is necessary for nerve function and the maintenance of myelin.

Deficiency can lead to megaloblastic anemia and neurological symptoms, including neuropathy and cognitive changes. Serum measurements of methylmalonic acid and homocysteine can aid in diagnosis. Common risk factors include vegan or strict vegetarian diets, pernicious anemia, certain gastrointestinal disorders, and aging.

Dietary sources include meat, fish, dairy, and eggs; fortified cereals and supplements provide options for those avoiding animal products. Recommended daily allowances vary by age and life stage, typically around 2.4 micrograms for adults. High-dose supplementation is generally safe and used to treat deficiency or for at-risk groups.