kobalamiin

Kobalamin, commonly known as vitamin B12 in humans, is a family of corrin-based compounds that contain a cobalt ion at its center. It is essential for DNA synthesis, red blood cell formation, and neurological function. The term kobalamin encompasses four biologically active forms: methylcobalamin and adenosylcobalamin function as endogenous coenzymes, while cyanocobalamin and hydroxocobalamin are commonly used in supplements or as pharmaceutical preparations.

Dietary sources are animal-origin foods; vegetarians may rely on fortified foods or supplements. Absorption occurs in the small intestine and requires intrinsic factor produced by gastric parietal cells. After absorption, transcobalamin II transports B12 in plasma with hepatic storage in the liver, capable of lasting years.

B12 acts as a cofactor for methionine synthase, catalyzing remethylation of homocysteine to methionine, and for methylmalonyl-CoA mutase, converting methylmalonyl-CoA to succinyl-CoA, a step in odd-chain fatty acid and amino acid metabolism. Deficiency can cause megaloblastic anemia and progressive neuropathy; pernicious anemia is a common cause due to lack of intrinsic factor. At-risk groups include older adults, people with pernicious anemia, those with gastric bypass surgery, and vegans without fortified foods.

Diagnosis relies on measurements of serum B12, methylmalonic acid, and homocysteine; treatment includes oral or parenteral B12, often starting with injections for rapid correction. Excess intake generally has low toxicity, with minimal adverse effects.