Prototype of the family of naturally occurring cobalt coordination compounds knows as corrinoids. Analogs of vitamin B12 which differ only in the β-ligand of the cobalt are termed cobalamins. Synthesized almost exclusively by bacteria. Dietary sources include fish, meat, liver, and dairy products; plants have little or no cobalamins. Converted by the body into its bioactive forms, methylcobalamin and cobamamide, which serve as enzyme cofactors. Severe deficiency may result in megaloblastic anemia and/or neurological impairment.