Methylcobalamin & Adenosylcobalamin: Understanding Vitamin B12 Forms

Vitamin B12 is a large, chemically complex nutrient. Several variants of vitamin B12 exist, including methylcobalamin, adenosylcobalamin, cyanocobalamin, aquacobalamin and hydroxocobalamin. The term cobalamin refers to any member of the B12 group; the name derives from presence of a cobalt atom in the molecular structure.

Cyanocobalamin

• The form of B12 most often sold in vitamin supplements is cyanocobalamin, which is a synthetic version of the vitamin. However, human metabolism cannot directly use cyanocobalamin. Instead, the compound must be converted to a usable form through the chemical processes of methylation or adenosylation.

Methylcobalamin

• Methylcobalamin results from breaking down other cobalamin compounds and attaching a methyl group. The methylated form of B12 is the main form of the vitamin found in human blood plasma and human breast milk.

Adenosylcobalamin

• Adenosylcobalamin results from breaking down other cobalamin compounds and attaching a chemical group containing adenosine, 5'-deoxyadenosinyl. Adenosylcobalamin is the primary form of B12 found in non-human animals. In humans, adenosylcobalamin is found mainly in tissues, especially the liver.