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What role does cobalt play in vitamin B12?

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A color-coded periodic table of the elements displays each element's symbol and atomic number, with categories such as alkali metals, noble gases, halogens, transition metals, and actinoid elements distinguished by different background colors. — transition metal Modern version of the periodic table of the elements (printable).

Cobalt is a vital component of vitamin B12, serving as the central metallic ion within its complex chemical structure. It is the only known vitamin to contain such a heavy element, with cobalt accounting for approximately 4.3 percent of the vitamin's mass.123

In its biological role, vitamin B12 functions as a cofactor for enzymes involved in the metabolism of amino acids and fatty acids. It is essential for the maturation of red blood cells and the maintenance of neurological function, including the synthesis of fatty acids in the myelin sheath that protects nerve cells. Furthermore, it works in conjunction with folic acid to facilitate the synthesis of DNA, which is critical for cell division and growth. Because of these functions, cobalt—in the form of vitamin B12—is an essential trace element for human health and the nutrition of ruminants.13