Vitamin B12 (cobalamin).
Vitamin B12 deficiency is often observed in alcoholics. Loss of myelin is also observed in patients with vitamin B12 deficiency. Cobalamin is involved in the myelination of axons and is a cofactor of methylmalonyl-CoA mutase, an enzyme involved in the oxidation of odd-carbon fatty acids. As a result, vitamin B12 deficiency affects the metabolic processes leading to the corresponding disorders.