Vitamin B12 (cobalamin) is an essential nutrient of critical importance for general health. It plays a crucial role in the body's metabolic functions, DNA synthesis, and the sustainability of the hematopoietic system. It is also necessary for myelin sheath synthesis (myelination) in the central nervous system. Vitamin B12 deficiency is generally defined by a drop in serum or plasma B12 levels below 148 pmol/L (200 pg/mL).