Vitamin B12 plays a vital role in the formation of red blood cells and in maintaining a healthy nervous system. B12 is necessary for bone marrow creation and aids digestion of carbohydrates, fats and proteins and contributes in synthesis of genetic material. It is especially necessary for the rapid synthesis of DNA during cell division. This is important in tissues where cells are dividing rapidly, particularly the bone marrow tissues responsible for red blood cell formation.

Vitamin B12 helps support healthy heart and cardiovascular functions. Homocysteine, a normal byproduct of protein metabolism, is a toxic amino acid that has been associated with increased risk of heart disease and stroke. In a healthy body, B12, B6, and folic acid help convert homocysteine into methionine, a beneficial amino acid. This process is called methylation. B12 and B6 together are also helpful for promoting vascular integrity.

B12 is also important in maintaining the nervous system. Nerves are surrounded by an insulating fatty sheath comprised of a complex protein called myelin. B12 plays a vital role in the metabolism of fatty acids essential for the maintenance of myelin.

B12 absorption by the body is crucial to avoid deficiencies. Absorption of B12 requires the secretion from the cells lining the stomach of a glycoprotein, known as intrinsic factor. The B12-intrinsic factor complex is then absorbed in the ileum (part of the small intestine) in the presence of calcium.

Vitamin B12 can be stored in small amounts by the human body; around 80% is stored in the liver. Adults can store up to 2-5mg of B12. Vitamin B12 is excreted in the bile and is effectively reabsorbed.This is known as enterohepatic circulation. The amount of B12 excreted in the bile can vary from 1 to 10ug (micrograms) a day.