What it does in the body
Vitamin B12's primary functions are in the formation of red blood cells and the maintenance of a healthy nervous system. B12 is necessary for the synthesis of DNA during cell division. This is especially important in tissues where cells are dividing rapidly, particularly the bone marrow tissues responsible for red blood cell formation. If B12 deficiency occurs, DNA production is disrupted and abnormal cells called megaloblasts occur, which results in anemia. Symptoms include excessive tiredness, breathlessness, listlessness, pallor and poor resistance to infection. Other symptoms can include a smooth, sore tongue and menstrual disorders.¹

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. Prolonged B12 deficiency can lead to nerve degeneration and irreversible neurological damage.²

When deficiency occurs, it is often linked to a person's inability to effectively absorb B12 from the intestine rather than to a dietary deficiency. The subsequent anemia that may result is treated with injections of B12.³

Food Sources

• Animal products such as meat, eggs and dairy are a primary source of B12.  Additionally, B12 is increasingly used to fortify foods such as soy milk and breakfast cereals.⁴

Recommended Dietary Allowance

• The RDA for vitamin B12 ranges from 1.8 to 2.8 micrograms.⁵    There is no known toxicity.

Orthomolecular Dosage Range:

•  Much higher than RDA levels.  500-1,000 mcg.

"Many psychotic patients may require B12: as many as half of all patients admitted to mental hospitals may be deficient, even when no pernicious anemia is present. It is recommended for chronically depressed, neurasthenic, or psychotic patients; those with periodic psychosis or atypical manic-depressive psychosis; or manic-depressives with a family history of cancer, premature graying, autoimmune disease, and psychiatric disturbances (especially senile dementia or recurrent depressions)-all should have serum B12 testing done.⁶ Researchers have found that some psychiatric patients diagnosed organic psychosis, endogenous depression, or schizophrenic and neurotic depression were low in B12 and also low in folate. Few had pernicious anemia."⁷    (From: Hoffer A and Saul AW. Orthomolecular Medicine for Everyone, Basic Health Publications, 2008.)

References:

¹    Vitamin A (Retinol). Site viewed December 9, 2007.  http://www.vivo.colostate.edu/hbooks/pathphys/misc_topics/vitamina.html
²    Ibid.
³    Ibid.
⁴    Ibid.
⁵    Canadian Health Network. Public Health Agency.
⁶    Reading, C.M. "Latent Pernicious Anemia: A Preliminary Report." Med J Aust 1 (1975): 91-94.
⁷    Carney, M.W.P. "Serum Vitamin B12 Values in 374 Psychiatric Patients." Behav Neuropsych 1 (1969): 19-22.