[<< wikibooks] Structural Biochemistry/Chemistry of important organic molecules in Biochemistry/Vitamin B12
== Introduction ==
Vitamin B12, also known as cobalamin, is a vitamin that is water soluble and has a key role in ensuring that the brain and the nervous system functions normally. It is also essential for the formation of blood. It is usually involved in the metabolism or all cells within the human body and it affects DNA synthesis and regulation. Vitamin B12 is noted as the largest and most structurally complicated vitamin. It is typically produced industrially through bacterial fermentation-synthesis. 

== Medical Usage ==
Vitamin B12 is utilized to treat hereditary deficiency of transcobalamin II, cyanide poisoning, and vitamin B12 deficiency. It is also provided to detect pernicious anemia through the Schilling test. A sufficient amount of vitamin B12 levels can effectively protect elders from brain atrophy or shrinkage, which is linked to Alzheimer’s disease and impairment in cognitive function. 
Typically, the recommended intake for vitamin B12 is approximately 2 to 3 micrograms per day. It is usually taken orally in amounts that do not exceed the recommended dietary allowance. 

== Adverse Effects ==
Even after an intake of enormous amounts, vitamin B12 does not necessarily appear harmful to individuals who are healthy due to its low toxicity.
Treatment of vitamin B12 deficiency can result in the unmasking of polycythemia vera, which can be described as an increase in blood volume and red blood cells. Using vitamin B12 to correct megaloblastic anemia can cause fatal gout and hypokalemia.
Vitamin B12 is contraindicated in early Leber’s disease. Leber’s disease is a hereditary optic nerve atrophy.

== References ==
Lonn E, Yusuf S, Arnold MJ, et al. (2006). "Homocysteine lowering with folic acid and B vitamins in vascular disease".The New England Journal of Medicine 354
Yamada K, et al. (2008) "Degradation of vitamin B12 in dietary supplements." Int J Vitam Nutr Res. 78 (4-5): 195-203.