Vitamin B-12 is a micronutrient. It can be one of three different related chemical compounds. It is used by practically every cell in the body, but has great importance in the formation of red blood cells and regulating nerve function. Vitamin B-12 deficiency can lead to anemia and neurological symptoms such as ataxia.
Vitamin B-12 is synthesized in nature by bacteria, and is found in meat, particularly organ meat. It is regularly disposed of by the body, but Vitamin B-12 in the liver can be stored there for over a year (which is why organ meats such as liver are so rich in the vitamin).
Pernicious anemia is a form of Vitamin B-12 deficiency caused by the failure of the body to extract the vitamin from the diet, which is done by enzymes in the small intestine. However, vitamin B-12 can be injected intravenously in such cases.