Vitamin B12, also known as cyanocobalamin or cobalamin, is an essential water-soluble vitamin that plays a vital role in maintaining the normal functioning of the brain and nervous system, and erythropoesis (blood formation). Water-soluble vitamins dissolve in water. Trace amounts of vitamin B12 are found in the urine after being used by the body. Like the other eight B vitamins (vitamin B-complex), it aids in cellular metabolism, particularly in regulating and synthesizing DNA.  Vitamin B12 also takes part in energy production and fatty acid synthesis.

Aside from its functions in the body, it is also utilized for therapeutic purposes. Vitamin B12 is used to treat vitamin B12 deficiency (vitamin b12 shots), and cyanide poisoning.  In schilling test, it is given to detect pernicious anemia.

There are two ways of absorption of vitamin B12 in the body from food. First, the hydrochloric acid in the stomach splits vitamin b12 from the protein where vitamin b12 is bound in food. Following this, vitamin B12 attaches to the intrinsic factor; a protein produced by the stomach, and then is absorbed in the body. A condition called pernicious anemia wherein the body cannot produce intrinsic factor prohibits the absorption of vitamin B12 from all food and dietary sources.

Recommended daily intake of vitamin B12 in adults is 2-3 mcg, and its importance is more stressed in pregnant women for the healthy development of the baby. Sources are widely available so deficiencies are unlikely to occur. The most prominent sources of vitamin B12 are meat and its products such as poultry, shellfish, organ meats, eggs, milk and milk products, and fortified foods like soymilk. Therefore, consuming proper amounts from these food groups are necessary to avoid vitamin B12 deficiency anemia or pernicious anemia. Vegans are more susceptible to this disease due to the lack of meat on their diets. Vitamin B12 deficiency symptoms include fatigue, weakness, tingling sensations in the extremities, and loss of balance.