According to MedlinePlus, vitamin B12 is a nutrient found in meats, fish and dairy products. It can also be synthesized in laboratories for use in supplements.
According to MedlinePlus, supplementation of vitamin B12 is used to treat and prevent vitamin B12 deficiency. It is also used to treat pernicious anemia and memory loss. The vitamin has also been used to treat heart disease, male infertility, diabetes, depression, mental disorders, asthma, allergies and certain skin infections. The supplement form of the nutrient can be taken orally. It is also available in lotion or gel form to be applied directly to the skin.