Vitamin B12, also called cobalamin, is a water-soluble vitamin that has a key role in the normal functioning of the nervous system via the synthesis of myelin (myelinogenesis),(1, 2) and in the maturation of developing red blood cells in the bone marrow. It is involved in the metabolism of every cell of the human body: it is a co factor in DNA synthesis, fatty acid metabolism, and amino acid metabolism.(3) Vitamin B12 deficiency can potentially cause severe and irreversible damage, especially to the brain and nervous system.(4) At levels only slightly lower than normal, a range of symptoms such as fatigue, lethargy, depression, poor memory, breathlessness, headaches, and pale skin, among others, may be experienced, especially in elderly people (over age 60)(5, 6) who produce less stomach acid as they age, thereby increasing their probability of B12 deficiencies.(7) Vitamin B12 deficiency can also cause symptoms of mania and psychosis.(8) Vitamin B12 deficiency is most commonly caused by low intakes, but can also result from malabsorption, certain intestinal disorders, low presence of binding proteins, and use of certain medications. Vitamin B12 is rare from plant sources, so vegetarians are more likely to suffer from vitamin B12 deficiency. Infants are at a higher risk of vitamin B12 deficiency if they were born to vegetarian mothers. The elderly who have diets with limited meat or animal products are vulnerable populations as well. Vitamin B12 deficiency may occur in between 40% to 80% of the vegetarian population who are not also consuming a vitamin B12 supplement. (9) In Hong Kong and India, vitamin B12 deficiency has been found in roughly 80% of the vegan population as well.(10)