Regular vitamin B12, or cyanocobalamin, must be absorbed and then converted by the body to an active form to be of use. Due to genetic variations, some individuals may have trouble converting B12 to the active forms.

Adenosylcobalamin, also known as dibencozide, is the active form of B12 that is used by the mitochondria, the energy powerhouse in each cell. Vitamin B12 is an essential vitamin found in foods such as meat, fish, and dairy products. Although the body can store vitamin B12 in the liver, deficiency may result from difficulties in converting cyanocobalamin to active vitamin B12. In food, B12 is bound to protein, and hydrochloric acid (HCl) in the stomach along with Intrinsic Factor (IF) are required for humans to adequately absorb this vitamin. Insufficient amounts of either HCl or IF may lead to inadequate levels of B12. Additionally, vegetarians and especially vegans may require additional B12 that they don't get from their diet.*