Names of B12 Vitamins

Vitamin B12 is an essential nutrient, meaning that the human body cannot produce sufficient amounts of it, so people must get it from dietary sources, such as protein-rich meat, poultry, fish, eggs and dairy products, from fortified foods such as cereals, or from supplements. Vitamin B12 assists with red blood cell formation, nervous system functioning and DNA synthesis. Multiple forms of vitamin B12 exist, and the group of compounds is collectively called "cobalamins," due to the presence of the mineral cobalt.

The Stable Form of B12

Cyanocobalamin is the form of vitamin B12 that is usually used in supplements and in fortified foods because it is stable, meaning that it keeps its properties and structure even during processing and exposure to different temperatures. The body can only absorb cyanocobalamin through the small intestine, however, when a protein called intrinsic factor is present. Intrinsic factor attaches two vitamin B12 molecules together, preparing them for transport to the bloodstream, and converting them to their active, usable form. People who cannot absorb cyanocobalamin because of the lack of this important protein may suffer from vitamin B12 deficiency.

Active Forms of Vitamin B12

Methylcobalamin, known as methyl-B12, and 5-deoxyadenosylcobalamin, known as coenzyme B12, are the active forms of vitamin B12 that can perform their vital functions in the body. They are naturally bound to protein foods, but are released in the stomach by hydrochloric acid and an enzyme called protease. Intrinsic factor then helps these forms of B12 get absorbed into the bloodstream. Once absorbed, methyl-B12 appears to be the main form of B12 seen in the blood, and coenzyme B12 is mostly stored in the liver.

Inactive Forms of Vitamin B12

The bloodstream and tissues contain a third form of vitamin B12, which collectively includes all vitamin B12 analogs, called noncobalamin corrinoids. These analogs have little or no activity in the body. The presence of these compounds has made it difficult to measure active vitamin B12 levels in the bloodstream, because they resemble the active forms of vitamin B12 in blood tests.