Vitamin B12, also called cobalamin, is a water-soluble vitamin that supports the function of the nervous system and the formation of healthy red blood cells. The term “B12 strain” is often used, but this reflects a misunderstanding. The confusion likely stems from the fact that the vitamin exists in different chemical forms and is produced by various strains of microorganisms.
The Different Forms of Vitamin B12
Vitamin B12 is not a single molecule but a collection of compounds called cobalamins. All forms have a complex chemical structure with a cobalt ion at the center. The differences between them lie in the small molecule, or ligand, that is attached to this cobalt ion. There are four primary forms of B12 relevant to human health: cyanocobalamin, methylcobalamin, adenosylcobalamin, and hydroxocobalamin.
Cyanocobalamin is a synthetic form of B12 frequently used in dietary supplements and to fortify foods because it is chemically stable and less expensive to produce. It contains a cyanide molecule, which the body must remove and convert into an active form. The amount of cyanide is minuscule and considered safe.
In contrast, methylcobalamin and adenosylcobalamin are two naturally occurring, active forms of B12 found in food sources. These active forms function as coenzymes in the body. Methylcobalamin is the most bioavailable form, playing a part in the function of the liver, brain, and nervous system. Adenosylcobalamin is a natural coenzyme form important for protecting mitochondria, the powerhouses of cells, and helping them produce energy. Hydroxocobalamin is another natural form, produced by bacteria, that the body converts into the active forms.
The True Origin of Vitamin B12
Vitamin B12 is unique because it is synthesized exclusively by certain bacteria and archaea. Neither plants nor animals have the genetic instructions or enzymes needed to produce this complex molecule.
In ruminant animals like cows and sheep, bacteria in their digestive systems produce vitamin B12, which is then absorbed by the animal. This B12 accumulates in their tissues and milk, which is why animal products like meat, eggs, and dairy are primary dietary sources for humans. In aquatic environments, B12 made by bacteria is consumed by phytoplankton and moves up the food chain into fish and seafood.
While some plant foods like fermented products or certain seaweeds may contain B12, it is due to their association with these B12-producing microorganisms. The B12 synthesized by bacteria in the human colon is not absorbed because the absorption site is located further up in the small intestine. This makes it necessary to obtain B12 from external sources through diet or supplementation.
Choosing a B12 Supplement
Cyanocobalamin is the most common and affordable supplement option, valued for its stability. However, the body must convert it into an active form, a process that can be less efficient for some individuals. Methylcobalamin is a bioavailable choice beneficial for supporting neurological health. Adenosylcobalamin is an active form that plays a direct role in cellular energy production, making it a consideration for combating fatigue. Hydroxocobalamin, often administered via injection, stays in the body for longer periods and is used to address serious deficiencies.
Certain genetic factors can influence which form of B12 is most suitable. For example, people with a common mutation in the MTHFR gene may have difficulty with the conversion process required for cyanocobalamin. For these individuals, a pre-activated form like methylcobalamin might be more effective. Consulting with a healthcare provider can help determine the most appropriate form and dosage based on individual health needs.