The cyanocobalamin form of Vitamin B12 is synthesized exclusively by bacteria or fungi, and is present in nearly all forms of animal tissue (it is acquired indirectly from bacteria). For humans, dietary sources of vitamin B12 include meat, eggs, and dairy products. There are no plant sources for this vitamin.

In the stomach, dietary vitamin B is liberated from food by the action of stomach acid. Once in the intestines, vitamin B12 must bind to a type of protein known as intrinsic factor. This combination is absorbed through ileum cells in the small intestine, entering the blood stream to be taken up by the liver, bone marrow, and other tissues. Once absorbed, mammalian cells can convert cyanocobalamin to methylcobalamin and adenosylcobalamin (also a coenzyme form of B12). Supplemental vitamin B12 can be given as cyanocobalamin (which must be converted to methylcobalamin) or as the active form of the vitamin – methylcobalamin.

How Does It Work?:
Although there have been questions regarding the bioavailability of orally absorbed vitamin B12 supplements, testing of oral methylcobalamin has demonstrated its ability to increase serum levels of vitamin B12, as well as its clinical efficacy. Functioning as a cofactor for the enzyme methionine synthase, B12 assists in the conversion of total homocysteine (tHcy) to methionine, in the maintenance of the nervous system, and works with folate in the synthesis of DNA and RNA synthesis.* Vitamin B12 also is essential in the synthesis of molecules involved in fatty acid biosynthesis and the production of energy.

Clinical trials have documented significant health benefits for this vitamin.

Heart Health

There is a strong connection between homocysteine levels and cardiovascular health. Homocysteine levels in the blood are influenced by at least three B vitamins: B6, B12, and folate. These nutrients work together in the conversion of homocysteine to methionine or cysteine. Vitamin B12 is an important regulator of this process. Increased intake of vitamin B12 has been associated with reduced homocysteine levels, and may therefore lead to improved heart health. In a 12-week study, 500 mcg of methylcobalamin (given as an intramuscular injection (IM)), was associated with a 37% reduction of homocysteine levels. In a separate study, a combination of 500 mcg (IM) of methylcobalamin plus folate induced a 57% homocysteine reduction in three weeks.

Nervous System Health

Myelin is a fatty substance which covers nerves and nervous system pathways in the brain and spinal cord. Vitamin B12 is a cofactor in the conversion of homocysteine to methionine, which is a precursor to S-adenosylmethionine (SAMe). SAMe, in turn, is involved in the synthesis of myelin basic protein. Therefore, increasing levels of vitamin B12 can lead to increased levels of SAMe, and improved nervous system function. Extremely high doses of methylcobalamin (up to 50 mg/day IM, twice a week) have been used in studies investigating its potential for support of the nervous system. Additionally, the connection between Vitamin B12, folate, and homocysteine levels has been found to have implications for the nervous system, as well as brain and memory function.

The following chart summarizes the benefits of vitamin B12:

 

Ingredient	Benefit
Vitamin B12	Helps maintain healthy homocysteine levels; supports a healthy nervous system; aids in the product of cellular energy

Vitamin B12 Intake and Deficiency

The classic disease associated with vitamin B12 deficiency is pernicious anemia. Caused by a lack of intrinsic factor – which is required in order for vitamin B12 to be absorbed in the intestines – pernicious anemia is characterized by fatigue, weakness, sore tongue, and numbness of the hands and feet. If left untreated, pernicious anemia can lead to nerve degeneration, and eventual paralysis.

Although it can occur in children, most cases of pernicious anemia are diagnosed after age 30. A estimated average prevalence of B12 deficiency is approximately 20% (between 5% and 60%, depending on the definition of deficiency used) in the general population of industrialized countries. The most frequent cause of B12 deficiency, particularly in the elderly, is malabsorption from food (60% of all cases), pernicious anemia (15%-20% of all cases), and insufficient dietary intake. Poor absorption rates in older adults may be related to decreased production of stomach acid. Stomach acid secretions are necessary in order to release B12 from food proteins. Vitamin B12 deficiency may also be related to a vegetarian diet without B12 supplementation, as this vitamin is not found in non-animal based food sources.