Vitamin B12 is crucial for proper human metabolism, the creation of deoxyribonucleic acid (DNA), and red blood cells (RBCs). Another role involves the maintenance of healthy nerve tissue. Although this vitamin is regularly available in animal products and humans require a relatively small amount for normal health, there are situations where supplementation is necessary. These conditions include pregnancy, digestive issues, and pure vegetarian diets. Several forms of this vitamin are available with varying levels of effectiveness.
What is Vitamin B12?
Vitamin B12 is a term given to a class of water soluble chemicals that share structural similarity and physiologic activity in the body. These chemicals share a common complicated core of nitrogen and cobalt (called cobalamin) but differ in the attachment of other constituent molecules to the cobalt part. While many others exist in nature, there are four types that humans can utilize:
- Cyanocobalamin (CN-Cbl)
- Hydroxycobalamin (OH-Cbl)
- Adenosylcobalamin (AdeCbl)
- Methylcobalamin (MeCbl)
The natural origin of dietary B12 is ultimately bacteria. Many bacteria species produce this vitamin which is then ingested by animals. Humans then eat animal products to get their daily requirements. At one time it was thought that plants also created ample B12 but researchers have since shown this to not be the case. Plants may create B12-like molecules that look like the vitamin but lack and even hinder B12 activity in humans. This vitamin is created by bacteria in the human colon but it's not absorbed and thus is excreted in the feces. In some studies it was found that adequate vitamin B12 was obtained when fruits and vegetables were not washed and B12 producing bacteria were left on them.
Challenges with Synthetic Forms of B12
Cyanocobalamin (CN-Cbl) is cheap and easy to create and thus, the most commonly found form of B12 in supplements. Not found in nature, the challenge with CN-Cbl is that in order for it to have biological activity it must be processed in the liver in a pathway requiring several steps. These steps deal with the attached cyanide and require an important antioxidant called L-glutathione. L-glutathione (a tri-peptide made from the amino acids glutamic acid, cysteine, and glycine) is often already in short supply due to its use in other important missions. This process makes the liver work harder so those with impaired liver function may not efficiently convert CN-Cbl to a usable form. Also, while the cyanide released is minute, those with impaired or stressed liver function may possibly experience compounded effects like increased nausea. Therefore, this form of B12 is contraindicated in chronic hepatitis or in pregnant women already experiencing morning sickness. Hydroxycobalamin (OH-Cbl) is another inexpensive form that does not exhibit biological activity until liver manipulation.
More Absorbable Forms of B12
Adenosylcobalamin (AdeCbl) and methylcobalamin (MeCbl) are active forms that are less stable and more expensive but easier to absorb and readily used by the body. Documented research exists supporting their efficacy in conditions like liver disease, sleep disturbances, diabetic neuropathy, and anemia.
Human Requirements
Humans require about 1-2 mcg of vitamin B12 a day. The average American diet affords about 5-30 mcg, of which about 2-3 micrograms are actually absorbed through a complex pathway, then stored in the liver. The liver may keep a stockpile of 2-3 mg. Under deficient conditions this stockpile may last up to two years before signs and symptoms occur. Lack of this vitamin may occur due to digestive challenges like gastritis or inflammatory bowel disease, pernicious anemia, and poor dietary choices.
Supplementary Resources
- K. Okuda et al., “Intestinal absorption and concurrent chemical changes of methylcobalamin.,” The Journal of laboratory and clinical medicine 81, no. 4 (1973): 557.
- J. F. Adams et al., “Absorption of cyanocobalamin, coenzyme B 12, methylcobalamin, and hydroxocobalamin at different dose levels.,” Scandinavian journal of gastroenterology 6, no. 3 (1971): 249.
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