Vitamin B12 with its chemical names Cobalamin, Cyanocobalamin, and Methylcobalamin is the most potent vitamin and is also called anti-pernicious anemia vitamin. It was previously designated as extrinsic or food factor of Castle. Cobalamin was isolated in 1948 and was synthesized in 1973.
Chemistry: It is the naturally occurring organic compound and contains cobalt. It is water soluble, deep red, tasteless crystalline compound. It is heat stable at neutral pH but not at alkaline pH.
This vitamin is synthesized by microorganisms. Liver and kidney are its chief sources but it also occurs in milk, eggs, and fish. Another source in man may be the bacteria present in the intestine but it is quite variable. Although not expected to be present in the plant products, a certain amount of B12 is present in the legumes which have become contaminated with bacteria which has to synthesize it.
In the body vitamin B12 taken in any form is converted into coenzymes B12 which are called cobamides. These enzymes do not contain –CN or –OH group but contain one of the following two groups attached to the cobalt atom.
- Adenine nucleoside: This group is added in the mitochondria forming the active ingredient deoxyadenoslycobalamine. This is a cofactor for the mitochondrial mutase which catalyzes an important reaction necessary for carbohydrate and lipid metabolism.
- Methyl Group: This group is added in the cytosol to cobalt atom forming methylcobalaime; it is the coenzyme for methionine synthase which is essential for the normal folic acid metabolism. The folic acid and vitamin B12 interaction are important for the synthesis of purines, pyrimidines, and DNA. Red blood cells suffer most in B12 deficiency because of their high turn over.
Megaloblastic Anemia: The anemia of vitamin B12 deficiency is really due to tissue folic acid deficiency. Vitamin B12 is in the form of methylcobalamin and it is a coenzyme for the reaction which forms methionine and releases THFA which serves as a carbon unit. This carbon unit plays a vital role in supplying purines and pyrimidines and DNA to the cells undergoing mitosis. In case of this vitamin deficiency there results in non-maturation of nuclei and failure of DNA formation resulting in bigger red blood cells production. The neurological symptoms may arise due to a decrease in methionine.
- Pernicious Anemia: In this disease also known as Addisonian anemia, the primary defect is the absence of intrinsic factors in the gastric juice. It shows severe anemia clinically along with mild jaundice, anorexia, flatulence, and diarrhea. There is also evidence of ineffective erythropoiesis and with very severe deficiency pancytopenia may also be seen.
- Gastric Resection and Intrinsic Factor Loss: This operation results in loss of the important intrinsic factor.
- Pancreatectomy: In the absence of pancreatic proteases absorption of B12 is decreased.
- Dietary Lack
- Infestation with fish tapeworm (Diphyllobothrium latum)
- Blind loop syndrome
- Hereditary Malabsorption
- Drugs: These include colchine, neomycin, ethanol, and KCL etc.
There are as such no ill effects if vitamin B12 if it is ingested in high quantity.