Volume : VI, Issue : IX, September - 2017

VITAMIN B12 DEFICIENCY

Rossen Mihaylov, Blagovesta Pencheva, Stanislava Zlateva

Abstract :

 The term vitamin B12 includes several chemical compounds similar in chemical structure (1,2,3,4). There are 4 known kinds of vitameres of vitamine B12: (a) cyanocobalamin, which is metabolized in the body to an active coenzyme; (b) hydroxocobalamin which is not normally present in the human body; (c) adenosylcobalamin (adoB12), an active cofactor; and (d) methylcobalamin (MeB12), an enzymatically active cofactor (1,3). In the body, vitamin B12 is mostly stored as adoB12 in the liver. Vitamin B12 is very stable at high temperature, while in strongly acidic and strongly alkaline conditions it loses its activity. Its levels are negatively affected by alcohol and estrogens. Serum vitamin B12 binds to proteins known as transcobalamins. The majority of the vitamin, approximately 80%, is transported on the inactive TCI (also called haptocorrin). The active transport protein for vitamin B12 is transcobalamin II (TCII), which carries about 20% of the vitamin in the circulation (1,4,5). Holo–transcobalamin (holo–TC) is TCII with attached cobalamin, which delivers vitamin B12 to the cells. The low serum vitamin B12 concentration can be associated with a deficiency of TCI. Methylmalonic acid and homocysteine ​​are indicators of the status of vitamin B12 in the body cells.  Methylmalonic acid is considered to be a specific indicator of cobalamin metabolism (5,6,7). Homocysteine ​​is a derivative of methionine which is supplied through the proteins in the food. The body converts the greater part of homocysteine ​​back to methionine with the help of vitamin B12 (7,8). In case of B12 deficiency, homocysteine ​​levels increase, because this reaction cannot take place. Normal serum levels of homocysteine ​​are from 2.2 to 13.2 μmol / l. Vitamin B12 is not synthesized by multicellular or unicellular eukaryotes (1,5,8). All of the substrate cobalt–corrin molecules, from which B12 is made, are synthesized by bacteria. The human body has the ability to convert any form of B12 to an active form, by means of enzyme action. Animals store vitamin B12 in the liver and muscles. Meat (lamb, veal, beef and turkey), liver, eggs, cheese and milk are sources of vitamin B12. As vegetarian diets generally include high content of folic acid, elevated levels of homocysteine ​​in vegetarians are typically due to the low intake of B12 (1,4,6). 

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Article: Download PDF   DOI : 10.36106/ijsr  

Cite This Article:

Rossen Mihaylov, Blagovesta Pencheva, Stanislava Zlateva, VITAMIN B12 DEFICIENCY, INTERNATIONAL JOURNAL OF SCIENTIFIC RESEARCH : Volume-6 | Issue-9 | September-2017

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