Vitamin B12 (Cobalamin).
Vitamin B12 is also called cobalamin or cyanocobalamin, since it  contains cobalt in its molecule structure. Cobalamin, as all the members of vitamin B complex vitamins, is a water-soluble coenzyme and promotes metabolism within the cells by participating in a number of important biochemical reactions.
Vitamin B12 helps in cell division, formation of red blood cells, synthesis of DNA, metabolism of carbohydrates and fats, production of protein, the proper function of the immune system and the maintenance of the central nervous system. Cobalamin is very important for the synthesis of myelin, a protein that surrounds and insulates nerve cells.
In combination with folic acid and pyridoxine, vitamin B12 may prevent angina, heart coronary disease and stroke by decreasing the levels of the amino acid homocysteine in the blood stream.
Vitamin B12 is absorbed in the small intestine with the help of a glycoprotein which is produced in the parietal cells of the stomach and it is called intrinsic factor. Cobalamin is excreted in the bile in the small intestine and it is readily reabsorbed. The function is described as "enterohepatic circulation". In fact, reabsorption is the
mechanism that can delay for more than twenty years the development of deficiency to show, in people with prolonged periods of diet poor in cobalamin. Vitamin B12 is synthesized by certain bacteria in the large intestine but it cannot be absorbed, since the production of the vitamin takes place far beyond the area of the small intestine, where absorption can occur.
Small amounts of vitamin B12 are stored in the liver and kidneys.
Sources of vitamin B12 (cobalamin).
Vitamin B12 is found in eggs, meat, poultry, shellfish, fish, dairy products, fortified soy milk, margarines and cereals. Natural non-animal sources of vitamin B12 exist but they are highly variable in their content. For this reason, they cannot be considered reliable sources. What is more, the amounts of cobalamin contained in vegetables can hardly be absorbed within humans' gastrointestinal track. Thus, vegetarians may get vitamin B12 deficient. Infants, children, elderly, people with pernicious anemia or gastrointestinal conditions and pregnant or lactating women have increased requirements for cobalamin and they may benefit from relevant supplementation. In fact, food supplements, containing vitamin B12 are available and they can be very useful, especially to vegetarians and people included in the above categories. Try the following
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Vitamin B12 (cobalamin) deficiency and toxicity.
As it has been already mentioned, vitamin B12 can be obtained primarily from animal products. Thus, vegetarians, who do not take proper amounts of cobalamin, are susceptible to deficiency.
Some researchers believe that deficiency in cobalamin is mainly a matter of proper absorption rather than adequate dietary intake. Alcoholism can result in vitamin B12 reduced absorption.
Low levels of cobalamin can cause anemia, fatigue, weakness, menstrual irregularities, burning and sore tongue, abdominal discomfort, constipation, poor immune function, loss of appetite,
unintentional
weight loss and neurological symptoms, such as loss of balance, numbness and tingling in the limbs. Studies have given evidence that low levels of cobalamin may be linked to certain conditions, such as diabetic neuropathy, AIDS, reduced male fertility, multiple sclerosis and mental disorders, such as dementia, depression and confusion.
No toxicity incidents have been reported. In fact, water-soluble vitamins cannot accumulate within the body and cause such problems, because excessive amounts are easily excreted in the urine. In certain cases, high doses of vitamin B12 may cause or worsen acne vulgaris.
Recommendations for vitamin B12 (cobalamin).
The vitamin B12 recommended dietary allowances (RDAs) for children are 0.9-1.8mcg/day and for adults 2.4mcg/day. For pregnant and breastfeeding females the relevant figures are 2.6 and 2.8mcg/day respectively. The above doses are recommended, in order to meet the minimum nutritional requirements.
In general, for adults, a daily dose of 350mcg of cobalamin is safe and well accepted.
It has to be bore in mind that boiling destroys cobalamin contained in milk.
Supplementation of any single vitamin B for a long period of time, may lead to significantly imbalanced state of other members of the complex. Thus, a full range of additional supplementation for vitamin B complex is recommended. |
