Biotin ( Vitamin B7) - Benefits, Deficiency Symptoms And Food Sources
Biotin is a water-soluble vitamin, generally classified as a B-complex vitamin. Biotin was first isolated in 1936 and synthesised in 1943. Dr. Helen Parsons observed symptoms such as eczema and hair loss in rats being fed a diet including raw egg white. The symptoms were cured by adding egg yolk to the diet of the affected, animals. The corrective factor was isolated and termed 'biotin'.
The substance in raw egg white was identified to be a biotin antagonist, which prevented its absorption. The substance was called avidin and it could be easily destroyed by heat.
Biotin is required by all organisms but can only be synthesised by bacteria, yeast, molds, algae and some plants. The bacteria in our intestinal tract also synthesise biotin, which can be absorbed in parts from the intestinal tract. Biotin is stored in minute amounts in the metabolically active tissues such as the kidney, liver, brain and adrenal. There are no known toxic effects from biotin.
A relatively simple compound, soluble in water, biotin is stable to heat, light and acids, but somewhat sensitive to alkalis and oxidising agents. In tissues and in foods, it is usually combined with protein.
Functions of biotin
Biotin plays an important role in metabolism as a coenzyme that carries carbon dioxide. This role is critical in the energy cycle in carboxylation and decarboxylation reactions. It participates in carbon dioxide fixation reactions that transfer carbon dioxide from one compound to another. In the energy cycle, biotin fixes carbon dioxide on to a 3-carbon compound to form 4-carbon compound, which keeps the energy cycle going. It is required in the energy cycle and is thus essential for the production of energy from glucose. Carboxylation reactions involving biotin are also a part of the following metabolic, pathways:
Biotin is thus essential for the metabolism of carbohydrates, fats and proteins, as well as nucleic acids such as DNA and RNA.
Daily allowances of biotin
The minimum Recommended Dosage Allowance of biotin is 50 to 200 mcg.
Rich sources of biotin
Biotin is widely distributed in foods but few foods have high concentrations. Milk, liver, egg yolk, legumes, nuts and a few vegetables are the most important sources of biotin in human diets. The bio availability of biotin varies considerably among different foods. This is because biotin is bound to protein to form complexes in different foods. The availability of biotin from these complexes depends upon the digestibility of that complex.
The availability of biotin from raw egg presents a typical case of protein-biotin complexes, which led to its discovery. Egg white contains a protein called avidin (antivitamin). Avidin binds biotin to form a complex, which is resistant to digestion. Biotin from raw egg is thus not available to the body. Cooking denatures avidin and inactivates its biotin-binding capacity. Biotin from cooked eggs is easily absorbed from the intestine.
Deficiency of biotin
Since biotin is widespread in foods - it is also available from intestinal synthesis, and the requirement is minute - natural biotin deficiency is rare. However, biotin deficiency can be induced by feeding large quantities of raw egg white which contains avidin, a protein that binds biotin and prevents its absorption in the body. Cooking the egg white inactivates avidin. Therefore consumption of cooked egg has no effect on biotin absorption in the body. Symptoms of deficiency include loss of appetite, nausea, hair loss, and scaly red rash around the eyes, nose, mouth and genital area. Neurological symptoms include depression, lethargy, hallucination and numbness and tingling sensation in the hands and feet.
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