Biotin, also known as vitamin H, is of great importance for the biochemistry of the human organism. As a prosthetic group of mitochondrial enzymes (carboylases), biotin plays a central role as a CO2-carrier in important metabolic reactions such as gluconeogenesis, synthesis of fatty acids and metabolism of amino acids. Furthermore, biotin influences the growth and maintenance of blood cells, sebaceous glands, skin, hair and nails. Next to the free form of biotin, the biotin linked to lysin, also known as biocytine, can also be utilized as a vitamin source by the body, after cleavage from the protein by the enzyme biotinidase.
In nature, biotin is very common. It can be found in bacteria and mushrooms, as well as in higher plant life and animal tissue - especially in liver and kidney. However, the biotin availability in some food is very slim. Amounts worth mentioning can only be found in yeast, soya beans, nuts, cauliflower, lentils, oats, wheat germ and in egg yolk whereas fruits, milk products and most vegetables only contain small amounts. Solely, the amount of biotin is not the decisive factor, but rather the bioavailability. The bioavailability varies very strongly and depends on the kind of food and also on the extent to which biotin is protein-bound. Whereas, for example, in plants, biotin is available in the free form, food coming from animals contains mostly protein-bound biotin. Only after proteolytic reduction in the small intestine followed by a cleavage with intestine (pancreas)-biotinidase is the biotin available in the free absorbable form.
Biotin which is synthesized endogenously by flora of the intestine is not reabsorbed in the colon, but is stored as protein-bound biotin in the bacteria of the intestine and is thus not available to cover the biotin requirement of the organism. The treatment of food also causes losses in biotin. Wheat, as a whole grain, contains 4 times as much biotin as all-purpose flour (Type 405). The alimentary utilization of biotin is estimated at 50 %, so that a biotin deficiency can easily result. Malnutrition as well as an inherited disorder in biotin metabolism (singular or multiple deficiency in carboxylase, biotinidase deficiency) can lead to a biotin deficiency. Furthermore, circumstances of life, where an increased biotin demand exists (pregnancy, nursing, athletic activities, pathological conditions) may cause a biotin malnutrition. A variety of disorders on hair, skin and nails are the medically relevant consequences of a biotin deficiency. The symptoms range from brittle, splintered fingernails to different forms of alopecia to scaly erythematous and seborrheic dermatitis. Animals have also been observed with similar illnesses, ranging from larger skin detachments, epidermal crust development, as well as a hyper- and parakeratosical change in mucous membrane.
