Vitamin H (biotin)

Biotin is also called vitamin H or vitamin B7. It is a water-soluble B-complex vitamin (vitamin B7) that is composed of an ureido (tetrahydroimidizalone) ring fused with a tetrahydrothiophene ring. A valeric acid substituent is attached to one of the carbon atoms of the tetrahydrothiophene ring. Biotin is a co-enzyme in the metabolism of fatty acids and leucine, and it plays a role in gluconeogenesis.

Biotin is consumed from a wide range of food sources in the diet, however there are few particularly rich sources. Foods with a relatively high biotin content include raw egg yolk (however, the consumption of egg whites with egg yolks minimizes the effectiveness of egg yolks biotin in one's body), liver, some vegetables, and peanuts. The dietary biotin intake in Western populations has been estimated to 35 to 70 µg/d. Biotin is also available from supplements. Biotin is necessary for cell growth, the production of fatty acids, and the metabolism of fats and amino acids. It plays a role in the citric acid cycle, which is the process by which biochemical energy is generated during aerobic respiration. Biotin not only assists in various metabolic reactions but also helps to transfer carbon dioxide. Biotin may also be helpful in maintaining a steady blood sugar level. Biotin is often recommended for strengthening hair and nails. As a consequence, it is found in many cosmetics and health products for the hair and skin, though it cannot be absorbed through the hair or skin itself.
Biotin deficiency is rare, because, in general, intestinal bacteria produce biotin in excess of the body's daily requirements. For that reason, statutory agencies in many countries, for example the USA and Australia, do not prescribe a recommended daily intake of biotin. However, a number of metabolic disorders in which an individual's metabolism of biotin is abnormal exist; in these disorders, mega doses of biotin, far higher than the average daily intake from food, in general, can mitigate symptoms and correct the underlying metabolic disturbance.

Biotinidase deficiency, a rare inherited condition, is often associated with seizures, skin disorders, bald spots,
hearing loss, visual disturbances, and developmental delay. Biotin supplements may improve symptoms of the inherited form of biotinidase deficiency, seen most commonly in people from Saudi Arabia. Pregnant women tend to have a high risk of biotin deficiency. Research has shown that nearly half of pregnant women have an abnormal increase of 3-hydroxyisovaleric acid, which reflects reduced status of biotin. Numbers of studies reported that this possible biotin deficiency during the pregnancy may cause infants' congenital malformations such as cleft palate. The signs and symptoms of biotin deficiency include hair loss that progresses in severity to include loss of eyelashes and eyebrows in severely deficient subjects. Some shampoos are available that contain biotin, but it is doubtful whether they would have any useful effect, as biotin is not absorbed well through the skin. Diabetics may also benefit from biotin supplementation. In both insulin-dependent and non-insulin-dependent diabetics, supplementation with biotin can improve blood sugar control and help lower fasting blood glucose levels. In some studies the reduction in fasting glucose exceeded 50 percent. Biotin can also play a role in preventing the neuropathy often associated with diabetes, reducing both the numbness and tingling associated with poor glucose control. However, more research is needed to know for sure whether biotin can help treat this condition.