Biotin, also known as vitamin H or B7, is a water-soluble B-complex vitamin which 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 cofactor in the metabolism of fatty acids and leucine, and it plays a role in gluconeogenesis.

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 is also helpful in maintaining a steady blood sugar level. Biotin is often recommended for strengthening hair and nails. Consequently, it is found in many cosmetics and health products for the hair and skin.

Biotin deficiency is rare, as intestinal bacteria generally produce an excess of the body's recommended daily requirement. For that reason, statutory agencies in many countries (e.g., the Australian Department of Health and Aging) do not prescribe a recommended daily intake of Biotin.

Dietary

Biotin is widely distributed in a variety of foods although at low concentrations. Estimates are that the typical U.S. diet provides roughly 40 µg/day. There are only a couple of foods which contain biotin in large amounts, including royal jelly and brewer's yeast. The best natural sources of biotin in human nutrition are liver, legume, soybeans, Swiss chard, tomatoes, romaine lettuce, and carrots. These sources of biotin include almonds, eggs, onions, cabbage, cucumber, cauliflower, goat's milk, cow's milk, raspberries, strawberries, halibut, oats, and walnuts. The most important natural sources in feeding nonruminant animals are oilseed meals, alfalfa, and dried yeasts. The biotin content of food varies and can be influenced by factors such as plant variety, season, and yield (endosperm-to-pericarp ratio).

Uses

Hair problems

Biotin supplements are often recommended as a natural product to counteract the problem of hair loss in both children and adults. The signs and symptoms of biotin deficiency include hair loss which progresses in severity to include loss of eye lashes and eye brows 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.

Cradle cap (seborrheic dermatitis)

Children with a rare inherited metabolic disorder called phenylketonuria (PKU; in which one is unable to break down the amino acid phenylalanine) often develop skin conditions such as eczema and seborrheic dermatitis in areas of the body other than the scalp. The scaly skin changes that occur in people with PKU may be related to poor ability to use biotin. Increasing dietary biotin has been known to improve seborrheic dermatitis in these cases.

Diabetes

Diabetics may also benefit from biotin supplementation. In both insulin-dependent and non-insulin-dependent diabetes, 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.