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Biotin, also known as vitamin H and coenzyme R, consists of a ureido ring and a thiophene ring with a valeric acid side chain. It has 8 isomers and occurs naturally as just one biotin and is biologically active. In vivo, biotin is mainly stored in the liver at a concentration of 800-3000 ng/g. Blood levels are low. Its main function is to act as a coenzyme in the decarboxylation and deamination reactions. Pharmacologic doses of biotin can lower blood glucose levels in type I diabetics.

1.Biotin deficiency symptoms

Biotin deficiency is seen mainly in people who have been eating raw eggs for a long time. Biotin deficiency can also occur if the diet is deficient in biotin and antibiotics such as sulfonamides are given in large amounts, or if biotin supplementation is neglected with prolonged use of total intravenous nutrition. Deficiency manifestations are mainly characterized by skin symptoms, including thinning of hair, loss of luster, dry skin, scaly dermatitis, and a red rash, which in severe cases can extend to the eyes, nose, and around the mouth. In addition, it is accompanied by loss of appetite, nausea, vomiting, atrophy of the papilla of the tongue, grayish mucous membranes, numbness, depression, fatigue, myalgia, hypercholesterolemia, and electroencephalogram abnormalities.

These symptoms mostly occur after 10 weeks of biotin deficiency. The main site of biotin absorption is the proximal part of the small intestine. At low concentrations, it is actively absorbed by carrier transport; at high concentrations, it is absorbed by simple diffusion. Absorbed biotin is transported via the portal circulation to the liver and kidney for storage. Biotin is also present in other cells, but in smaller amounts. Raw egg whites contain anti-biotin proteins that bind to biotin and inhibit its absorption. A lack of gastric acid can reduce the absorption of biotin.

2.Mechanism of action and metabolism

The transport of biotin to surrounding tissues requires biotin-binding proteins as carriers. Biotin-binding proteins in plasma exist as biotinidase, an enzyme with two high-affinity biotin-binding sites.

Biotin is excreted primarily via the urine. Prior to excretion, about half of the biotin is converted to biotin sulfoxide, di-demethylated biotin, and tetrademethylated biotin before it is excreted. The ratio of biotin, dinitrotoluene and biotin sulfoxide in human urine is approximately 3:2:1. Biotin is also excreted in breast milk, but in very small amounts. Since intestinal bacteria can synthesize biotin, it is not easy to accurately determine the amount of biotin needed.

The Chinese Nutrition Society (CNS) proposed an AI value for Chinese residents in 2000, which is 30 μg/d for adults.The nutritional status of biotin can be evaluated by determining the blood and urine biotin content, plasma concentration of odd carbon fatty acids, and urinary excretion of relevant metabolites. Biotin is widely found in natural foods. Cheese, beef liver, and soybean meal are the most abundant, followed by eggs. Refined cereals and most fruits are less abundant.

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