Biotin is a water-soluble B-vitamin that contains sulfur. The biotin molecule contains three asymmetric carbon atoms, and therefore eight different isomers are possible. Of these isomers, only the dextrorotatory (+) d-biotin possesses biotin activity as a coenzyme. Biotin functions as a coenzyme for four carboxylases acetyl-CoA carboxylase, pyruvate carboxylase, propionyl-CoA carboxylase, and b-methylcrotonyl-CoA carboxylase. Acetyl-CoA carboxylase forms malonyl-CoA from acetyl-CoA in the initiation of fatty acid synthesis.
Pyruvate carboxylase is an essential enzyme in gluconeogenesis, the formation of glucose from amino acids and fats. Propionyl-CoA carboxylase is involved in the metabolism of the amino acids isoleucine, threonine, methionine, valine, and odd-chain fatty acids. b-Methylcrotonyl-CoA carboxylase functions in the catabolism of the amino acid leucine.
Thus, biotin is required for the synthesis and degradation of fatty acids and gluconeogenesis as well as protein degradation. Biotin deficiency is rare in humans, but the deficiency occurs in two different situations: the consumption of large amounts of raw egg whites over long periods and total parenteral nutrition without biotin supplementation. Egg whites contain the protein avidin, which binds biotin and prevents its absorption. Avidin is denatured by cooking. Gastrointestinal disorders such as inflammatory bowel disease and achlorhydria may result in impaired biotin absorption. The symptoms of biotin deficiency include lethargy, depression, hallucinations, muscle pain, paresthesia in extremities, anorexia, nausea, hair loss, and scaly red dermatitis. The IOM has established recommendations for biotin as AIs because sufficient scientific evidence is not available for estimating an average requirement for biotin. The AI for biotin is 30 μg/d for men and women aged 19 years and older. Biotin is widely distributed in foods. Liver, egg yolks, soybeans, and bakers and brewer’s yeasts are relatively rich sources. Toxicity of biotin has not been reported. Large doses of biotin (up to 200 mg/d) have been given daily to individuals with inherited disorders of biotin metabolism without side effects.103 Due to the lack of the evidence of adverse effects, ULs for intake of biotin have not been set by the IOM. Biotin is involved in energy metabolism; thus, biotin might have some effects on physical activity. Research has not been conducted regarding biotin status in athletes and effects of biotin supplementation on exercise performance. There are no specific biotin recommendations for athletes.
