Biotin is a water-soluble vitamin that is found in foods in two forms: free vitamin and protein-bound coenzyme form (biocytin). It was discovered during World War II, when chicks fed diets that were high in raw egg white developed skin rashes and lost the down feathers around their eyes. When egg yolk was added to their diet, these symptoms disappeared.
Absorption
In biocytin, biotin bonds with lysine, an amino acid type, in a protein. In the small intestines, biotinidase (an enzyme) breaks the biotin from the protein, releasing the free vitamin and making it absorbable.
Function
Biotin is an essential cofactor for four carboxylase enzymes that are necessary for aerobic respiration in cells. In the citric acid cycle―an important step in aerobic respiration―biotin carboxylase reactions create more oxaloacetate, an essential compound to start the cycle. If biotin is missing, the citric acid cycle would not run effectively, resulting in a buildup of lactate, a byproduct of anaerobic glycolysis (sugar breakdown). This will cause muscle fatigue and cramps during endurance exercise.
Sources
Good sources of biotin include eggs (with yolk), liver, romaine lettuce, tomatoes, almonds, walnuts and dairy products.
Daily Intake
Adults need about 30 micrograms of biotin daily, and there is no current upper limit on how much can be taken. Children and teenagers between 9 and 19 years old require between 20 and 25 micrograms a day.
Deficiency
Biotin deficiency is uncommon among adults but it sometimes occurs in infants. Common symptoms of biotin deficiency in infants who lack biotinidase include skin rash, hair loss, convulsions, impaired growth, seizures and lack of muscle coordination.
References
- "The World's Healthiest Foods, Essential Guide for the Healthiest Way of Eating": George Mateljan; 2006
- "Persepctives in Nutrition": Gordon Wardlaw, Margaret Kessel; 2002
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