Biotin
Biotin is another B vitamin with which most people aren't familiar, even though its discovery dates back to the 1930s. The nutrient plays an important role as a coenzyme in several metabolic reactions. One such reaction is crucial in the pathway that releases energy from carbohydrate. Other reactions include making new glucose and fatty acids, and the breakdown of amino acids.
Biotin is another B vitamin that you can find in a wide variety of foods, although the amounts are limited. Good sources include liver, egg yolks, whole grain cereals, soy flour, and yeast. One interesting interaction occurs with raw eggs, which contain the protein avidin. Avidin grabs the biotin, also present in the egg, and-prevents the intestine from absorbing it. Cooking the egg causes the proteins to uncoil and not work as they should, and, in the case of avidin, it's just as well. In virtually all the documented deficiency cases, eating raw eggs was the reason for the problem. As long as you don't eat two dozen raw eggs every day, the amount experts say produces the deficiency, you don't have much to worry about.
Scientists had known that intestinal bacteria produce the vitamin, making it available to humans. However, they now believe that this is not a significant source of the vitamin. The new DRI for biotin is 30 micrograms for both men and women, and surveys show that Americans consume 28 to 42 micrograms per day of this nutrient. The vitamin is relatively nontoxic, with doses as high as 60 mg for six months causing no ill effects.
Researchers were the first to see biotin deficiency in humans when they fed volunteers a biotin-deficient diet in the 1940s. Within five weeks of the deficient diet, all volunteers had changes in mental status, nausea and anorexia, and numbness and tingling. In two more weeks, they developed dermatitis on their arms and legs. Biotin injections reversed all the symptoms. If the deficiency had been allowed to progress, however, the volunteers would have lost their hair and suffered from weakened immunity. Infants may be born with a genetic defect, organic acidemia, that produces biotin deficiency. Without receiving biotin injections, the infants would soon die.