W

Figure 8.42. Biotin binding carbon dioxide.

O O C02

II II 1 Biotin

Pyruvate ATP ADP +Pi Pyruvate carboxylase

0 OO

II II II

Oxalacetate

Figure 8.43. Carboxylation of pyruvate producing oxalacetate.

3.10.4 Biotin Deficiency. Relative to many of the vitamins, it is easy to induce a biotin deficiency by feeding volunteers raw egg white. Avidin, a basic protein found in egg white, forms salt linkages with acidic biotin and prevent its transport across the intestinal barrier. Cooked egg white is not a problem. Because biotin is found in the yolk, eating whole raw egg will not induce a deficiency. Deficiencies also were caused in patients on total parenteral nutrition (TPN) because biotin was not included in the early formulations. Symptoms include dermatitis, loss of hair color, and central neurological effects.

3.10.5 Hypervitaminosis Biotin. None has been reported in humans and there are no Tolerable Upper Intake Levels.

3.10.6 Dietary Reference Intakes. These have been difficult to determine. There has been some speculation that humans might obtain part of their biotin requirements from the intestinal flora in the colon. The question that has not been adequately answered is whether there is significant absorption of bacteria-produced biotin from the colon.

Infants

Children (1-13 years) Adolescents (14-18 years) Adults Pregnancy Lactation EAR

None reported RDA

None reported UL

None reported

5-6 jxg/day 8-20 /xg/day 25 jug/day 30 jag/day 30 jag/day 35 /Ag/day

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