Several factors have been identified that affect the biotin requirement: the ingestion of large quantities of raw eggwhite, which contains a substance (avidin) that binds biotin; biotinidase deficiency (a genetic defect); the use of anticonvulsants that induce biotin catabolism in some individuals; and pregnancy. In the latter two conditions, the ratio of biotin metabolites to biotin in urine is increased (Mock and Dyken, 1997; Mock and Stadler, 1997; DM Mock et al., 1997b). Inherited biotinidase deficiency is particularly relevant to understanding biotin deficiency because the clinical manifestations appear to result largely from a secondary biotin deficiency in the presence of normal dietary intakes.
An Adequate Intake (AI) is used as the goal for intake by infants. The AI reflects the observed mean biotin intake of infants fed principally with human milk.
Ages 0 through 6 Months. In early and transitional human milk, the concentration of biotin metabolites is nearly twice the concentration of biotin in samples (DM Mock et al., 1997a). With postpartum maturation of milk production, the biotin concentration increases but the metabolites still account for approximately one-third of total biotin at 5 weeks postpartum. In mature human milk (greater than 21 days postpartum) the concentration of biotin varies substantially (Mock et al., 1992); it exceeds the concentration in serum by one to two orders of magnitude. This suggests that there is an active biotin transport system into milk. According to Hirano and coworkers (1992), estimates of the biotin content of milk are 3.8 ± 1.2 (standard deviation) µg/L as free biotin determined microbiologically and 5.2 ± 2.1 µg/L after acid hydrolysis—slightly higher than earlier estimates of 4.5 µg/L (Salmenpera et al., 1985) and 7 µg/L for total biotin from bioassays (Paul and Southgate, 1978). With greatest weight given to the recent results (Hirano et al., 1992), but with the value within the range of the two other studies (Paul and Southgate, 1978; Salmenpera et al., 1985), the biotin content of human milk was estimated to be 6 µg/L. The adequate intake for biotin for