Because estimates of the biotin requirement for infants currently are
based on the biotin concentration in human milk, we sought to determin
e whether inactive boitin metabolites are present. Samples were collec
ted for 7 weeks post partum from 15 healthy women. Biotin and the inac
tive metabolites bisnorbiotin and biotin sulfoxide were measured by me
ans of a high-performance liquid chromatography avidin-binding assay.
At 8 days post partum the proportion of biotin was 44%, bisnorbiotin 4
8%, and biotin sulfoxide 8%. Although biotin content increased post pa
rtum (p < 0.003), the metabolites remained an important portion of the
total providing evidence that accurate measurement of biotin in human
milk requires an assay that is specific for biotin.