Because there are not sufficient data that reliably reflect response to dietary riboflavin intake in infants, an Adequate Intake (AI) is used as the goal for intake by infants. In this case, the AI reflects the observed mean riboflavin intake of infants fed principally with human milk.
The riboflavin content of human milk used for calculations in this report is based on milk from healthy, well-nourished mothers who are not taking supplements. In the first few weeks postpartum, the riboflavin content of milk tends to increase with the use of riboflavin supplements (Nail et al., 1980). However, no difference in riboflavin content of human milk was found between supplemented and unsupplemented well-nourished mothers at 6 months postpartum (Thomas et al., 1980). Previously, estimates of the riboflavin content of human milk from well-nourished, unsupplemented mothers included 0.37 ± 0.13 (standard deviation) mg/L at 5 to 7 days postpartum, 0.49 ± 0.12 mg/L at 43 to 45 days postpartum, 0.24 ± 0.35 mg/L at 6 months postpartum (Thomas et al., 1980), and 0.35 ± 0.02 mg/L after 3 weeks postpartum (Committee on Nutrition, 1985).
More recent studies (Roughead and McCormick, 1990a, b) in five subjects showed that riboflavin in milk may have been previously underestimated as a result of a lack of detection of flavin-adenine dinucleotide (FAD), which by weight is 48 percent riboflavin (and accounts for 41 percent of total flavin in milk), by fluorescent measurement techniques. However, the antivitaminic potential of certain metabolites in milk, such as the 2'-hydroxyethylflavin, could suppress riboflavin efficiency by competition for cellular uptake (Aw et al., 1983) and utilization (McCormick, 1962). The net consequence is that the riboflavin equivalence of milk, either from humans or cows, may be somewhat higher than earlier estimates based on uncorrected fluorescence measurements. On the basis of this and studies of microbiologically determined riboflavin in human milk (WHO, 1965), a riboflavin concentration of 0.35 mg/L will be used for human milk consumed by infants younger than 6 months (see Box 5-1).