Data are not sufficient to establish an EAR for infants less than 1 year of age, and therefore an AI has been developed. Unlike the case for calcium, the content of human milk does not shed light on the vitamin D requirements of infants, as breast milk is not a meaningful source of vitamin D.

The AI for the 0 to 6 months and 6 to 12 months life stage groups is set at 400 IU of vitamin D per day. There are very limited data beyond the conclusion that maintaining serum 25OHD concentrations in this life stage group above 30 nmol/L, and more likely closer to 50 nmol/L, appears to cover adequately the needs of the majority of the infants and support normal bone accretion. There are no data to suggest that older infants would benefit from higher intakes.

Intakes in the range of 400 IU/day appear consistent with maintenance of the desirable serum 25OHD concentrations. There are no reports of a clinical deficiency in infants receiving 400 IU of vitamin D per day, and an intake of 400 IU/day appears to maintain a serum 25OHD level generally above 50 nmol/L in infants (Greer et al., 1982; Rothberg et al., 1982; Ala-Houhala, 1985; Ala-Houhala et al., 1988; Greer and Marshall, 1989; Hollis and Wagner, 2004). There are differences in the volume of milk or formula intake during this 12-month period, with newborns taking in less than older infants. The AI of 400 IU/day, therefore, represents an overall intake for the first year of life, and may vary across the life stages; it also assumes early introduction of a supplement for breast-fed babies. In the case of exclusive formula feeding, there is an assumption of a gradual increase in intake to 800 to 1,000 mL/day during infancy, which for most standard formulas provides about 400 IU/day. Note is made of the case reports concerning the development of rickets among dark-skinned infants who are exclusively breast-fed and not provided a vitamin D supplement (see Chapter 8).

For these life stage groups, ensuring normal, healthy bone accretion is central to the DRI values. The requirement distribution developed using serum 25OHD concentrations and the intakes estimated to achieve such concentrations are the basis for the reference values.