Longitudinal changes in dietary zinc requirements for infants at different levels of net absorption were estimated using a factorial approach. Apart from variations in net absorption, the zinc needed for new lean body mass is the major determinant of requirements. As growth velocity declines progressively, estimated zinc requirements for growth and for replacement of urine and sweat losses decrease from a high for male infants of 780 micrograms/day at 1 mo to 480 micrograms/day in the 5th mo and then remain quite constant through the 1st yr. Calculated percentage absorption of zinc from human milk necessary to meet estimated requirements increases with duration of lactation. For infants of mothers whose zinc intake approximated 25 mg/day the calculated percentage absorption remained within plausible limits. It is suggested that the progressive decrease in milk zinc concentrations provides a mechanism for conserving maternal zinc while meeting infant needs.
PIP: This study aims to estimate longitudinal changes in dietary zinc requirements of infants with a factorial approach, and to use these estimates to evaluate the adequacy of calculated zinc intakes of the fully breast fed infant. Rates calculated are growth velocity, zinc concentration of lean body mass, zinco excretion is urine and sweat, milk zinc concentrations and milk volume. Apart from variations in net absorption, the zinc needed for new lean body mass is the major determinant of infant zinc requirements. Hence these requirements are relatively high in the very young infant and decrease with increasing age of the infant. As growth velocity declines progressively, estimated zinc requirements for growth and for replacement of urine and sweat losses decrease from a high for male infants of 780 ug/day at 1 month to 480 ug/day in the 5th month and then remain quite constant through the 1st year. Calculated % absorption of zinc from human milk necessary to meet estimated requirements increases with duration of lactation. For infants of mothers whose zinc intake approximated 25mg/day the calculated % absorption remained within plausible limits. It is suggested that the progressive decrease in milk zinc concentrations provides a mechanism for conserving material zinc while meeting infant needs.