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In order to match the zinc intake of the infant in early weeks (Figure 12-3), the AI is set at 2.0 mg/day (2.5 mg/L × 0.78 L/day). This amount appears to be generous at ages 4 to 6 months when evaluated by zinc intake from human milk at this age, and human milk has been shown to result in weight gain and body lengths similar to those of infants provided complementary foods at 4 to 6 months (Dewey et al., 1999). A positive association between zinc content of human milk at 5 months and changes in the weight-forage Z scores for the 5- to 7-month interval have, however, been documented (Krebs et al., 1994). There is also some evidence, however, that growth-limiting zinc deficiency can occur in infants principally fed human milk after the age of 4 months (Walravens et al., 1992).

Factorial estimates of requirements (i.e., 2.1 mg/day at 1 month and 1.54 mg/day at 5 months) are consistent with this AI for infants ages 0 through 6 months. These factorial estimates are based on measurements of zinc intake of infants fed human milk, fractional absorption, and endogenous losses (Krebs et al., 1996). Integumental and urine losses are from published calculations (Krebs and Hambidge, 1986). Also consistent with this AI is an earlier report that physical growth of male infants fed a zinc-fortified cow milk formula (5.8 mg/L) was greater than that of infants receiving the same formula but with a zinc concentration of 1.8 mg/L, which provided about 1.4 mg/day of zinc (Walravens and Hambidge, 1976).

Zinc AI Summary, Ages 0 through 6 Months

AI for Infants

0–6 months

2.0 mg/day of zinc

Special Considerations

The zinc concentration in cow milk ranges from 3 to 5 mg/L (Lonnerdal et al., 1981) which is greater than the average concentration in human milk (Table 12-1). Singh and coworkers (1989) reported that approximately 32 percent of zinc in cow milk is bound to casein and the majority of the remaining zinc (63 percent) is bound to colloidal calcium phosphate. The absorption of zinc from human milk is higher than from cow milk-based infant formula and cow milk (Lonnerdal et al., 1988; Sandstrom et al., 1983). The zinc bioavailability from soy formulas is significantly lower than from milk-based formulas (Lonnerdal et al., 1988; Sandstrom et al., 1983).

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