milk, then a net calcium retention will be achieved that is at least comparable to that of the human milk-fed infant. Based on an average intake from human milk of 210 mg (5.3 mmol)/day, intakes of 315 mg (7.9 mmol)/day from formula should be adequate for infants 0 through 6 months of age. For infants ages 7 through 12 months, based on an average intake from human milk of 130 mg (3.2 mmol)/day, 195 mg (4.8 mmol)/day should be obtained from formula. When added to the average intake of calcium (by formula-fed infants) from solid food of 140 mg (3.5 mmol)/day, an intake of 335 mg (8.3 mmol)/day is adequate for infants ages 7 through 12 months who are fed formula and solid foods.
It is difficult to accurately estimate the calcium intake needed for infants fed the various special formulas, including soy protein-based and protein hydrolysate formulas. However, based on the data of Rigo et al. (1995) and Fomon and Nelson (1993), an additional 20 percent above the 315 mg (7.9 mmol) calculated above should be sufficient to compensate for decreased bioavailabilty from those sources. This added amount is likely to result in a net calcium retention comparable to that of infants fed formula with higher calcium concentrations.
Hypocalcemia. Hypocalcemia is a relatively common neonatal problem (Salle et al., 1990). However, this condition requires special evaluation, which is beyond the scope of an evaluation of the AI for calcium for a healthy population of infants.
Balance Studies. Much of the available data from balance studies of young children, which were principally conducted prior to 1960, have been compiled and reviewed (Matkovic, 1991; Matkovic and Heaney, 1992). In 2- to 8-year-old children, mean calcium intakes (± SD) of 821 ± 63 mg (20.5 ± 1.5 mmol)/day led to calcium retentions of 174 ± 81 mg (4.3 ± 2.0 mmol)/day (about 21 percent of intake).
A recent study used stable isotopes to estimate calcium retention from milk in girls 5 to 12 years of age (Abrams and Stuff, 1994). Calcium intake based on 3-day dietary records was 907 ± 188 mg (22.7 ± 4.7 mmol)/day, urinary calcium excretion was 78 ± 48 mg (2.0 ± 1.2 mmol)/day, and mean absorption fraction was 28 ± 8 percent. Using estimated values for endogenous fecal calcium excretion of 1.4 ± 0.4 mg/kg/day (Abrams et al., 1991), their calculated