Calcium absorption for this age group ranges somewhat above and below 60 percent depending upon the total amount of calcium consumed. For development of the AI, a 60 percent calcium absorption rate was assumed.
The usual accretion rate for calcium in infants can be estimated using the approximation of 100 mg/day overall during the first year of life, with the recognition that the available literature contains reports of varying rates above and below that level.
Using the estimates described above for the calcium content of breast milk and the amount of milk consumed per day, the AI for calcium for infants 0 to 6 months of age is 200 mg/day, a value reflective of the calcium provided to exclusively breast-fed infants. The expected net retention of calcium from human milk assuming 60 percent absorption would be 120 mg/day, which is in excess of the values predicted from calcium accretion based on cadaver and metacarpal analysis. An AI of 200 mg/day is expected, therefore, to result in retention of sufficient amounts of calcium to meet growth needs.
Further, for infants in the first 4 months of life, balance studies suggest that 40 to 70 percent of the daily calcium intake is retained by the human milk-fed infant (Widdowson, 1965; Fomon and Nelson, 1993). In balance studies using human milk–fed infants, the mean calcium intake was 327 mg/day, and calcium retention was 172 mg/day on average (Fomon and Nelson, 1993). If infants consume calcium at the AI daily, they would achieve similar or greater calcium retention even if the efficiency of absorption was at the lower observed value of 30 percent. Thus, the AI should meet most infants’ needs.
The AI established here of 200 mg/day is similar to the AI of 210 mg/day derived by the 1997 report (IOM, 1997). The difference is extremely small—only 10 mg/day—and likely within measurement error; however, the new AI reflects the current best estimate for calcium levels obtained exclusively from human milk
Estimation of the AI for infants 6 to 12 months of age takes into account the additional intake of calcium from food. From 6 to 12 months of age, the intake of solid foods becomes more significant, and calcium intakes may increase substantially from these sources. Only extremely limited data are available for typical calcium intakes from foods by older milk-fed infants, and mean calcium intake from solid foods has been approxi-