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DRI Dietary Reference Intakes Calcium Vitamin D
of 50 percent of this population, and hence an EAR (rather than an AI). Moreover, as discussed in Chapter 2, peak calcium accretion with higher total calcium intakes is likely transitory and, thus, not consistent with DRI development.
The application of the factorial method using average bone calcium accretion allows an estimate of the calcium intake required to support bone accretion and net calcium retention, as shown in Table 5-2. The approach is described below, specifically for each life stage for children and adolescents.
Children 1 Through 3 Years of Age
The data are very limited for children 1 through 3 years of age given the challenges in studying young children. However, a report by Lynch et al. (2007) provides relevant data. Linear and non-linear modeling in this study suggested a target average calcium retention level of 142 mg/day, consistent with the growth needs of this life stage group. Through the factorial method, a calcium intake of 474 mg/day is estimated to meet this need (see Table 5-2). Given that these data are derived from mean estimates and are assumed to be normally distributed, the mean value is very likely the median value. An estimated EAR is, therefore, established as 500 mg of calcium per day, rounded from 474 mg/day.
An assumption specified by Lynch et al. (2007) is that an additional 30 percent calcium retention would meet the needs of 97.5 percent of this age group. This was calculated as 180 mg/day and is based on calcium absorptive efficiency for young children, and it is judged reasonable. This results in an estimated RDA for calcium of 700 mg/day calcium, with rounding.
Clearly, there are uncertainties when reliance is placed on a single study. The ability to study calcium requirements in a controlled study, however, does offer the ability to estimate an average requirement rather than an AI. The study is of high quality, and the reference values specified are in line with those specified for younger and older children.
Children 4 Through 8 Years of Age
The work of Abrams et al. (1999) and Ames et al. (1999) has indicated that, like that for younger children, an average calcium retention level of approximately 140 mg/day is consistent with the needs of bone accretion. However, there is evidence of a small increase during pre-puberty, yielding a calcium retention range of approximately 140 to 160 mg/day to allow for bone accretion across this age group of which a portion will be pre-pubertal. Using the factorial method (see Table 5-2) and from the non-linear dose–response relationship identified by the work of Ames