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Calcium retention levels Total body calcium at birth in healthy, full-term infants is approximately 30 g (Givens and Macy, 1933; Widdowson et al., 1951). Based on bone mineral accretion derived as a function of change in body weight, total body calcium increases to approximately 80 g by 1 year of age (Leitch and Aitken, 1959). This suggests an average accretion rate of approximately 140 mg calcium per day during the first year of life. This greatly exceeds the earlier accretion rate estimates, derived from cadaveric sources, of approximately 30 to 35 mg/day and 50 to 55 mg/day for infants through 4 months of age and 4 through 12 months of age, respectively (Fomon and Nelson, 1993; Koo and Tsang, 1997). Yet another mean accretion rate of approximately 80 mg/day during the first year of life has been derived using metacarpal morphometry data (Garn, 1972; Weaver, 1994). Resolution of these different values for usual accretion rate is not currently possible, but assessment of these data and the balance data suggests that a mean accretion rate of about 100 mg/day overall during the first year of life may serve as a reasonable approximation for primarily breast-fed infants (Abrams, 2010).

Information about bone accretion in young children is limited given the impracticalities associated with studies of young subjects. Lynch et al. (2007), using an isotope-based method, evaluated the relationship between calcium intake and balance in healthy children 1 to 4 years of age. They reported mean calcium retention of 161 mg/day with a mean calcium intake of 551 mg/day, reflecting a positive calcium balance. Linear and non-linear modeling indicated that calcium intakes of 470 mg/day yielded a calcium retention of 140 mg/day, consistent with the growth needs of this population (Lynch et al., 2007).

For slightly older children in the 7- to 8-year age range, the work by Abrams et al. (1999) has also demonstrated that the average calcium accretion rate is 140 mg/day5 calcium. A small increase is seen in late pre-puberty (Leitch and Aitken, 1959; Ellis et al., 1996), yielding a bone calcium accretion rate ranging from 140 to 160 mg/day across this age group, within which a small percentage will be pre-pubertal. Based on modeling, a curvilinear dose–response relationship between calcium intake and retention was made evident as shown in Figure 4-8.

A recent publication from Wu et al. (2010) that focused on Chinese American boys and girls 11 to 15 years of age reported calcium retention to be 1,100 mg/day in boys and 970 mg/day in girls, but these estimates were based on intakes to achieve maximal calcium retention as opposed to average calcium retention, the value needed to determine an EAR. A recent study of white children in Canada (Vatanparast et al., 2010) has provided bone calcium accretion levels for children and adolescents between the

5

The 140 mg/day value is a modeled value as described in the study (Abrams et al., 1999).



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