associated with positive effects on bone mineral accretion, especially during the pre-pubertal stage (Table 4-2). In the Lloyd et al. (1993) study, girls with a mean age of 11.9 years were supplemented (total daily intake of 1,370 ± 303 mg [34.2 ± 7.6 mmol]) and compared with a placebo group (total daily intake 935 ± 258 mg [23.4 ± 6.4 mmol]). After 18 months of supplementation, the girls had greater increases in lumbar spine BMD (18.7 versus 15.8 percent), lumbar spine BMC (39.4 versus 34.7 percent), and total body BMD (9.6 versus 8.3 percent). In the Chan et al. (1995) study, the girls (mean age 11 years) supplemented for 12 months (total daily intake 1,437 ± 366 mg [35.9 ± 9.2 mmol]) had significantly greater increases in lumbar spine BMD (22.8 ± 6.9 versus 12.9 ± 8.3 percent) and total body BMC (14.2 ± 7.0 versus 7.6 ± 6.0 percent) than control subjects (total daily intake 728 ± 321 mg [18.2 ± 8.0 mmol]). In a third study (Johnston et al., 1992), identical twins, aged 6 to 14 years, were given a supplement (total daily intake approximately 1,600 mg [40 mmol]) or a placebo (daily intake 900 mg [22.5 mmol]). When examined by pubertal status, the prepubertal twins (22 pairs) had a greater bone response to calcium supplementation than did the pubertal twins (23 pairs). The pubertal subjects in this study showed no significant effect of supplementation, unlike the pubertal girls in both the Lloyd et al. (1993) and Chan et al. (1995) studies.

Mounting evidence from randomized clinical trials suggests that the bone mass gained during childhood and adolescence through calcium or milk supplementation is not retained postintervention (Fehily et al., 1992; Lee et al., 1996; Slemenda et al., 1997). Upon cessation of the intervention, the component of calcium's effect due to reduction of the remodeling space disappears, as the space expands again. Further research is required to determine the long-term effects of higher calcium intakes during adolescence and the specific effect of calcium intake on bone modeling and achievement of genetically programmed peak bone mass.

Factorial Approach. For children ages 9 through 18 a more traditional factorial approach for estimating calcium requirements is to sum calcium needs for growth (accretion) plus calcium losses (urine, feces, and sweat) and adjust for absorption. Using this method, estimates for calcium requirements for adolescent girls and boys are 1,276 and 1,505 mg (31.9 and 37.6 mmol)/day, respectively (Table 4-3). Calcium accretion estimates, based on whole body bone mineral mass measurements by DXA, were obtained from a 4-year prospective study in 228 children aged 9.5 to 19.5 years (Mar-



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