of estrogen, smoking, or sedentary lifestyle. Thus not all bone loss can be prevented by additional dietary calcium.

The balance studies used in this report were reviewed rigorously to meet specific criteria which included the following: subjects consumed a wide range of calcium intakes since variability in retention increases at higher intakes; the balance studies were initiated at least 7 days after starting the diet in order for subjects to approach a steady state as observed by Dawson-Hughes et al. (1988); and, where possible, the adult balance studies included were only for subjects who were consuming their usual calcium intakes unless otherwise indicated. By selecting studies conducted on such subjects, it obviates the concern about whether the bone remodeling transient might introduce bias in the calcium retentions observed. Such selection was not possible in studies in children where they have been randomized to one of two calcium intakes. However, in children the impact of the remodeling transient related to changing intake is overshadowed by their rapid and constantly changing rates of calcium accretion (for example, their modeling and remodeling rates are not in steady state even without an intake change).

The non-linear regression model describing the relationship between calcium intake and retention was solved to obtain a predicted calcium intake for a predetermined desirable calcium retention1 which was specific for each age group. The basis of the value

1  

The Panel on Calcium and Related Nutrients proposed use of a recently described statistical model (Jackman et al., 1997) to estimate an intake necessary to support maximal calcium retention and from which to derive an EAR. In the original paper by Jackman et al. (1997), an estimate was made of the lowest level of calcium intake that was statistically indistinguishable from 100 percent maximal retention in some individuals. However, the Standing Committee on the Scientific Evaluation of Dietary Reference Intakes (DRI Committee) adopted a different interpretation of the data for the purpose of establishing an AI. The approach adopted is described in the prepublication version of this final report. The DRI Committee was subsequently advised that there were both statistical and biological concerns with the application of the percent maximal retention model (see Appendix E). After seeking input from the Panel on Calcium and Related Nutrients, the DRI Committee has chosen, for the final print of the report, to retain the statistical model described by Jackman et al. (1997), but to apply it to determine, from the same calcium balance data as was used in the prepublication report, an estimate of the calcium intake that is sufficient to achieve a defined, desirable level of calcium retention specific to the age groups considered. The mathematical modeling and basis of the equations were kindly provided for the report by Dr. George McCabe and Dr. Connie Weaver of Purdue University and are described in detail in Appendix E.



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