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Dietary Reference Intakes for Vitamin A, Vitamin K, Arsenic, Boron, Chromium, Copper, Iodine, Iron, Manganese, Molybdenum, Nickel, Silicon, Vanadium, and Zinc
using a consistent basic method. The method relies on at least four assumptions:
Maintenance needs for vitamin A, chromium, copper, iodine, and molybdenum, expressed with respect to metabolic body weight ([kilogram of body weight]0.75), are the same for adults and children. Scaling requirements to the 0.75 power of body mass adjusts for metabolic differences demonstrated to be related to body weight, as described by Kleiber (1947) and explored further by West et al. (1997). By this scaling, a child weighing 22 kg would require 42 percent of what an adult weighing 70 kg would require—a higher percentage than that represented by actual weight. If there is a lack of evidence demonstrating an association between metabolic rate and nutrient requirement, needs are estimated directly proportional to total body weight.
The EAR for adults is an estimate of maintenance needs.
The percentage of extra vitamin A, chromium, copper, and molybdenum needed for growth is similar to the percentage of extra protein needed for growth.
On average, total needs do not differ substantially for males and females until age 14, when reference weights differ.
The formula for the extrapolation is
EARchild = EARadult × F,
where F = (Weightchild/Weightadult)0.75 × (1 + growth factor). Reference weights from Table 1-1 are used. If the EAR differs for men and women, the reference weight used for adults differs in the equation by gender; otherwise, the average for men and women is used. The approximate proportional increase in protein requirements for growth (FAO/WHO/UNA, 1985) is used as an estimate of the growth factor as shown in Table 2-1. If only an AI has been set for adults, it is substituted for the EAR in the above formula, and an AI is calculated; no RDA will be set.
Setting the RDA for Children
To account for variability in requirements because of growth rates and other factors, a 10 percent coefficient of variation (CV) for the requirement is assumed for children just as for adults unless data are available to support another value, as described in Chapter 1.