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Trace Elements

Previous editions of the RDAs in the United States (NRC, 1980, 1989) established a category of estimated safe and adequate daily dietary intakes (ESADDI) for essential nutrients with databases that were insufficient for developing an RDA, but where evidence of potentially toxic intakes was known. The values for ESADDI typically were ranges of intakes. The DRI process has taken a different approach. If the data required to establish intake recommendations (either an EAR and RDA, or an AI) were not available, as is the case for arsenic, boron, nickel, silicon, and vanadium in this report, no requirement is set. However, the database was adequate to establish ULs for boron, nickel, and vanadium. Therefore, for these nutrients an upper limit has been set, but not a lower limit. Accordingly, when intake data are available, users can estimate the proportion of the population that may be at risk from excessive intakes of these elements.


The Dietary Reference Intakes (DRIs) may be used to assess nutrient intakes as well as for planning nutrient intakes. Box 14-1 summarizes the appropriate uses of the DRIs for individuals and groups.

For the nutrients presented in this report, only iron requires the use of the full probability approach to estimate the prevalence of inadequacy due to skewedness of the requirement distributions. Guidance is provided for adjustments to the iron requirement for several special situations, including onset of menarche before age 14 years in girls, onset of the growth spurt in adolescent males and females, use of oral contraceptives, athletes, vegetarians, and frequent blood donors.

Adjustments to zinc requirements are also recommended on the basis of the impact of the zinc:phytate ratio on bioavailability of zinc.

Examples are provided of ways to determine the appropriate adjustments to estimates of the usual intake of vitamin A considering the change in the vitamin A activity of provitamin A carotenoids.

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