ing effects after subchronic exposures, when data are lacking on chronic exposures.

Selection of a UF for Calcium, Phosphorus, Magnesium, Vitamin D, and Fluoride

The selection of a UF of approximately 1.0 for fluoride and magnesium is primarily based on the very mild (and in the case of magnesium, reversible) nature of the adverse effects observed. A slightly larger UF (1.2) was selected for vitamin D intake in adults and other life stage groups except infants as the short duration of the study used (Narang et al., 1984) and the small sample size supports the selection of a slightly larger UF. For vitamin D in infants, a larger UF (1.8) was selected due to the insensitivity of the critical endpoint, the small sample sizes of the studies, and limited data about the sensitivity at the tails of the distribution. A UF of 2 was selected for calcium to account for the potential increased susceptibility to high calcium intake by individuals who form renal stones and the potential to increase the risk of mineral depletion in vulnerable populations due to calcium-mineral interactions. A UF of 2.5 was selected for phosphorus due to the lack of information on potential adverse effects in the range between normal phosphorus levels and levels associated with ectopic mineralization. The selection of a UF for phosphorus that is larger than those for the other nutrients evaluated is also due to the relative lack of human data describing adverse effects of excess phosphorus intake.

Derivation of a UL

The UL is derived by dividing the NOAEL (or LOAEL) by all the relevant UFs. The derivation of a UL involves the use of scientific judgment to select the appropriate NOAEL (or LOAEL) and UF. The framework or model outlined in this chapter for characterizing the potential risk (for example, scientific judgment used in deriving a UL from a NOAEL [or LOAEL]) is provided from a nutritional risk assessment perspective. This perspective is consistent with that of classical risk assessment in that it requires explicit consideration and discussion of all choices made, both regarding the data used and the uncertainties accounted for.

Characterization of the Estimate and Special Considerations

ULs are derived for various life stage groups utilizing relevant



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