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Thus, caution is warranted; food should be the source of intake by infants.

ULs for niacin, vitamin B12, and choline in children and adolescents were determined by extrapolating from the UL for adults based on body weight differences by using the formula

ULchild = (ULadult) (Weightchild/Weightadult)0.75.

See Chapter 2 for related information about extrapolation.

With the use of data from Table 1-2 (Chapter 1), the reference weight for males ages 19 through 30 years was used for adults and the reference weights for female children and adolescents were used in the formula above to obtain the UL for each age group. The use of these reference weights yields a conservative UL to protect the sensitive individuals in each age group.

The derivation of a UL involves the use of scientific judgment to select the appropriate NOAEL (or LOAEL) and UF. The risk assessment requires explicit consideration and discussion of all choices made, both regarding the data used and the uncertainties accounted for. These considerations are discussed in the chapters on nutrients. Because of lack of suitable data, ULs could not be set for infants or for thiamin, riboflavin, vitamin B12, pantothenic acid, or biotin.

Characterization of the Estimate and Special Considerations

ULs are derived for various life stage groups by using relevant databases, NOAELs and LOAELs, and UFs. Where no data exist for NOAELs or LOAELs for the group under consideration, extrapolations from data in other age groups and/or animal data are made on the basis of known differences in body size, physiology, metabolism, absorption, and excretion of the nutrient.

If the data review reveals the existence of subpopulations having distinct and exceptional sensitivities to a nutrient’s toxicity, these subpopulations are considered under the heading “Special Considerations.”

REFERENCES

Dourson ML, Stara JF. 1983. Regulatory history and experimental support of uncertainty (safety) factors. Regal Toxicol Pharmacol 3:224–238.


EPA (U.S. Environmental Protection Agency). 1996. Proposed guidelines for carcinogen risk assessment; Notice. Fed Regist 61:17960–18011.



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