no-observed-adverse-effect level (NOAEL) and lowest-observed-adverse-effect level (LOAEL) are determined based on these factors if data are available to do so. Next, an uncertainty factor is applied to the NOAEL or LOAEL. The uncertainty factor is based on expert judgment of the uncertainties of extrapolating from the observed data to the general population. Dividing the NOAEL or LOAEL by the uncertainty factor results in the UL.

The third step is an assessment of the range and distribution of intake or exposure of the nutrient or food component in the general population. If the adverse effect appears to be associated with intake from dietary supplements only, then the UL is for supplements only. It is clearly indicated whether the UL is for total intake, intake from supplements only, or intake from fortified foods and supplements.

The last step is a characterization of the risk. The range of reported intakes of the nutrient is compared with the UL. If a large fraction of the general population is consuming chronic intakes above the UL, this could be a potential at-risk group. The UL does not include policy decisions, but the rationale suggests risk management guidelines for determining the significance of the risk to a population consuming a nutrient at levels above the UL.


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CDER (Center for Drug Evaluation and Research). 2001. Milestone Status of OTC Drug Review Documents as of March 1, 2001. Online. Food and Drug Administration. Available at Accessed March 28, 2002.

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