There are two general conditions under which ULs are not established. In some cases the lack of sufficient evidence regarding a nutrient’s capacity to cause adverse effects prohibits the application of the UL model. In other cases, the evidence is available but meeting the UL derived from such evidence will necessarily result in the introduction of undesirable health effects because of the required adjustments in dietary patterns.
The scientific evidence relating to adverse effects of nutrient excess varies greatly among nutrients. The type of data and evidence of causation used to derive ULs have been described in the earlier sections of this chapter, but such data and evidence are simply unavailable for some nutrients. In some cases, some data relating to adverse effects may be available but are of such uncertain relevance to human health that their use in deriving ULs is scientifically insupportable. In every instance in which ULs are not derived because of lack of adequate evidence, the specific limitations in the database are described.
To assess the risk of adverse effects, information on the range of nutrient intakes in the general population is required. As noted earlier, in cases where the Tolerable Upper Intake Level pertains only to supplement use and does not pertain to usual food intakes of the nutrient, the assessment is directed at supplement intakes only.
As described earlier, the question of whether nutrient intakes create a risk of toxicity requires a comparison of the range of nutrient intakes (food, supplements, and other sources or supplements alone, depending on the basis for the Tolerable Upper Intake Level [UL]) with the UL.
Figure 3-4 illustrates a distribution of chronic nutrient intakes in a population; the fraction of the population experiencing chronic intakes above the UL represents the potential at-risk group. A policy decision is needed to determine whether efforts should be made