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4 A Model for the Development of Tolerable Upper Intake Levels for Nutrients
Pages 73-94

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From page 73...
... Many inclivicluals are self-meclicating with nutrients for perceived prophylactic or curative purposes. It is beyond the scope of the model at this time to aciciress whether there are benefits of higher nutrient intakes that may offset the risk of adverse effects.
From page 74...
... However, it is possible to develop intake levels that are unlikely to pose risk of adverse health effects for most members of the general population, including sensitive inclivicluals. For some nutrients or food components, these intake levels may however pose a risk for subpopulations with extreme or distinct vulnerabilities.
From page 75...
... Scientific information regarding various adverse effects and their relationships to intake levels varies greatly among nutrients and depends on the nature, comprehensiveness, and quality of available data. The uncertainties associated with the unavoidable problem of extrapolating from the circumstances under which data are developed (e.g., the laboratory or clinic)
From page 76...
... Risk assessment is subject to two types of scientific uncertainties: those related to ciata and those associated with inferences that are required when directly applicable ciata are not available (NRC, 1994~. Data uncertainties arise cluring the evaluation of information obtained from the epiclemiological and toxicological studies of nutrient intake levels that are the basis for risk assessments.
From page 77...
... · Derivation of Tolerable Upper Intake Level (UL) Intake Assessment Evaluation of the range and the distribution of human intakes of the nutrient or the food component Risk Characterization · Estimation of the fraction of the population, if any, with intakes greater than the UL · Evaluation of the magnitude with which these excess intakes exceed the UL FIGURE 4-1 Risk assessment model for nutrient toxicity.
From page 78...
... · Step 3. Intake assessment evaluates the distribution of usual total daily nutrient intakes among members of the general population.
From page 79...
... ~ that account for interspecies and intraspecies differences in response to the hazardous effects of substances and for other uncertainties (WHO, 1987~. Uncertainty factors are used to make inferences about the threshold close of substances for members of a large and diverse human population from ciata on adverse effects obtained from epiclemiological or experimental stuciies.
From page 80...
... to the derivation of Tolerable Upper Intake Levels (ULs) for nutrients.
From page 81...
... Such elevations alone may pose risks of adverse effects; imbalances among the vitamins or other nutrients may also be possible. These reasons and those cliscusseci previously support the neeci to include the form and pattern of consumption in the assessment of risk from high nutrient or food component intake.
From page 82...
... Physiological changes and common conditions associated with growth and maturation that occur cluring an incliviclual's life span may influence sensitivity to nutrient toxicity. For example, sensitivity increases with declines in lean body mass and with cleclines in renal and liver function that occur with aging; sensitivity changes in direct relation to intestinal absorption or intestinal synthesis of nutrients; in the newborn infant, sensitivity is also increased because of rapid brain growth and limited ability to secrete or biotransform toxicants; and sensitivity increases with decreases in the rate of metabolism of nutrients.
From page 83...
... Some nutrients may be less readily absorbed when they are part of a meal than when taken separately. Supplemental forms of some nutrients may require special consideration if they have higher bioavailability and therefore may present a greater risk of producing adverse effects than equivalent amounts from the natural form found in food.
From page 84...
... Observational studies that focus on welldefined populations with clear exposures to a range of nutrient intake levels are useful for establishing a relationship between exposure and effect. Observational data in the form of case reports or anecdotal evidence are used for developing hypotheses that can lead to knowledge of causal associations.
From page 85...
... Evidence of Adverse Effects in Humans The hazard identification step involves the examination of human, animal, and in vitro published evidence aciciressing the likelihooci of a nutrient or food component eliciting an adverse effect in humans. Decisions regarding which observed effects are adverse are baseci on scientific judgments.
From page 86...
... to clietary intakes by human populations. Pharmacokinetic and Metabolic Data When available, ciata regarding the rates of nutrient absorption, distribution, metabolism, and excretion may be important in clerivation of Tolerable Upper Intake Levels (ULs)
From page 87...
... Identification of Distinct and High;ly Sensitive Subpopu;tations The ULs are baseci on protecting the most sensitive members of the general population from adverse effects of high nutrient or food component intake. Some highly sensitive subpopulations have responses (in terms of incidence, severity, or both)
From page 88...
... Data Selection and Identification of Cr~tica;t Endpoints The ciata evaluation process results in the selection of the most appropriate or critical ciata sets for deriving the UL. Selecting the critical ciata set includes the following considerations: · Human ciata, when acloquate to evaluate adverse effects, are preferable to animal ciata, although the latter may provide useful supportive information.
From page 89...
... The Tolerable Upper Intake Level (UL) is the highest level of daily nutrient intake that is likely to pose no risk of adverse health effects for almost all individuals in the general population.
From page 90...
... Because ciata are generally available regarding intakes of nutrients and food components by human populations, the ciata on nutrient toxicity may not be subject to the same uncertainties as ciata on nonessential chemical agents, resulting in UFs for nutrients and food components typically less than the factors of 10 often applied to nonessential toxic substances. The UFs are lower with higher quality ciata and when the adverse effects are extremely mild and reversible.
From page 91...
... · Subchronic NOAEL to predict chronic NOAEL. When ciata are lacking on chronic exposures, scientific judgment is necessary to determine whether chronic exposure is likely to leaci to adverse effects at lower intakes than those producing effects after subchronic exposures (exposures of shorter cluration)
From page 92...
... RISK CHARACTERIZATION As clescribeci earlier, the question of whether nutrient intakes create a risk of adverse effects requires a comparison of the range of nutrient intakes (food, supplements, and other sources or supplements alone, clepencling upon the basis for the Tolerable Unner Level Intake FULL ~ with the UL. Figure 4-3 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.
From page 93...
... the fraction of the population consistently consuming the nutrient at intake levels in excess of the UL; 2. the seriousness of the adverse effects associated with the nutrient; 3.
From page 94...
... Twenty-sixth report of the Joint FAD/WHO Expert Committee on Food Additives. WHO Technical Report Series No.


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