Dietary Reference Intakes for Calcium, Phosphorus, Magnesium, Vitamin D, and Fluoride (1997) / Chapter Skim
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3 A Model for the Development of Tolerable Upper Intake Levels
3 A Model for the Development of Tolerable Upper Intake Levels
Pages 51-70
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From page 51... ...
that may be especially vulnerable to one or more adverse effects. The term Tolerable Upper Intake Level is clefineci as the maximum ~1
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From page 52... ...
(A fuller discussion of this problem is set forth in the section on "Risk Assessment and Food Safety".) Scientific information regarding various adverse effects and their relationships to intake levels varies greatly among nutrients, depending on the nature, comprehensiveness, and quality of available data and the uncertainties associated with the unavoidable problem of extrapolating from the circumstances under which data are developed (for example, in the laboratory or clinic)
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From page 53... ...
Risk management clecisions clepenci on the results of risk assessments but may involve aciclitional considerations, such as the public health significance of the risk, the technical feasibility of achieving various degrees of risk control, and the economic and social costs of this control. Because
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From page 54... ...
those associated with any inferences that are required when directly applicable data are not available (NRC, 1994~. Data uncertainties arise in the evaluation of information obtained from the epidemiology and toxicology studies and investigations of nutrient intake levels that are the basis for risk assessments.
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· Step 3. Exposure assessment evaluates the distribution of usual total tinily nutrient intakes among members of a healthy population.
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The adverse effects that may be caused by a nutrient almost certainly occur only when the threshold close is exceecleci. The critical issues concern the methods used to identify the approximate threshold of toxicity for a large and diverse human population.
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It is cleriveci by application of the hazard identification and close-response evaluation steps (Steps 1 and 2) of the risk assessment model.
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From page 58... ...
Moreover, ciata on nutrient toxicity are often available from studies in human populations and are therefore not usually subject to the degree of uncertainty associateci with the types of ciata available on nonessential chemicals. In addition, there is no evidence to suggest that nutrients consumeci at the RDA or AI and as part of unfortified cliets present a risk of adverse effects to the healthy population.
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From page 59... ...
Consideration of Variability in Sensitivity The risk assessment model outlined in this chapter is consistent with classical risk assessment approaches in that it must consider variability in the sensitivity of inclivicluals to adverse effects. A cliscussion of how variability is dealt with in the context of nutritional risk assessment is provicleci here.
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From page 60... ...
Modulating components include: other clietary components; concentration and chemical form of the nutrient in food, water, nutrient supplements, and over-the-counter pharmaceutical preparations; the nutritional, physiological, and disease state of the incliviclual; and excretory losses. Because of the considerable variability in nutrient bioavailability in humans, bioavailability ciata for specific nutrients must
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From page 61... ...
Nutrient Interactions It is well established that certain nutrients interact with each other to alter bioavailabilit,Y. For example, clietar,y interactions can affect the chemical forms of elements at the site of absorption through liganci binding or changes in the valence state of an element (Mertz et al., 1994~.
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From page 62... ...
Although data from controlled studies in humans are the basis for establishing nutritional requirements, the number of controlled human toxicity studies conclucteci in a clinical setting are, for ethical reasons, very limited and are useful for identifying only very mild and completely reversible adverse effects. Nevertheless, the available human ciata provide the most relevant kind of information for hazard identification and, when they are of sufficient quality and extent, are given greatest weight.
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From page 63... ...
In the hazard identification step, all human, animal, and in vitro published evidence aciciressing the likelihood of a nutrient eliciting an adverse effect in humans is examined. Decisions regarding which observed effects are "adverse" are baseci on scientific judgments.
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The risk assessment process recognizes that there may be individuals within any life stage group that are more biologically sensitive than others. The ULs cleriveci for nutrients in this document are baseci on protecting the most sensitive members of a healthy population.
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From page 65... ...
, and assessment of uncertainty. Data Selection The ciata evaluation process results in the selection of the most appropriate or critical ciata setts)
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From page 66... ...
Furthermore, the critical ciata set should document the intake that clods not produce adverse effects, the NOAEL, as well as the intake producing toxicity. Identification of NOAET (or TOWEL)
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From page 67... ...
While the UFs selected for nonessential chemical agents are usually multiples of 10, the data on nutrient toxicity may not be subject to the same uncertainties as with nonessential chemical agents since data are generally available regarding intakes of human populations. The UFs for nutrients are typically less than 10 depending on the quality and nature of the data and the adverse effects involved.
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From page 68... ...
The selection of a UF for phosphorus that is larger than those for the other nutrients evaluated is also clue to the relative lack of human ciata describing adverse effects of excess phosphorus intake. Derivation of a UT The UL is derived by dividing the NOAEL (or LOAEL)
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From page 69... ...
Risk: Within the context of nutrient toxicity, the probability or likelihooci that some adverse effect will result from a specified excess intake of a nutrient. Risk Assessment: An organized framework for evaluating scientific information, which has as its objective a characterization of the nature and likelihood of harm resulting from excess human exposure to an environmental agent (in this case, a clietary nutrient)
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From page 70... ...
In aciclition to risk assessment results, risk management considers such issues as the public health significance of the risk, the technical feasibility of achieving various degrees of risk control, and the economic and social costs of this control. Tolerable Upper Intake Level (UL)
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