. "3 A Model for the Development of Tolerable Upper Intake Levels." Dietary Reference Intakes for Vitamin A, Vitamin K, Arsenic, Boron, Chromium, Copper, Iodine, Iron, Manganese, Molybdenum, Nickel, Silicon, Vanadium, and Zinc. Washington, DC: The National Academies Press, 2001.
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Dietary Reference Intakes for Vitamin A, Vitamin K, Arsenic, Boron, Chromium, Copper, Iodine, Iron, Manganese, Molybdenum, Nickel, Silicon, Vanadium, and Zinc
Relevance of Experimental Data
Consideration of the following issues can be useful in assessing the relevance of experimental data.
Animal Data. Some animal data may be of limited utility in judging the toxicity of nutrients because of highly variable interspecies differences in nutrient requirements. Nevertheless, relevant animal data are considered in the hazard identification and dose-response assessment steps where applicable, and, in general, they are used for hazard identification unless there are data demonstrating they are not relevant to human beings, or it is clear that the available human data are sufficient.
Route of Exposure.2 Data derived from studies involving oral exposure (rather than parenteral, inhalation, or dermal exposure) are most useful for the evaluation of nutrients. Data derived from studies involving parenteral, inhalation, or dermal routes of exposure may be considered relevant if the adverse effects are systemic and data are available to permit interroute extrapolation.
Duration of Exposure. Because the magnitude, duration, and frequency of exposure can vary considerably in different situations, consideration needs to be given to the relevance of the exposure scenario (e.g., chronic daily dietary exposure versus short-term bolus doses) to dietary intakes by human populations.
Pharmacokinetic and Metabolic Data
When available, data regarding the rates of nutrient absorption, distribution, metabolism, and excretion may be important in derivation of Tolerable Upper Intake Levels (ULs). Such data may provide significant information regarding the interspecies differences and similarities in nutrient behavior, and so may assist in identifying relevant animal data. They may also assist in identifying life stage differences in response to nutrient toxicity.
In some cases, there may be limited or even no significant data relating to nutrient toxicity. It is conceivable that in such cases,
The terms route of exposure and route of intake refer to how a substance enters the body (e.g., by ingestion, injection, or dermal absorption). These terms should not be confused with form of intake, which refers to the medium or vehicle used (e.g., supplements, food, or drinking water).