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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
for setting ULs grew out of the increased fortification of foods with nutrients and the use of dietary supplements by more people and in larger doses. The UL applies to chronic daily use. As in the case of applying AIs, professionals should avoid very rigid application of ULs and first assess the characteristics of the individual and group of concern, such as source of nutrient, physiological state of the individual, length of sustained high intakes, and so forth.
For some nutrients such as vitamin K, arsenic, chromium, and silicon, data are not sufficient for developing a UL. This indicates the need for caution in consuming amounts greater than the recommended intakes; it does not mean that high intakes pose no risk of adverse effects.
The safety of routine, long-term intake above the UL is not well documented. Although members of the general population should be advised not to routinely exceed the UL, intake above the UL may be appropriate for investigation within well-controlled clinical trials. Clinical trials of doses above the UL should not be discouraged as long as subjects participating in these trials have signed informed consent documents regarding possible toxicity and as long as these trials employ appropriate safe monitoring of trial subjects.
Determination of Adequacy
In the derivation of the EAR or AI, close attention has been paid to the determination of the most appropriate indicators of adequacy. A key question is, Adequate for what? In many cases, a continuum of benefits may be ascribed to various levels of intake of the same nutrient. One criterion may be deemed the most appropriate to determine the risk that an individual will become deficient in the nutrient whereas another may relate to reducing the risk of chronic degenerative disease, such as diabetes mellitus or osteoporosis.
Each EAR and AI is described in terms of the selected criterion. The potential role of the nutrient in the reduction of disease risk was considered in developing the EARs. With the acquisition of additional data relating intake to chronic disease or disability, the choice of the criterion for setting the EAR may change.
PARAMETERS FOR DIETARY REFERENCE INTAKES
Life Stage Groups
The life stage groups described below were chosen by keeping in mind all the nutrients to be reviewed, not only those included in