Aspects of this topic are discussed in the following places at Britannica.
...requirement of nearly all (97 to 98 percent) healthy persons in a particular life stage. When the EAR, and thus the RDA, cannot be set due to insufficient scientific evidence, another parameter, the Adequate Intake (AI), is given, based on estimates of intake levels of healthy populations. Lastly, the Tolerable Upper Intake Level (UL) is the highest level of a daily nutrient intake that will...
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