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Major new approaches and findings in this report include the following:

  • The establishment of new estimates for the conversion of provitamin A carotenoids to vitamin A: 1 μg retinol activity equivalent (μg RAE) is equal to 1 μg all-trans-retinol, 12 μg β-carotene, and 24 μg α-carotene or β-cryptoxanthin. This recognizes that 50 percent less bioconversion of carotenoids to vitamin A occurs than was previously thought, a change that means twice as much provitamin A-rich carotenoids contained in green leafy vegetables and certain fruits are required to provide a given amount of vitamin A activity. Given possible future changes in equivalency, weight of carotenoids should be given in food tables.

  • The establishment of RDAs for copper and molybdenum.

  • The establishment of Tolerable Upper Intake Levels (ULs) for vitamin A, boron, copper, iodine, iron, manganese, molybdenum, nickel, vanadium, and zinc.

  • Research recommendations for information needed to advance understanding of human micronutrient requirements and the adverse effects associated with intake of higher amounts.


Dietary Reference Intakes (DRIs) are reference values that are quantitative estimates of nutrient intakes to be used for planning and assessing diets for apparently healthy people. They include not only Recommended Dietary Allowances (RDAs) but also three other types of reference values (see Box S-1). Although the reference values are based on data, the data were often scanty or drawn from studies that had limitations in addressing the question. Thus, scientific judgment was required for evaluating the evidence and in setting the reference values, and that process is delineated for each nutrient in Chapters 4 through 13.

Recommended Dietary Allowances

The process for setting the RDA depends on being able to set an Estimated Average Requirement (EAR). Before the EAR is set, a specific criterion of adequacy is selected on the basis of a careful review of the literature. In the selection of the criterion, reduction of disease risk is considered along with many other health parameters.

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