National nutrition and public health policies: issues related to bioavailability of nutrients when developing dietary reference intakes.

Dietary reference intakes (DRI), like its predecessor, the recommended dietary allowances (RDA) and the Recommended Nutrient Intakes (RNIs), are reference values, based on the best scientific evidence available. They serve as reference amounts of specific nutrients and food components for use in assessing the adequacy of and in planning for nutritious diets. They have been used for over 50 y as the basis for national nutrition monitoring and intervention programs in the United States, Canada, and other countries and as the basis for dietary guidance developed for both individuals and for targeted groups of people. Thus, although not developed for specific policy applications, they have represented the best scientific perspectives regarding what should be the basis for nutrition and public health policy related to foods and supplements. In determining DRIs, as was the case with the RDA, significant attention must be paid to the form of the nutrient or food component that is evaluated. Research conducted to determine how much of a nutrient is needed must evaluate the chemical form provided, the matrix in which it is given and the effect of other food components on absorption and/or utilization. Because the DRI recommendations will be used in population-wide policy development, assumptions must be made explicitly about what is expected for all of these factors in a typical diet. At the same time, where data exist relative to nontypical but potentially very significant effects on bioavailability, these must also be delineated to be of use in a variety of settings. Finally, one of the most important aspects of determining bioavailability in developing reference intakes is that as new information emerges, new complexities enter into the process. As more chemical complexes of nutrients and food components become available in the marketplace, new bioavailability factors may need to be established. Examples of such changes exist in the DRI reports already published for vitamin B-12 and folate and in previous RDA for iron and protein. It is often the different assumptions related to bioavailability that alter the reference intakes used as the basis for public health policy in different countries, rather than the basic science from which the recommendation is derived.