RDAs hung out to DRI.

Abstract

As members of the nutrition community, we will soon encounter a new set of abbreviations. The National Food Board is updating and clarifying the Recommended Dietary Allowances (RDAs). The new system is called Daily Recommended Intakes (DRIs). The DRIs will augment, clarify, and add rationale to the previous system. In the long run, use of the DRIs should improve the care of patients. The RDAs were first published in 1941. War rationing was in progress. Physicians and nutritionists were becoming aware of recently described, nutritionally related deficiency diseases. The recommendations were needed to set minimum standards to avoid deficiency diseases in large population groups, including personnel in the military, school children, and workers who supported the war effort. The RDAs were intended to supply adequate amounts of nutrients to support the needs of almost the whole pediatric and adult population. The purpose of the RDAs was quite restricted and different from the way in which they are presently used. Because the RDAs were the most widely available standards, their use spread quickly, and they continue to be used in many situations for which they were not originally intended. Chief among these uses is the calculation of nutritional needs for individual patients. The RDAs have gone through 10 revisions. The last complete revision was published in 1989. Over time, problems with the RDAs have become increasingly apparent. The original definition uses the term adequate amount; however, this definition does not specify which goal is attained by an “adequate amount” of a particular nutrient. The originators of the RDAs were anxious to avoid nutrient-deficiency diseases, such as rickets, scurvy, and pellagra, but the amount that prevents disease may not be adequate to promote optimal health (as with iron depletion and iron-deficiency anemia). The original RDAs also did not address the issue of toxicity. For many nutrients and micronutrients, there is a safe range rather than merely an adequate amount (for example, vitamin A and selenium). Another difficulty with the definition of RDAs lies in the phrase “almost the whole population.” Because the purpose of the RDAs was to set standards that would avoid deficiency diseases in large groups, it made sense to set the RDAs high: two standard deviations above the mean was chosen. When making recommendations for total energy intake, however, it is clearly not optimal to recommend a level that exceeds the needs of almost everyone. A final issue regarding the RDAs is that they are based on a high level of scientific evidence. That is, there must be excellent scientific evidence of the need for a nutrient before an RDA is established. For many nutrients, such a compelling amount of evidence is not available, but some recommendation still may be appropriate. For these reasons, the present Committee of the National Food Board has undertaken a wide-ranging expansion of the RDA system. Daily Recommended Intake (DRI) is an umbrella term that includes four other terms: the Estimated Average Requirement (EAR), the Recommended Daily Allowance (RDA), Adequate Intake (AI), and a tolerable Upper Limit (UL). The EAR is based on strong scientific evidence establishing the average requirement of a nutrient for a population. The EAR is used as the basis for calculating the RDA. The RDA is the amount of a nutrient that is adequate for 97% to 98% of a population. Because the RDA is calculated from the EAR, if there is insufficient scientific evidence to establish an EAR, no RDA can be determined. Adequate intake is an approximation of the nutrient intake of healthy individuals, either observed or determined. The tolerable UL is the highest intake of a nutrient that is likely to pose no threat to almost all the individuals in a population. Figure 1 is a model for a nutrient DRI. It assumes a Gaussian distribution for both risk of nutrient inadequacy and risk of toxicity. These new recommendations should help in our daily work of trying to optimize individual patient's nutrient intakes. They should also be useful in studies to determine an adequate intake for population groups. Of importance, the recommendations should allow for incorporation of toxicity into thinking about nutrient and micronutrient requirements. Further information and updates on the DRI project are available on-line at www2.nas.edu/fnb.