The development of DRIs expands on the periodic reports called Recommended Dietary Allowances, which have been published since 1941 by the National Academy of Sciences. It is expected that as additional groups of nutrients and food components are reviewed over the next few years, the process and initial models developed will evolve and be further refined. As new information or processes develop, reference intakes will be periodically reassessed in keeping with this evolving process.
The Recommended Dietary Allowance (RDA) is the average daily dietary intake level that is sufficient to meet the nutrient requirement of nearly all (97 to 98 percent) healthy individuals in a particular gender and life stage group (life stage considers age and, when applicable, pregnancy or lactation).
The process for setting the RDA depends on being able to set an Estimated Average Requirement (EAR). That is, the RDA is derived from the nutrient requirement so if an EAR cannot be set, no RDA will be set. The EAR is the daily intake value of a nutrient that is estimated to meet the nutrient requirement of half the healthy individuals in a life stage and gender group. Before setting the EAR, a specific criterion of adequacy is selected, based on a careful review of the literature. When selecting the criterion, reduction of disease risk is considered along with many other health parameters. The RDA is set at the EAR plus twice the standard deviation (SD) if known (RDA = EAR + 2 SD); if data about variability in requirements are insufficient to calculate an SD, a coefficient of variation for the EAR of 10 percent is ordinarily assumed (RDA = 1.2 x EAR).