The Recommended Dietary Allowances (RDA) provide the essential-nutrient intake levels required to meet the known nutritional needs of most (97-98%) healthy persons in specific age and gender groups. The RDA is set two standard deviations above the estimated mean requirement, and has been developed by the Food and Nutrition Board of the National Academy of Sciences. The last RDA released was in 1989.
The RDA are currently under revision; values for certain nutrients have been released periodically over the past few years. The new recommendations are called Dietary Reference Intakes (DRI), and include four levels of values: 1) Recommended Dietary Allowances (RDA); 2) Adequate Intakes (AI); 3) Tolerable Upper Intake Level (UL); and 4) Estimated Average Requirement (EAR).
Recommended Dietary Allowances have the same meaning in the new revision as in the previous version. The RDA are meant to be used as a goal for dietary intake for individuals. The RDA are not necessarily intended to be used for assessing the diets of individuals or groups, or planning for groups, although that is how they are most often used. Table 2 provides 1998 RDA for those nutrients that have revised values.
Adequate intake values are set for nutrients for which no EAR has been set. These values are based on observation or experimentation, and measure the average intake of a population that appears to sustain a nutritional state such as normal circulating nutrient values or growth. Table 3 below contains the AI for those nutrients for which a value has been allotted.
The Estimated Average Requirement is the nutrient-intake value that is estimated to meet the requirement in 50% of the individuals in an age and gender group. The EAR is used in setting the RDA. The EAR for selected nutrients is shown in Table 4, below.
The Tolerable Upper Intake Level is the maximal level of nutrient intake that will not pose risks of adverse health effects in most individuals. The UL do not imply, however, that a beneficial effect will occur if that level of nutrient is consumed.