Recommended Dietary Allowance (RDA) is the average daily dietary intake of a nutrient that is sufficient to meet the requirement of nearly all (97-98%) healthy persons. DRI’s have replaced and expanded the traditional Recommended Dietary Allowances (RDAs).
The DRIs are actually a set of the following four reference values:
• Recommended Dietary Allowance (RDA) as listed above.
• Adequate Intake (AI) for a nutrient is established when available data are insufficient to set an RDA but are sufficient to estimate an intake that would maintain nutritional adequacy in most people. The AI is based on observed intakes of the nutrient by a group of healthy persons.
• Tolerable Upper Intake Level (UL) is the highest daily intake of a nutrient that is likely to pose no risks of adverse health effects (toxicity) for almost all individuals. As intake above the UL increases, risk increases.
• Estimated Average Requirement (EAR) is the amount of a nutrient that is estimated to meet the requirement of half of all healthy individuals in the population.
Source: http://www.ars.usda.gov/News/docs.htm?docid=10681