The Recommended Dietary Allowance (RDA) for vitamins and minerals has been prepared by the Food and Nutrition Board of the National Research Council since 1941. These guidelines were originally developed to reduce the rates of severe nutritional deficiency diseases, such as scurvy (deficiency of vitamin C), pellagra (deficiency of niacin), and beriberi (deficiency of vitamin B1). Another critical point is that the RDAs were designed to serve as the basis for evaluating the adequacy of diets of groups of people, not individuals, because individuals vary too widely in their nutritional requirements. As stated by the Food and Nutrition Board, "Individuals with special nutritional needs are not covered by the RDAs." Statistically speaking, RDAs prevented deficiency diseases in 97 percent of a population, but there was no scientific basis that they met the needs of any individual person.
In 1993, the Food and Nutrition Board put the RDA revision process into motion by holding a symposium and asking for scientific and public comment on how the RDAs should be revised. Utilizing feedback from this conference and other sources, the Food and Nutrition Board developed an ambitious framework for revamping the old RDAs. Rather than having a single group of scientists revise the existing set of RDAs, they had expert panels review nutrient categories in much more detail than had ever been done before. The Food and Nutrition Board partnered with Health Canada, the Canadian government agency responsible for nutrition policy, and the two groups jointly appointed the Standing Committee on the Scientific Evaluation of Dietary Reference Intakes of the Food and Nutrition Board.
As a result, not only did the definition of RDAs change, but three new values were also created: the Estimated Average Requirement (EAR), the Adequate Intake (AI), and the Tolerable Upper Intake Level (UL). All four values are collectively known as Dietary Reference Intakes, or DRIs. The DRIs reflect a shift in emphasis from preventing deficiency to decreasing the risk of chronic disease through nutrition and proper nutritional supplementation. The RDAs were based on the amounts needed to protect against deficiency diseases. Where adequate scientific data exists, the DRIs strive to include levels that can help prevent certain cancers, cardiovascular disease, osteoporosis, and other diseases that are diet-related.