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RDA AND OTHER MEASURES
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HEALTHY NUTRIENT LEVELS IN THE DIET
Various terms are in use concerning dietary nutrient levels for maintaining adequate health. The most widely known term is the RDA --
Recommended Dietary Allowance (RDA) --
The average daily dietary intake level, as judged by the Food and Nutrition Board of the U.S. National Research Council / National Academy of Sciences, that is sufficient to meet the known nutrient requirement of nearly all (97 to 98 percent) of the healthy individuals in a group. RDA levels are categorized by weight, height, sex and age. Originally, the levels were based on extensive study of the diets of a large group of normally healthy people.
Note that RDA levels and the newer RDI values (see below) are generalizations applying to normal, healthy groups of people. Individual needs vary from individual to individual, and in response to condition of health or disease, type of diet, level of exercise, and use of therapeutic drugs or injurious substances.
Owing to advances in measurement techniques and accumulation of new data, a new set of measures has been adopted. Given that RDA values were determined from earlier studies, and that new studies provide much additional information, measures based on the newer data are deliberately given new names. The principal measure based on the newer data is the RDI level --
Recommended Daily Intake (RDI) --
The Reference or Recommended value for Daily Intake of an essential nutrient and/or energy source that will maintain health in practically all healthy individuals on average. RDI values are not health policy recommendations or dietary guidelines for specific individuals. Minimal values for nutrient levels from all the weight, height, sex and age groups included in RDA and newer studies were used to establish RDI levels. RDI levels (and, in the past, the RDA levels) and percentage daily intake levels derived from RDI levels are put on food box labels in compliance with U.S. Food and Drug Administration regulations.
Dietary Reference Intake (DRI) --
A reference value that is a quantitative estimate of nutrient intake, useful for planning and assessing diets for healthy people. DRI values incorporate as reference values both recommended daily intakes (RDI) and tolerable upper intake levels (ULs) (see above and below for definitions of RDI and UL). Although DRI values are based on data, the data are often scanty or drawn from studies that had limitations in addressing the question. Thus, scientific judgment is required in setting DRI values.
RDI and DRI values expand on and replace the Recommended Dietary Allowance (RDA) levels, reflecting increased use of statistically validated methods to assess reference intakes.
In addition to RDI and DRI, new measures include Adequate Intake (AI), Tolerable Upper Intake Level (UL), and Estimated Average Requirement (EAR). These measures are based on extensive data but also require scientific judgment.
Adequate Intake (AI) --
An intake level based on observed or experimentally determined approximations of nutrient intake by a group (or groups) of healthy people. Used when an RDA cannot be determined.
Tolerable Upper Intake Level (UL) --
The highest level of daily nutrient intake that is likely to pose no risks of adverse health effects to almost all individuals in the general population. UL levels are based on extensive study of a large group of people.
A panel of experts convened by the Institute of Medicine has determined the DRI for a series of nutrients. Major new approaches and findings include recommendations for vitamin A, vitamin K, arsenic, boron, chromium, copper, iodine, iron, manganese, molybdenum, nickel, silicon, vanadium, and zinc. An extensive report is available online at http://books.nap.edu/books/0309072794/html/1.html, titled "National Academy Press, Dietary Reference Intakes for Vitamin A, Vitamin K, Arsenic, Boron, Chromium, Copper, Iodine, Iron, Manganese, Molybdenum, Nickel, Silicon, Vanadium, and Zinc (2001)."
National Academy Press --
"The National Academy Press (NAP) was created by the National Academies to publish the reports issued by the National Academy of Sciences, the National Academy of Engineering, the Institute of Medicine, and the National Research Council, all operating under a charter granted by the Congress of the United States. NAP publishes over 200 books a year on a wide range of topics in science, engineering, and health, capturing the most authoritative views on important issues in science and health policy. The institutions represented by NAP are unique in that they attract the nation's leading experts in every field to serve on their blue ribbon panels and committees. For definitive information on everything from space science to animal nutrition, you have come to the right place."
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