James Penland

You read that the RDA for vitamin C is 60 milligrams per day for adults. So, what does it mean?

Recommended Dietary Allowances (RDAs), established by the Food and Nutrition Board of the National Academy of Sciences' Institute of Medicine, provide nutrition guidance to the general public and health professionals. These numeric values are defined as the levels of intake of essential nutrients that are judged to be adequate to meet the known needs of practically all healthy persons.

In addition to providing information for labels on food, RDAs are used for many other purposes. Institutions use the RDAs to plan healthful diets for schools, prisons, hospitals and nursing homes. Industry uses them to develop new food products. Policy makers (such as program administrators, government officials) use them to evaluate and improve food supplies to meet national needs, and health workers (such as dieticians) use dietary guidelines to provide nutrition education.

In 1995, the Food and Nutrition Board decided that a new, more comprehensive approach was necessary to setting dietary guidelines. New research was showing the importance of higher intakes of some nutrients for promoting health (preventing chronic disease) and performance; there was tremendous growth in food fortification and the use of dietary supplements; and the existing RDAs did not adequately distinguish guidelines for groups and populations from those for individuals.

So the Board replaced and expanded the current RDAs with a series of reference values called Dietary Reference Intakes (DRIs) to provide recommended nutrient intakes for use in a variety of settings, such as schools, prisons, hospitals, and nursing homes. The DRIs are actually a set of four reference values.

• 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.
• Adequate Intake (AI) for a nutrient is similar to the ESADDI and is only established when an RDA cannot be determined. Therefore a nutrient either has an RDA or an AI. 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 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.

Each of these reference values distinguishes between gender and different life stages. RDAs, AIs and ULs are dietary guidelines for individuals, whereas EARs provide guidelines for groups and populations. In addition, factors that might modify these guidelines, such as bioavailability of nutrients from different sources, nutrient-nutrient and nutrient-drug interactions, and intakes from food fortificants and supplements, are incorporated into the guidelines in much greater detail than previously.

In January 2001, the Food and Nutrition Board of the National Academy of Sciences' Institute of Medicine released intake recommendations for vitamins A and K and 12 minerals. The new Dietary Reference Intakes (DRIs) for Micronutrients covers the minerals arsenic, boron, chromium, copper, iodine, iron, manganese, molybdenum, nickel, silicon, vanadium and zinc. DRIs for the minerals calcium, fluoride, magnesium, phosphorus, and selenium were released in earlier reports.

Cited in the report were more than 50 research publications based on studies conducted at our own Grand Forks Human Nutrition Research Center, part of the U.S. Department of Agriculture's Agricultural Research Service.

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