James G. Penland

You're probably familiar with the Recommended Dietary Allowances (RDAs) established by the Food and Nutrition Board of the National Academy of Sciences. These numerical values provide nutrition guidance to health professionals and to the general public. You may have heard, for example, that the RDA for vitamin C is 60 milligrams per day for adults. RDAs 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 use them to evaluate and improve food supplies to meet national needs, and health workers use them to provide nutrition education.

Since 1941, when the first RDAs were published, they have been updated 10 times. The most recent revision was in 1989 when RDAs were determined for protein, 11 vitamins, and 7 minerals. RDAs were set for different age groups, for men and women, and for pregnant and nursing mothers. The board also established Estimated Safe and Adequate Daily Dietary Intakes (ESADDIs) for 7 nutrients where available data were insufficient to set an RDA.

In 1995, the Food and Nutrition Board deemed that a new, more comprehensive approach was necessary to setting dietary guidelines. Why? 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 Dietary Reference Intakes (DRIs) to provide recommended nutrient intakes for use in a variety of settings. 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.

Establishing the DRIs is a huge undertaking that will require more than five years to complete and involve several panels of independent experts to evaluate the scientific data. Three panels have already completed their work; two are currently meeting.

Once the initial DRIs are established, they will be regularly updated to reflect new findings, such as those coming from the Grand Forks Human Nutrition Research Center. In fact, our Center is closely involved in establishing these new guidelines. Last April, six of our scientists provided research data and expert testimony to the Food and Nutrition Board on arsenic, boron, copper, iron, nickel, silicon, vanadium and zinc. The author is currently participating as a member of the DRI Panel on Micronutrients.

As new DRIs are released, just remember that they include RDAs, AIs, ULs, and EARs. Individuals should pay particular attention to RDAs (or AIs) as a goal for average daily intake and ULs as an indicator of highest safe intake. EARs will be used by dietitians and others planning diets, developing new foods, and setting policies for food supplies for groups and populations.

For additional information about DRIs, visit the following web pages: www.eatright.org or www.nas.edu.

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