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Dietary Reference Intakes (DRIs)

New Guidelines for Calcium and Related Nutrients

Stephen Barrett, M.D.

The Dietary Reference Intakes (DRIs) are nutrient-based reference values for use in planning and assessing diets and for other purposes. They are intended to replace the Recommended Dietary Allowances (RDAs) that have been published since 1941 by the National Academy of Sciences. They are being determined by the Standing Committee on the Scientific Evaluation of Dietary Reference Intakes of the Food and Nutrition Board, Institute of Medicine (IOM), National Academy of Sciences, with help from Health Canada. The IOM is a private, nonprofit organization that provides health policy advice under a congressional charter granted to the National Academy of Sciences.

Each of the ten editions of the RDAs was a single report. The DRI values will comprise seven reports. The first one, published in August 1997, covers nutrients related to bone health (calcium, phosphorus, magnesium, vitamin D, and fluoride). Subsequent volumes will consider: (1) folate and other B vitamins; (2) antioxidants (e.g., vitamins C and E, selenium); (3) macronutrients (e.g., protein, fat, carbohydrates); (4) trace elements (e.g., iron, zinc); (5) electrolytes and water; and (6) other food components (e.g., fiber, phytoestrogens). The first report was funded by the FDA, the USDA Agricultural Research Service, and the National Heart, Lung, and Blood Institute. The IOM hopes that all of the reports will be released by the year 2000.

A New Approach

The RDAs have served as the benchmark of nutritional adequacy in the United States. More than 20 years ago, they were defined as: "The levels of intake of essential nutrients that, on the basis of scientific knowledge, are judged by the Food and Nutrition Board to be adequate to meet the known nutrient needs of practically all healthy persons."

Scientific knowledge about the roles of nutrients has expanded dramatically since the RDAs were first published. Many studies have examined relationships between diet and chronic disease. The Food and Nutrition Board has responded to these developments by changing its basic approach to setting nutrient reference values.

The DRIs reflect a shift in emphasis from preventing deficiency to decreasing the risk of chronic disease through nutrition. The RDAs were based on the amounts needed to protect against deficiency diseases. Where adequate scientific data exist, the DRIs will include levels that can help prevent cardiovascular disease, osteoporosis, certain cancers, and other diseases that are diet-related. Instead of a single category, the DRIs will encompass at least four:

1. Estimated Average Requirement (EAR): The intake that meets the estimated nutrient need of 50% the individuals in a specific group. This figure will be used as the basis for developing the RDA and can be used by nutrition policy-makers to evaluate the adequacy of nutrient intakes for population groups.

2. Recommended Dietary Allowance (RDA): The intake that meets the nutrient need of almost all (97 to 98%) of the healthy individuals in a specific age and gender group. The RDA should be used in guiding individuals to achieve adequate nutrient intake aimed at decreasing the risk of chronic disease. It is based on estimating an average requirement plus an increase to account for the variation within a particular group. The amount of scientific evidence available allowed the DRI committee to calculate RDAs for phosphorus and magnesium. If individual variation in requirements is well defined, the RDA is set at 2 standard deviations above the EAR, which means it should be high enough to meet the needs of at least 97­98% of the population. If sufficient data are not available, the RDA is set at 1.2 x EAR.

3. Adequate Intake (AI): When sufficient scientific evidence is not available to estimate an average requirement, Adequate Intakes (AIs) will be set. These are derived though experimental or observational data that show a mean intake which appears to sustain a desired indicator of health, such as calcium retention in bone. The AIs should be used as a goal for individual intake where no RDAs exist. The DRI committee set AIs for calcium, vitamin D, and fluoride.

4. Tolerable Upper Intake Level (UL): The maximum intake by an individual that is unlikely to pose risks of adverse health effects in almost all healthy individuals in a specified group. The UL is not intended to be a recommended level of intake, and there is no established benefit for individuals to consume nutrients at levels above the RDA or AI. The term "tolerable upper intake level" was chosen to avoid implying a possible beneficial effect. For most nutrients, it refers to total intake from food, fortified food, and supplements.

What They Mean

The DRIs are intended to apply to the healthy general population. RDAs and AIs are dietary intake values that should minimize the risk of developing a condition or sign that is associated with that nutrient in question and that has a negative functional outcome. They refer to average daily intake over one or more weeks. They should not necessarily be expected to replete individuals who are already malnourished and may not be adequate for disease states marked by increased requirements. Individuals known to have diseases that greatly increase requirements, or who have increased sensitivity to developing adverse effects associated with higher intakes, should be guided by qualified medical and nutrition personnel.

The committee cautioned that nutrient intake less than the RDA does not necessarily mean that a given individual is not getting enough of that nutrient. Healthy individuals who meet the AI have a low risk of inadequate intake. However, an intake well below the RDA or AI would be a reason to assess the individual's nutritional status through laboratory testing or clinical examination. The IOM expects future publications to provide more detailed advice on how the DRIs should be interpreted and used.

Revised Values

In many cases, various levels of intake can have different benefits. One level may be related to the risk of deficiency, for example, while another level can influence the risk of chronic disease for that nutrient. For this reason, "nutrient adequacy" should be should be expressed in terms of "Adequate for what?" For this reason, the DRIs are far more elaborate than the RDAs and cannot be expressed in a simple table of values.

• Calcium recommendations were set at levels associated with maximum retention of body calcium, since bones that are calcium rich are known to be less susceptible to fractures. The other factors known to affect bone retention of calcium and risk of osteoporosis include high rates of growth in children during specific periods, hormonal status, exercise, genetics, and other diet components. The new report advises Americans and Canadians at risk for osteoporosis to consume between 1000 and 1300 milligrams of calcium per day. These values (AIs) are higher than the 1989 RDAs, which ranged from 800 to 1200. The adult UL for calcium is 2.5 grams per day.
• Phosphorus, important for bone and soft tissue growth, is so prevalent in various foods that near starvation or a metabolic disorder is required to produce deficiency. Different from former RDAs, phosphorus values in the report are not derived in relation to calcium. The values recommended are considered sufficient to support normal bone growth and metabolism at various ages. The new RDAs are about 12% lower than the 1989 RDAs.
• Magnesium works with many enzymes to regulate body temperature, allow nerves and muscles to contract, and synthesize proteins. Although some researchers have argued that magnesium recommendations should be based on relationships with the risk of cardiovascular disease, the report does not find enough data available at this time to do so. The levels recommended, although somewhat higher, do not differ substantially from the 1989 RDAs but are higher than current Canadian recommendations.
• Vitamin D used by the body comes mostly through exposure to the sun. Vitamin D deficiency can exacerbate osteoporosis and other bone problems in adults. Dietary intake of vitamin D is unnecessary for people who spend adequate amounts of time in the sun. The levels recommended in the report are estimated to provide enough vitamin D even for individuals with limited sun exposure. The AIs of 10 micrograms from age 51 to 70 and 1 micrograms over age 70 are higher than their 1989 counterparts. The adult UL for vitamin D is 50 micrograms (2000 IU) per day.
• Fluoride is found naturally in some community water systems, and is added to water in other areas to reduce dental decay. The levels recommended in the DRIs have been shown to reduce tooth decay without causing marked fluorosis, a discoloration of the teeth that could occur in children who use dental products with fluoride in addition to fluoridated water. The AIs for fluoride are similar to the corresponding values (ESADDIs) in the 1989 report. The American Dental Association, the American Academy of Pediatrics, and the Canadian Paediatric Society recommend that children living in nonfluoridated communities take fluoride supplements because the required amount is unlikely to be provided by food. The amounts recommended for infants and children have been lowered during the past few years because of concern about fluorosis, a cosmetic defect that most commonly involves white patches that are barely visible on the teeth.

Except for fluoride, the greatest disparity between recommended values and current dietary patterns is in calcium, which comes primarily from dairy products. Surveys indicate that many do not consume the amount of calcium recommended in the report. Calcium intake can be increased by consuming more lowfat or nonfat dairy products or fortified food products or by taking supplements. The report states that taking supplements may be appropriate for those at high risk of health problems due to low calcium intake.

The report also states: (a) unfortified foods are advantageous for meeting the RDAs and AIs because they provide other food components for which RDAs and AIs may not be determined; (b) food fortification can increase or maintain nutrient intakes without major changes in food habits; and (c) nutrient supplemention may be desirable for some people.

For Further Information

The full DRI report -- Dietary Reference Intakes: Calcium, Phosphorus, Magnesium, Vitamin D, and Fluoride -- can be purchased by calling (800) 624-6242; sending $39 to the National Academy Press, 201 Constitution Ave, N.W., Washington, DC 20418; or ordering it at a discount online. The full text can also be read online, although the process is cumbersome.