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Dietary reference intakes (DRI) are a set of reference values for vitamins, minerals, and other nutrients important to human health. DRIs provide guidance about the appropriate amount of each nutrient that should be consumed based on American and Canadian diets. DRIs are specific to age group, gender, and for women, reproductive status.
DRIs are tools intended to be used in planning and assessing diets of individuals and groups. They are based on data that applies to American and Canadian populations and replace previously issued Recommended Dietary Allowances (RDAs) in the United States and Recommended Nutrient Intakes (RNIs) in Canada.
Health is strongly affected by the food that people eat, and proper diet can delay, prevent, or treat certain diseases and disorders. Research on dietary vitamins and minerals in the 1920s and 1930s led to the publication of the first RDAs in 1941 by the Food and Nutrition Board of the National Academy of Sciences. These early RDAs were based on the amount of each vitamin or mineral that was needed to prevent symptoms of the corresponding nutrient-deficiency disease. For example, the RDA for vitamin A was set at a level that would prevent symptoms of night blindness. The availability of RDAs gave a boost to food fortification programs that helped eliminate many vitamin deficiency disorders such as pellagra, which is caused by niacin deficiency.
The RDAs were reviewed about every five years and the values were adjusted as additional research became available, but for many years the underlying assumption remained one of setting dietary intake level of each nutrient to prevent disease. Multi-vitamin dietary supplements have been in use for many years. By the early 1980s single-ingredient dietary supplements, many claiming to boost athletic or sexual performance, increase energy, prevent disease, or control weight, had become much more common. Research on these dietary supplements showed that some vitamins and minerals taken in quantities larger than the RDA appeared to provide benefits to healthy individuals, but the same supplement taken in too large a quantity could be harmful. TheInstitute of Medicine
of the National Academy of Sciences decided that an expanded set of reference values was needed to incorporate this new research and provide better nutrition guidance to both health professionals and consumers. In 1997, in cooperation with nutrition authorities in Canada, they began replacing RDAs (and RNIs in Canada) with the first Dietary Reference Intakes or DRIs.
Components of the DRIs
DRIs cover micronutrients (e.g., vitamins and minerals) essential to human health. Dietary guidance in a different form is also given for macronutrients(e.g., protein, carbohydrates, and fats). The DRIs for vitamins and minerals consist of four values that reflect both the lower and upper daily intake limits beyond which adverse health effects may occur. They also include and an average or recommended daily value meets the health needs of most of the population.
DRIs are intended to apply only to people who appear healthy. They are calculated based on the nutritional needs of each age group and gender: infants 0-6 months and 6-12 months; children ages 1-3 years, 4-8 years, and 9-13 years; adolescents 14-18 years, and adults. The adult group is subdivided into women who are pregnant, women who are breastfeeding, and sometimes into younger and older adults, depending on the nutrient. The values for each nutrient are measured against a specific reference goal. Examples of these goals include preventing symptoms of a nutrient deficiency disease, maintaining normal growth, maintaining a specific level of the nutrient circulating in the blood, or preventing symptoms associated with nutrient excess.
Four reference values make up the DRI for micronutrients:
- Estimated Average Requirement (EAR). The EAR is the average daily intake of a nutrient that will meet the nutritional needs of half the individuals in the group. In other words, if half the healthy children between ages four and eight received the EAR for iron for their age group, about 50% would show signs of iron deficiency and 50% would not.
- Recommended Dietary Allowance (RDA). The RDA is the amount of a nutrient that meets the needs of 97-98% of all healthy individuals within the group. For example, if all children ages 4-8 years old were receiving the RDA for iron for their age group, only one or two of every hundred children would be iron deficient. The RDA is calculated using the EAR and the amount of variability (standard deviation [SD]) of the need for the nutrient within each group. Mathematically RDA = EAR + (2 x SD of the nutrient).
- Average Intake (AI). Calculating the RDA requires that enough information is available to calculate the EAR. This information is not always available because of practical and ethical limitation on experimenting with humans. When insufficient information is available to calculate the RDA, an estimate of the average daily intake is made. Just like the RDA, the AI expected to meet or exceed the nutritional need of almost everyone in the group. Although both the RDA and the AI are intended to give guidance about how much of a particular nutrient a healthy individual in a specific group should, on average, get daily, the AI is an estimate based on experimental evidence and observation, not a defined calculation like the RDA.
Macronutrients are what most people call food— nutrients that provide calories (energy). These include carbohydrates, fat, fatty acids, cholesterol, protein, and amino acids. Fiber is an included nutrient but it does not provide energy. In the body, carbohydrates, proteins, and fats can in some cases be used interchangeably. In addition, it is not possible to link specific quantities of these macronutrients to the prevention or development of chronic diseases such as diabetes and cardiovascular disease. In place of DRIs, the Institute of Medicine has developed Acceptable Macronutrient Distribution Ranges (AMDRs) for energy-yielding nutrients. AMDRs are expressed, not as absolute numbers, but as a percentage of total energy (calorie) intake.
The four components of the DRI are intended to provide more guidance than a single number alone would provide. However, they are not without their critics. Some criticism stems from statistical assumptions made in the calculations. Other criticism is based on the fact that different forms of certain nutrients have a different bioavailability. For example, iron in meat is more easily absorbed than iron in plant foods, and the vitamin E in dietary supplements is more biologically active than vitamin E in food. Although this should not be a source of confusion to healthcare professionals, it can be confusing to the average consumer.
The greatest controversies among experts are over the UL. These center around four areas:
- Very little experimental data is available about the upper limit of certain nutrients in special populations such as children, pregnant women, and elderly individuals
- Some experts are not comfortable with the way the Institute of Medicine derived UL values. Experts point out that in some cases the UL for one subgroup overlaps the RDA for another subgroup and that in other cases the typical intake of certain groups already exceeds the UL with no apparent harmful effects (e.g., iron in young children). The vitamin C UL appear to be especially controversial
- No distinction is made between short-term (acute) and long-term (chronic) overdose of nutrients
- The ULs do not take into consideration genetic diversity of the population and are much less sensitive to the life stage of the individual than RDAs. This is in part because of limited data available for certain age groups
- Much of the data used to determine the UL is based on short-term (a few days) intake information and therefore has a high degree of unreliability. Human experiments with potentially toxic mega doses of nutrients is generally unethical, making an adequate amount of reliable data in the UL range difficult to obtain
DRIs and AMRDs continue to be researched and revised as more data becomes available. Despite the controversy, they offer both healthcare professionals and individuals some guidelines about the benefits and dangers of nutrient consumption.
DRIs are intended as guidelines for population groups, not individuals. Although they give values for daily intake of nutrients, these values are intended to apply over time. Except in cases of acute mega doses, the effects of too much or too little of a nutrient develop gradually over time. In any given day, an individual may eat more or less than the DRI of a particular nutrient and still remain healthy.
DRIs are intended to be applied to a healthy population. Individuals under the supervision of a healthcare professional may be advised to take more or less of particular nutrients than the DRIs indicate. In this situation, the advice of the healthcare professional should be followed.
Nutrients interact with each other and with pharmaceuticals and herbal remedies. These interactions are not entirely understood and may affect the absorption, utilization, and excretion of various vitamins and minerals in ways that change the RDA.
Certain population groups, such as vegans, have dietary needs that may be satisfied only with dietary supplements or very carefully controlled diets.
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Tish Davidson, A.M.