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DRI DIETARY REFERENCE INTAKES FOR Vitamin C, Vitamin E, Selenium, and Carotenoids
FIGURE 1-1 Dietary reference intakes. This figure shows that the Estimated Average Requirement (EAR) is the intake at which the risk of inadequacy is 0.5 (50%) to an individual. The Recommended Dietary Allowance (RDA) is the intake at which the risk of inadequacy is very small —only 0.02 to 0.03 (2% to 3%). The Adequate Intake (AI) does not bear a consistent relationship to the EAR or the RDA because it is set without being able to estimate the average requirement. It is assumed that the AI is at or above the RDA if one could be calculated. At intakes between the RDA and the Tolerable Upper Intake Level (UL), the risks of inadequacy and of excess are both close to 0. At intakes above the UL, the risk of adverse effects may increase.
If data about variability in requirements are insufficient to calculate an SD, a coefficient of variation (CV EAR) of 10 percent will ordinarily be assumed and used in place of the SD. Because
CV EAR = SD EAR /EAR, and
SD = (EAR × CV EAR);
the resulting equation for the RDA is
RDA = EAR + 2 (0.1 × EAR), or
RDA = 1.2 × EAR.
If the nutrient requirement is known to be skewed for a population, other approaches will be used to find the ninety-seventh to ninety-eighth percentile to set the RDA.
The assumption of a 10 percent CV is based on extensive data on the variation in basal metabolic rate (FAO/WHO/UNA, 1985; Garby and Lammert, 1984), which contributes about two-thirds of the daily energy expenditure of many individuals residing in Canada