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DRI DIETARY REFERENCE INTAKES FOR Vitamin C, Vitamin E, Selenium, and Carotenoids
als. The Estimated Average Requirement (EAR) estimates the median requirement of a distribution of requirements for a life stage or gender group, but it is not possible to know where an individual falls on this distribution without further physiological or biochemical measures. Thus, from dietary data alone, it is only possible to estimate the likelihood of nutrient adequacy. Furthermore, it is rare to have precise and representative data on usual intake of an individual, which adds additional uncertainty to the evaluation of an individual's dietary adequacy. Thus, true nutrient status can usually be determined only by obtaining physiological and biochemical data for the individual, and not from dietary assessment alone.
There are a number of inherent inaccuracies in dietary assessment methods. One is that individuals often underreport their intakes (Briefel et al., 1997; Mertz et al., 1991), and it appears that obese individuals do so to a greater extent than normal-weight individuals (Heitmann and Lissner, 1995). Furthermore, large day-to-day variations in intake, which occur for almost all individuals, necessitate many days of measurement to approximate usual intake. As a result, substantial caution must be used when interpreting nutrient assessments based on self-reported dietary data covering relatively few days of intake. Given the difficulties in accurately estimating usual intake, as well as the variance in requirements, a qualitative interpretation is recommended as described below:
If usual intake of an individual is greater than or equal to the Recommended Dietary Allowance (RDA), there is little likelihood that intake is inadequate. Intake at this level is expected to be inadequate for fewer than 2 to 3 percent of individuals (IOM, 1997, 1998).
If usual intake is between the RDA and the EAR, there is a great deal of uncertainty about whether that intake is inadequate and additional information about the individual may be needed. Usual intake between the RDA and the EAR is inadequate for about 3 to 50 percent of the individuals in the life stage group. If these individuals maintained intakes at this level over a prolonged time period, they might demonstrate the signs of inadequacy used to establish the EAR. For example, inadequate intake of vitamin C would lead to low ascorbate saturation of neutrophils.
If usual intake is less than the EAR, there is a high likelihood that intake is inadequate. Usual intake at the EAR is expected to be inadequate for at least 50 percent of individuals.
Because usual intakes are so difficult to measure, and because an individual's actual requirement is usually unknown, evaluation