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Dietary Reference Intakes for Vitamin A, Vitamin K, Arsenic, Boron, Chromium, Copper, Iodine, Iron, Manganese, Molybdenum, Nickel, Silicon, Vanadium, and Zinc
Estimated Average Requirement (EAR) estimates the median of a distribution of requirements for a life stage and 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 or inadequacy. Furthermore, the rarity of having precise and representative data on the usual intake of an individual adds further uncertainty to the evaluation of an individual’s dietary adequacy.
Dietary assessment methods have several inherent inaccuracies. One is that individuals underreport their intakes (Mertz et al., 1991; Schoeller, 1999), and it appears that obese individuals often do so to a greater extent than do normal-weight individuals (Heitmann and Lissner, 1995). Currently, a method for adjusting intakes based on underreporting by individuals is not available and much work is needed to develop an acceptable method.
Furthermore, large day-to-day variations in intake, which occur for almost all individuals, mean that it often takes a prohibitively large number of days of intake measurement to approximate usual intake (Basiotis et al., 1987). As a result, substantial caution must be used when interpreting nutrient assessments based on self-reported dietary data covering relatively few days of intake. Data on nutrient intakes should almost always be interpreted in combination with typical food usage patterns.
An approach for using data from dietary records or recalls to estimate the likelihood that an individual’s nutrient intake is adequate is presented in the report Dietary Reference Intakes: Applications in Dietary Assessment (IOM, 2000). This approach, which is appropriate for nutrients with symmetrical requirement distributions, requires the following data:
the individual’s mean nutrient intakes during a given number of days;
the day-to-day standard deviation of intakes for each nutrient of interest, as estimated from larger data sets for the appropriate life stage and gender group;
the EAR; and
the standard deviation of the nutrient requirement in the individual’s life stage and gender group.
From this information, a ratio is computed that compares the magnitude of difference between the individual’s intake and the EAR to an estimate of variability of intake and requirements. The