FIGURE 9-3 Distribution of reported vitamin C intake from all sources for men and women who smoke aged 19 years and older, from the Third National Health and Nutrition Examination Survey (NHANES III), 1988–1994. The area under the curve represents almost 100 percent of that population (the right tail of the distributions are not shown). Approximately 53 percent of men who smoke and 30 percent of women who smoke have reported total vitamin C intakes (food plus supplements) below the Estimated Average Requirement (EAR) adjusted for the effect of smoking to 110 mg/day for men and 95 mg/day for women. Data have been adjusted for within-person variability (see note below).

NOTE: Nutrient intake from supplements in NHANES III is collected via an instrument similar to a food frequency questionnaire. Thus, the correct method for combining nutrient intake from food (collected with a 24-hour recall) and nutrient intake from supplements to assess total intake is uncertain. For the specific examples shown above, the following process was followed: (1) usual intakes from food were estimated for each individual using the Nusser et al. (1996) approach; (2) self-reported usual intake from supplements were added to obtain an estimate of the individual's total usual intake; and (3) these total usual intakes were compared to the EAR to obtain an estimate of the prevalence of inadequate intakes. This approach may not be optimal because it assumes that the self-reported usual supplement intake has no day-to-day variability. Therefore, the examples may not provide the best estimate of the prevalence of inadequacy of a nutrient, but they still serve to illustrate the use of the EARs when assessing intakes of groups.

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