Using Dietary Reference Intake-based Methods to Estimate the Prevalence of Inadequate Nutrient Intake Among School-aged Children
Section snippets
Subjects
The analysis in this report is based on data from 2,692 children aged 6 to 18 years who completed 2 days of dietary intake interviews in the 1994 to 1996 CSFII (8), the most recent data source available when the study began. The CSFII is based on 3 independently drawn, nationally representative 1-year samples of the noninstitutionalized population of the United States. The samples were drawn using stratified, clustered, multistage techniques, with oversampling of low-income persons. Table 1
EAR Cut-point Method
To assess the extent of inadequate intake of nutrients other than iron and calcium, we used the EAR cut-point method proposed by the Institute of Medicine (3). This method entails estimating the proportion whose usual intake of the nutrient was below the EAR (2), (7), (9), (10) for age and gender. To account for day-to-day variation in nutrient intake from food, we used the Software for Intake Distribution Estimation (SIDE) Program (version 1.0, 1996, Department of Statistics and Center for
Probability Approach
To estimate the prevalence of inadequate intake of iron among children, we did not use the EAR cut-point method because 1of the assumptions of this method was not satisfied (3). In particular, the distribution of iron requirements cannot be assumed to be symmetric around its mean, especially among teenaged girls. Instead, we used the probability approach, which is based on the relationship between the distribution of usual iron intake and the full distribution of iron requirements. We obtained
Distribution of Intake
Calcium For calcium, only an Adequate Intake (AI) value has been set by the Institute of Medicine (9). Because guidance has not been provided for using the AI to assess the adequacy of intake by group (3), we did not estimate the percentages of children with intakes below a standard based on the AI. Instead, we simply estimated the full distribution of usual calcium intake, relative to the AI, for all children and for key subgroups of children. This method of presenting the data enables one to
Statistical Analysis
To determine whether differences between groups of children existed with respect to background characteristics or the percentage with inadequate intakes, we conducted χ2 tests. In particular, we tested the hypothesis that these background characteristics and intakes were the same across the 6 gender and age groups in our sample of males aged 6 to 8 years, females aged 6 to 8 years, males aged 9 to 13 years, females aged 9 to 13 years, males aged 14 to 18 years, and females aged 14 to 18 years.
Results
Nutrients for Which an Estimated Average Requirement Has Been Set
Table 2 shows the percentages of all children whose nutrient intakes from food did not meet the EAR, as well as percentages by age and gender group. The risk of inadequacy was very low for 5 B vitamins (thiamin, riboflavin, niacin, vitamin B-6, and vitamin B-12) and for iron. For these nutrients, usual intakes were below the EAR for less than 3% of all the school-aged children. In contrast, the data suggest that risk of inadequacy
Calcium
A large majority of children had usual intakes of calcium that were less than 100% of the calcium AI (Table 3). The 75th percentile of the distribution of usual calcium intake was 101% of the AI. The distribution of calcium intakes as a percentage of the AI varied greatly by age and gender. Whereas less than 50% of children aged 6 to 8 years had calcium intakes below 100% of the AI, virtually all females aged 9 to 18 years had usual calcium intakes below 100% of their calcium AI. The 50th
Energy Intake
The full distribution of usual energy intake is shown in Table 4. For males in each age group, the 50th percentile of estimated usual energy intake was 97% of the REA. For females, it ranged from 84% of the REA for those aged 14 to 18 years to 88% for those aged 6 to 8 years. Only about 15% of females aged 6 to 8 years reached 100% of the REA, and about 25% of the older females did.
Differences by Demographic Group
In general, if the risk of inadequate intake was high among all children for a particular nutrient, the risk of inadequate intake was also high among each of the racial/ethnic groups (data not shown (12)). Non-Hispanic whites tended to have the lowest risk of inadequate intake, and “others” tended to have the highest risk. Differences by racial/ethnic group followed this pattern and were statistically significant (P=.01) for vitamin A, vitamin E (with non-Hispanic African-Americans along with
Discussion
This is the first study of children's dietary intake that assesses the adequacy of nutrient intake using data adjusted for day-to-day variation in intake and the recently released EARs. As has been clearly demonstrated by the National Research Council (13) and the Institute of Medicine (3), adjusting for day-to-day variation in intake may reduce error substantially when estimating the prevalence of intakes below a specified reference value.
Caution is indicated in interpreting these findings.
Applications
Using Dietary Reference Intake-based methods to assess the adequacy of nutrient intakes identifies a new set of nutrients—vitamin E, folate, phosphorus, and magnesium—that high percentages of children are consuming in amounts less than the current reference values. Our findings suggest that:
■ More attention should be given to improving intakes of those nutrients by school children of all ages;
■ Efforts are needed to increase intakes of calcium by a majority of children by age 9 years;
■ Females
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