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Associations of social and demographic variables with calcium intakes of high school students

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Abstract

Objective To assess usual calcium intake of urban high school students and to assess the association of social and demographic variables with calcium intake.

Design A self-administered survey instrument containing the following elements: a food frequency questionnaire (FFQ) developed to estimate calcium intake; questions to elicit demographic information; and scales to reflect taste enjoyment of dairy products, social reinforcement for consumption of milk, perceptions of others' opinions about milk, and behavioral modeling of milk consumption (ie, the frequency of observing friends' and family members' use of milk). The FFQ was shown to include major sources of calcium in diets of a pretest sample (n=130).

Setting Urban high schools in a metropolitan setting.

Subjects/samples Students in one class per grade level in six high schools (approximately 900 students) were asked to participate. Of the 856 questionnaires completed, 785 were usable.

Main outcome measures Total calcium intake, as estimated using the FFQ.

Statistical analyses performed Descriptive statistics, t tests, one-way analysis of variance, correlation analysis, and stepwise multiple regression analysis were used to assess relationships of independent variables with calcium intake.

Results Mean estimated calcium intakes for male and female students were 1,146±41 mg/day (mean±standard error of the mean) and 815±26 mg/day (P<.001), respectively, 59% of which was obtained from milk. Median intakes were 1,016 mg/day for boys and 676 mg/day for girls, and more than half the students had intakes that were below current recommendations. Multiple regression analysis revealed significant predictors of total calcium intake: gender (boys>girls); taste enjoyment of dairy products; number of meals and snacks per day; age; ethnicity (whites>Asians); behavioral modeling of milk consumption; perceptions of others' opinions, recommendations, and use of milk; and soft drink consumption (total adjusted R2=.304). With the exception of age, these variables were positively associated with calcium intake. Regression equations developed for boys and girls separately revealed that different variables entered the equations.

Applications/conclusions Most of the variability in adolescents' calcium intakes remained unexplained by the variables included in this study. Nevertheless, the results suggest that education programs focusing on taste enjoyment of dairy products and building on the influence of peers and family members may have a positive impact on calcium intake.

Section snippets

Development of the Food Frequency Questionnaire

Because most existing food frequency questionnaires (FFQs) for estimation of calcium intake were developed for use with adult or elderly women 22., 23., 24., an FFQ was developed for this study. Two approaches were used to choose items for the FFQ: (a) selection of foods high in calcium from existing questionnaires and from food composition tables; and (b) identification of foods that are lower in calcium but that contribute substantially to calcium intake 25., 26.. Some foods that would

RESULTS

Of the 785 students included in the analysis, 338 were boys, 444 were girls, and 3 did not report gender. Descriptive data about the subjects are presented in Table 1. The three subjects who did not indicate gender were excluded from comparisons between boys and girls.

DISCUSSION

The major findings of this study were that the estimated calcium intake of many adolescents is lower than current recommendations, and that, although a number of social and demographic variables are associated with calcium intakes, much of the variability in intakes could not be explained. In interpreting these findings, it is important to address possible limitations of the data collection instrument. FFQs are generally acknowledged as useful in assessing usual dietary intakes of large numbers

APPLICATIONS

Although the variables investigated in this study left much of the variability in calcium intake unexplained, the results have several implications for action. The positive associations between taste enjoyment of dairy products and calcium intake should not be disregarded. Interventions emphasizing appeals to taste may be one means of influencing the calcium intake of adolescents. The positive impact of behavioral modeling of milk by friends and family, or of positive perceptions of family

Continuing education questionnaire for RDs

After reading the continuing education article, “Associations of social and demographic variables with calcium intakes of high school students,” please answer the following questions by indicating your responses on the continuing education questionnaire form located on the next page.

This activity has been approved for 1 hour of continuing education credit for registered dietitians by the Commission on Dietetic Registration. Answers to the continuing education questionnaire can be found on page

Acknowledgements

I thank the students for their participation, the school board and teachers for their assistance, Sara Paré, MSc, for her contributions to the pretesting phase, and the Dairy Bureau of Canada for financial support of this research.

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