Changes in Body Mass Index Z Score Over the Course of the Academic Year Among Children Attending Head Start

Abstract

We tested the hypothesis that among 3- to 5-year-old children attending Head Start, body mass index z score will decline during the academic year and increase during the summer. We used retrospective longitudinal growth data collected over 5 academic years from 1914 children (51% boys, 62% white) enrolled in a Michigan Head Start program. Changes in body mass index (BMI) z score, calculated as annual rate of change, during 2 academic years and the intervening summer were assessed by piecewise linear regression analysis. Potential covariates were gender, single-parent status, program year, race/ethnicity, age at initial enrollment, and family income (divided by household size). Mean BMI z score at the start of Head Start enrollment was 0.52 (95% confidence interval [95% CI] 0.39 to 0.65). Mean annual rates of BMI z score change were: -0.07 (95% CI -0.28 to 0.14) during the first year of enrollment, 0.62 (95% CI -0.0005 to 1.23) over the summer, and -0.82 (95% CI -1.50 to -0.13) during the second year of enrollment. The effect was most robust among girls of minority race/ethnicity. Head Start is associated with a shifting of BMI z scores toward the norm among low-income preschool-aged children, particularly among girls of minority race/ethnicity.