The effect of school on overweight in childhood: gain in body mass index during the school year and during summer vacation

Abstract

Objectives: To determine whether school or nonschool environments contribute more to childhood overweight, we compared children's gains in body mass index (BMI) when school is in session (during the kindergarten and first-grade school years) with their gains in BMI when school is out (during summer vacation).

Methods: The BMIs of 5380 children in 310 schools were measured as part of the Early Childhood Longitudinal Study, Kindergarten Cohort. We used these measurements to estimate BMI gain rates during kindergarten, summer, and first grade.

Results: Growth in BMI was typically faster and more variable during summer vacation than during the kindergarten and first-grade school years. The difference between school and summer gain rates was especially large for 3 at-risk subgroups: Black children, Hispanic children, and children who were already overweight at the beginning of kindergarten.

Conclusions: Although a school's diet and exercise policies may be less than ideal, it appears that early school environments contribute less to overweight than do nonschool environments.

FIGURE 1—

Expected body mass index (BMI) changes among children of average weight and among children who were overweight at the beginning of kindergarten: Early Childhood Longitudinal Study, Kindergarten Cohort, 1998–2000. Note. The threshold for overweight is the 95th percentile on the Centers for Disease Control and Prevention’s BMI-for-age charts, which show the BMI distributions that prevailed before recent increases in overweight. At the age of 5.5 years—the average age at the beginning of kindergarten—the 95th BMI percentiles are 18.1 for boys and 18.5 for girls; in the graph, these values are averaged to give an initial BMI of 18.3. The trajectories shown can be calculated with the estimates in Table 1 ▶ (calculations are available from the authors).

FIGURE 2—

Race/ethnicity-specific average body mass index (BMI) growth among children who were comparable on other variables: Early Childhood Longitudinal Study, Kindergarten Cohort, 1998–2000.