Prevalence of overweight and influence of out-of-school seasonal periods on body mass index among American Indian schoolchildren.

Introduction: The prevalence of overweight and obesity among American Indian youth may be 2 to 3 times higher than the national average. Whether weight gain during discrete out-of-school periods is occurring and contributing to the prevalence of overweight and obesity in this population is unknown.

Methods: We obtained repeated cross-sectional body mass index (BMI) samples from third-, fourth-, fifth-, seventh-, and eighth-grade boys and girls who reside on the Wind River Indian Reservation in central Wyoming. We collected measures at the beginning of 2 school years (N = 251), during 2 holiday breaks (N = 226), and during 1 summer recess (N = 141). We determined prevalence of normal weight and overweight among participants by grade level, and we calculated paired comparisons of BMI, BMI z score, and weight status during the holiday breaks and summer recess.

Results: Combined prevalence of at risk for overweight and overweight was 62.0% for boys and 56.6% for girls. For fifth-grade girls, significant increases in BMI (P = .01) and z score (P < .001) occurred over the holiday break. BMI increased significantly over the summer among third- and fifth-grade girls and among fourth-grade boys, but changes in z scores were nonsignificant. We observed an increase in weight status by out-of-school time in BMI (P < .001) for schoolchildren at or above the 85th BMI percentile over the summer recess, but corresponding z scores did not change.

Conclusion: Prevalence of overweight among American Indian schoolchildren was higher than national estimates and higher than the prevalence in other similarly aged American Indian youth. Increases in BMI during out-of-school periods are likely due to normal growth, except among fifth-grade girls.