SANTA MONICA, Calif.—Nearly 40% of today’s kindergarteners have a body mass index (BMI) in the 75th percentile, and may be teetering on the edge of becoming overweight or obese, according to a new study published in the journal Pediatrics. The findings also suggest the proportion increases significantly during the elementary school years, with the largest gains between 1st and 3rd grades.
Researchers at the Rand Corporation analyzed data on nearly 6,000 Caucasian, black and Hispanic children who participated in the Early Childhood Longitudinal Study. Height and weight measurements were measured in children in kindergarten and 1st, 3rd, 5th, and 8th grades. The researchers estimated the proportions of children with BMI values in each quartile of the Centers for Disease Control and Prevention reference-population distribution according to gender and race/ethnicity. They conducted nonparametric tests of differences in BMI distributions over time within racial/ethnic groups and across racial/ethnic groups in each wave. Piecewise linear growth models were estimated to test for specific time periods during which the largest gains in BMI percentiles occurred.
Overall, nearly 40% of children started kindergarten with a BMI in the top quartile of the growth charts (BMI > 75th percentile). This proportion increased significantly during the elementary school years, and the largest gains were between 1st and 3rd grades (5.8 percentage points), but there was no further increase during middle school. Increases in BMI percentiles over time were most notable among Hispanic children and black girls.
