Seasonal variability in weight change during elementary school.

Abstract

To examine seasonal variation in weight gain across elementary school (kindergarten-5th grade) among children who are healthy weight, overweight, or obese and from different racial and ethnic groups. The sample included 7,599 ethnically diverse students ages 5-7 years at baseline (Caucasian: 21.1%, Black: 36.2%, Hispanic: 26.0%, Asian 16.7%). Heights and weights were measured by school nurses at the beginning and end of each school year from kindergarten through the beginning of 5th grade. Beginning the summer after 1st grade, all children demonstrated a pattern of standardized BMI (zBMI) increases during the summer (0.04 to 0.09) and zBMI decreases across the school years (-0.06 to 0.00; P<0.0001). Hispanic children and children who were overweight and obese exhibited this pattern in kindergarten while children of other ethnicities and with a healthy weight did not (P<0.0001). Beginning the summer after 1st grade, a consistent pattern of relative weight gain during the summer months (Δ in BMI percentile=1.04) and weight loss during the school year (Δ in BMI percentile=-0.34) emerged. This pattern appeared earlier for children who were overweight, obese, or Hispanic. These findings suggest a need to better understand the causes of the problematic increases in weight during the summer.