Who is becoming overweight during the elementary school years?

Abstract

To determine the risk of becoming overweight for every first grader during the elementary school years and to determine whether the overall risk of becoming overweight for first graders is increasing. A descriptive study using school-based surveys of 12,588 boys and 12,264 girls who entered elementary school between 1989 and 1994. Six years later, the follow-up survey was conducted. Overweight was defined using the BMI percentile cut-off points. For every 5th percentile rank of first graders, the odds ratio for becoming overweight at seventh grade was calculated. A hockey stick regression analysis and the yearly trend of the risk for becoming overweight at 7th grade were also investigated. For overweight children in first grade, the odds ratio for staying at the same level was extremely high in both boys (35.0) and girls (63.9). The threshold effects of the BMI percentile value at first grade for becoming overweight were the 81st and 87th percentiles for boys and girls, respectively, according to the hockey stick model. The overall risk for becoming overweight significantly increased in boys during the study period (P=0.009). The present study determined the exact level of the risk for becoming overweight for every first grader at a different BMI percentile rank. The risk of overweight children in first grade who stayed at the same level at seventh grade was higher in girls than in boys. On the other hand, the trend of the entire population for becoming overweight presents only in boys. The different pattern of the trend of population for becoming overweight by sex during elementary school period may provide evidence to understand and predict overweight in adolescents and adults.