Impact of annual body mass index gain on obesity development in Japanese 6-year-old non-obese children

Background Effective timing of preventive intervention for adolescent obesity in non-obese school-aged children remains unclear. The aim of this study was to examine the impact of annual body mass index (BMI) gain on the development of adolescent obesity in 6-year-old non-obese Japanese children. Methods Longitudinal weight and height data were collected annually from 9723 children aged 6–14 years, and individual per-year BMI gains were calculated. The BMI ≥ the 95th percentile for each age and sex defined obesity. In 6-year-old non-obese children, logistic regression analyses were applied to correlate the annual BMI gain at each age with obesity at a final survey. Results The 6-year-old non-obese children who became obese at a final survey showed larger annual BMI gains at any age compared with their peers with respect to baseline BMI. Increases in annual BMI gain, even in early school age, raised the risk of adolescent obesity. Categorical analysis also showed that children aged 6–7 years with higher annual BMI gains than 1-SD above the mean had a significant risk for adolescent obesity (OR: 4.39 [95%CI: 2.98–6.46] in boys and 3.83 [95%CI: 2.60–5.63] in girls, respectively). Conclusions A larger annual BMI gain at any school age is a risk for adolescent obesity in 6-year-old non-obese children with no critical period. This suggests the need for earlier and continuous school-based surveillance using annual BMI gain for preventive intervention of adolescent obesity development.