Patterns of Body Mass Trajectory among Japanese Children and Impacts of Life Style Factors during childhood

Introduction: Childhood overweight and obesity are global health problems. Understanding the variations in growth patterns, while considering body size in children, is essential to determine the optimal time for initiating interventions to control body size. In this study, we aimed to conduct an explorative analysis for identifying variations in the developmental patterns of body size and the impact of lifestyle factors in Japanese children.

Methods: The data included details of all 155 children (76 boys, 79 girls) born from April 2, 2005 to March 31, 2006 in Tsuru city, Japan. We used a discrete mixture model to explore the patterns of body mass index (BMI) trajectories. BMI was calculated as weight (kg)/height (m ²) and standardized using the z-score; it was measured at birth and then annually until the age of 9 years. We also used a multinomial logistic regression to identify factors associated with overweight in children.

Results: Five patterns of BMI trajectory were identified in both boys and girls. The three patterns associated with obesity or overweight in boys were being obese since the age of 5 years (4.0%), being overweight since the age of 5 years (20.0%), and gradually being overweight since the age of 7 years. The only pattern associated with overweight in girls was being overweight since the age of 4 years.

Conclusion: The results show that preschool age is a crucial period for becoming overweight in childhood; thus, intervention programs should target overweight preschoolers. Children who are not overweight but who show a gradual increase in their BMI during preschool should also be targeted by early intervention programs because they could become overweight after reaching school age. We also found that maternal working and children’s extracurricular activities were associated with overweight or obesity. However, the factors may differ by sex.