Relationship between BMI-SDS trajectories and childhood asthma: a prospective cohort study from the Japan Environment and Children’s Study.

Background: The association between obesity and asthma in children has been reported. However, despite its clinical and public health significance, the relationship between longitudinal body mass index standard deviation score (BMI-SDS) trajectories in early life and development of childhood asthma in Japan remains to be elucidated. Methods: This study used fixed data on 11,433 parent-child pairs from the Japan Environment and Children’s Study, an ongoing national birth cohort study. Information on bronchial asthma was collected from the caregiver-reported questionnaire. The association between body mass index standard deviation score (BMI-SDS) trajectories during the first 3 years of life and the risk of bronchial asthma was examined using multivariate logistic regression analysis. Results: Children with sustained above-average growth had a higher risk of bronchial asthma at 3 years of age, compared with those with a normative BMI-SDS trajectory (adjusted odds ratio [aOR] 1.31, 95% confidence interval [CI] 1.11–1.55, p = 0.001). At 3 years of age, the association between a persistently high BMI-SDS trajectory and bronchial asthma was more pronounced in boys than in girls (boys: adjusted OR [aOR] 1.39, 95%CI 1.12–1.73, p = 0.003 vs. girls: aOR 1.24, 95%CI 0.96–1.61, p = 0.100). At 4 years of age, similar associations were observed, while the association was stronger in boys, it was significant in girls as well. Conclusion: The significance of this study is that it captures changes in BMI-SDS over time, rather than at a single point in time, our findings suggest that maintaining a normal BMI-SDS trajectory during childhood may be beneficial for asthma prevention.