Impact of COVID-19 pandemic on children overweight in Japan in 2020.

Objective: This study aimed to explore the association between the coronavirus disease (COVID-19) pandemic and overweight incidence among preadolescent elementary school children in Japan.

Methods: A population-based longitudinal study was conducted in Adachi City, Tokyo, Japan, using data from the Adachi Child Health Impact of Living Difficulty (A-CHILD) study. The control group (2016-2018) comprised 434 children, and the COVID-19 exposure group (2018-2020) included 3500 children. Overweight was defined as a body mass index (BMI) z-score of 1 SD or more according to the World Health Organization standards. The study design involved comparing BMI z-scores before and after exposure to the pandemic, considering the associated lifestyle changes and potential consequences on physical activity, parental employment status and income.

Results: By 6th grade, the prevalence of overweight increased from 17.7% to 19.2% in the control group and 22.5% to 29.5% in the COVID-19 exposure group. Difference-in-differences analysis revealed that children's exposure to COVID-19 significantly increased BMI z-scores (coefficient 0.22, 95% confidence interval (CI) 0.14-0.29) and a higher odds ratio of overweight (odds ratio 2.51, 95% CI 1.12-5.62), even after adjusting for time-varying covariates.

Conclusions: The COVID-19 pandemic has been associated with an increased prevalence of overweight among elementary school children in Japan.