Trends in childhood obesity in Japan: A nationwide observational study from 2012 to 2021

The persistent ascension of childhood obesity on a global scale constitutes a significant quandary. The prevalence of childhood obesity in Japan peaked in the early 2000s and has been reported to have declined since then, but recent data and its trend including the novel coronavirus disease 2019 (COVID-19) pandemic era are not available. Moreover, there is a dearth of studies examining the correlation between the trend in childhood obesity and exercise habits over the past decade. This study aims to examine the changes in the prevalence of obesity, physical fitness, and exercise habits over the past 10 years in Japanese children. We investigated the prevalence of childhood obesity in Japan, using the School Health Statistics Survey data from 2012 to 2021. The dataset has a sample size representative of children nationwide and includes variables for obesity, such as height, weight, and age. Data were classified into groups by sex and age (6-8, 9-11, and 12-14 years age). Children weighing 20% or more of the standard body weight are classified as obese. The annual percentage changes and average annual percentage changes were estimated using the joinpoint regression model. We also examined the trends in the physical fitness test score and exercise time. Average annual percentage changes of boys increased, especially in the 6- to 8-year age group (3.4%-4.6%). For girls, average annual percentage changes had increased in 6- to 8-year (2.5%-4.0%) and 9- to 11-year (0.9%-2.2%) age groups. Since the late 2010s, significantly increasing annual percentage changes were observed in 12- to 14-year age boys (6.7%-8.9%) and girls of many age groups (2.6%-8.6%). The physical fitness test score and exercise time showed decreasing trends since the late 2010s. Childhood obesity may have generally risen in Japan, in the last decade. Encouraging healthy eating and physical activity through school policies and curricula is necessary.