The nationwide school health checkup database enabled us to quantify trends in physical health among children from Grade 1 to Grade 9 and estimate the impact of the COVID-19 pandemic. The pandemic was associated with increased risks of being underweight, obesity, and poor visual acuity, whereas it was associated with decreased risks of dental caries and abnormal findings of urinalyses. The impacts of COVID-19 on some physical health measures (e.g., obesity, visual acuity) appeared to differ slightly between boys and girls.
The COVID-19 pandemic altered children’s daily lives,[4, 6] raising concerns about its impacts on their weight status. A systematic review published in 2022[24] indicated an increase in childhood obesity in many high-income countries during the pandemic. A notable example is the United States, where obesity in children aged 12–15 years increased by approximately 5%.[25] In Japan, two studies conducted in Osaka and Tokyo, along with their surrounding areas, have presented slightly differing views. A large-scale study in public schools in Osaka found a decrease in obesity among children aged 12–14 years, with almost no change in underweight status.[8] Conversely, a study targeting private schools in Tokyo and nearby areas reported an increase in BMI among boys and a decrease among girls.[9] Our study, aiming for a larger scale to improve generalizability, found that the impact of the COVID-19 pandemic on underweight was observed in both boys and girls in the 3rd year, while the impact on obesity was more pronounced in the earlier phase. As previously reported, the increase in obesity could be attributed to complex behavioral factors, such as decreased physical activity, prolonged sedentary time, changes in food behaviors, and alterations in the socioeconomic status of parents. The increase in eating disorders and underweight among children, with a majority of the patients being girls, have been reported from several studies, which might be linked to worsening mental health (e.g., social isolation, feeling of uncertainty) and economic factors affecting both children and parents.[7, 26–31] Importantly, our findings suggest that underweight is more prevalent in boys, who may not have as much access to healthcare as girls, highlighting a need for improvement in this area.
Our study revealed an elevated risk of poor visual acuity immediately following the COVID-19 pandemic, consistent with a previous study conducted in 11 schools in Japan.[19] In Japan, some studies indicate reduced outdoor physical activities and increased screen time,[6] both of which are well-known risk factors for myopia.[32, 33] Furthermore, we found that the impact on poor visual acuity is not limited to a single year, but persisted for 3 years among boys and 2 years among girls. In contrast, untreated dental caries decreased during the 3 years of the COVID-19 pandemic, which differs from previous studies. For instance, a study conducted in Tokyo reported an increase in dental caries in the 1st year of the pandemic.[10] This discrepancy may be due to variations in the target populations, but the exact mechanisms remain unclear.
A decrease in abnormal urinalysis results may be attributed to changes in infectious disease epidemiology among children, as these results often accompany normal transient findings or immune responses to non-specific infections.[34] During fiscal years 2020–2022, the Japanese government implemented infection prevention measures for students, such as mandatory mask-wearing, which were highly adhered to by students and teachers.(5) Consequently, the incidence rates of most infectious diseases (e.g., group A streptococcal pharyngitis) substantially reduced during this period.[35–38] Since the fiscal year 2023, infection prevention measures in schools have been relaxed, and then the incidence rates of most infectious diseases have returned to pre-pandemic levels or higher. Although addressing mild abnormalities in urinalyses often does not require medical intervention and may not be cost-effective,[39] ongoing monitoring can provide insights into the underlying health dynamics between pediatric infectious diseases and urinary tract functions.
The strength of our study lies in the use of nationwide datasets that cover various physical health outcomes, analyzed with recently developed robust statistical methods. However, our study has several limitations. Firstly, as the SHR database was primarily collected from public schools, the generalizability of our study findings to the entire pediatric population is uncertain despite our analyses being the largest of their kind. Secondly, the lack of demographic data, such as socioeconomic factors, lifestyle, and underlying diseases, precluded us from analyzing data with adjustment for important time-varying confounders, although our analyses with fixed-effect models implicitly accounted for time-fixed covariates. Thirdly, the SHR database does not provide information on geographic location due to the protection of personal information. Consequently, we could not analyze data to investigate the heterogeneity of the COVID-19 pandemic across different geographic locations. Fourthly, the health checkup records were collected for all students at the time of Grade 9. Due to this scheme, our DID analyses only estimated the impact of the COVID-19 pandemic among students in Grade 7–9. Long-term data or another data source would be required to investigate the impact of the pandemic on younger students.
In summary, our study highlighted essential changes in physical health among students in Japan, especially the increases in underweight, obesity, and poor visual acuity and the decreases in abnormal urinalysis findings during the COVID-19 pandemic. These findings underscore the multifaceted impact of the pandemic on children's health, revealing both direct and indirect effects on various health indicators, which could be valuable information for public health policy and pediatric healthcare planning in the post-pandemic era.