Association of COVID-19 Pandemic with Newly Diagnosed Anorexia Nervosa Among Children and Adolescents in Japan.

: The COVID-19 pandemic globally has negative effects on mental health. Research from Western countries, such as the US, Canada, Australia, and Europe, shows that the COVID-19 pandemic is associated with an increased trend of anorexia nervosa (AN) among children and adolescents. However, the trend after the pandemic in Eastern countries, including Japan, is not well-understood, and it remains unclear whether the pandemic is associated with the trend in these countries. This study aimed to examine the association between the COVID-19 pandemic and the newly diagnosed AN among children and adolescents in Japan. : Using the nationwide multi-hospital database in Japan, we analyzed the clinical outpatient data in the departments of pediatrics, psychosomatic medicine, and psychiatry. The participants comprised children and adolescents aged 7-19 years newly diagnosed with AN from January 2017 to January 2022. An interrupted time series analysis was used to compare the trends of newly diagnosed AN before and after the COVID-19 pandemic. Estimating the changes in the trends over the pandemic was performed using a Poisson regression model. : The total cases of newly diagnosed AN were 41 cases diagnosed in 38 months (1.08 cases per month) before the pandemic and 34 in 23 months (1.48 cases per month) after the pandemic. Notably, in the 7-14 age group, the cases per month increased from 0.74 to 1.13 cases per month over the period. Before the pandemic, a decrease in cases was observed (Incidence Rate Ratio [IRR] = 0.961; 95% CI = 0.932-0.990). Conversely, the after-pandemic period showed a contrasting trend, with increased cases (IRR = 1.096; 95% CI = 1.032-1.176). Furthermore, the number and cases per month in boys increased over the period, from 1 to 5 cases and from 0.03 to 0.22 cases per month, compared to girls from 28 to 26 cases and from 1.05 to 1.26 cases per month. Our findings suggest that sociocultural differences at a national level may not affect the trend of AN after the pandemic. The pandemic and lifestyle changes after the pandemic occurred in both Western and Eastern countries. Considering that, individual, parental, and peer factors related to the pandemic and the consequent lifestyle changes may be more associated with the development of AN. Further research in different countries is needed to elucidate the mechanisms of AN and the long-term impact of the pandemic.