The Effect of the COVID-19 Pandemic on BMI in Children and Adolescents: A Retrospective Cohort Study

Background: The COVID-19 pandemic created circumstances with the potential to increase rates of overweight and obesity. We aimed to assess whether there were significant increases in BMI among a sample of children and adolescents during the year 2020compared to the two years prior to the pandemic. Methods: : For this retrospective cohort study, data was obtained from the electronic medical records of 8398 children 3-17 years of age who attended3 consecutive well visits between June 1 and October 31 in 2018, 2019 and 2020 in a single center in the Midwest. Generalized linear mixed models were used to calculate the differences in average BMI and obesityrates over the three years. Results: : Between 2019 and 2020, the mean BMI for the whole sample increased 3.2 percentile points (from the 70·5 th to the 73·7 th percentile; p<0·001)compared to an increase of 0.8 percentile point between 2018 and 2019 (p=0·008). The proportion of children and adolescents with obesity rose from 13% in 2019 to 15·2% in 2020 (p<0·001) compared to no significant increasefrom 2018 to 2019. Significant disparities in BMI were observed between socioeconomic and ethnic groups. Conclusions: Significant increases in BMI and obesity rates occurred in 2020 in this sample. We propose that the circumstances surrounding the COVID-19 pandemic contributed significantly to these increases.