COVID-19 Leads to Accelerated Increases in Children's BMI Z-Score Gain: An Interrupted Time Series Study

Introduction The coronavirus disease 2019 (COVID-19) pandemic may have negatively impacted children's weight status owing to the closure of schools, increased food insecurity and reliance on ultra-processed foods, and reduced opportunities for outdoor activity Methods In this interrupted time series study, height and weight were collected from children (n=1,770 children, mean age=8 7 years, 55 3% male, 64 6% Black) and transformed into BMI z-score (zBMI) each August/September from 2017 to 2020 Mixed effects linear regression estimated yearly zBMI change prior to the COVID-19 pandemic year (i e , 2017–2019) and during the COVID-19 pandemic year (i e , 2019–2020) Subgroup analyses by sex, race (i e , Black, White, other race), weight status (overweight or obese and normal weight), and grade (i e , lower = kindergarten–2nd grade and upper = 3rd–6th grade) were conducted Results Prior the COVID-19 pandemic, children's yearly zBMI change was +0 03 (95% CI= –0 10, 0 15) Change during the COVID-19 pandemic was +0 34 (95% CI=0 21, 0 47), an acceleration in zBMI change of +0 31 (95% CI=0 19, 0 44) For girls and boys, zBMI change accelerated by +0 33 (95% CI=0 16, 0 50) and +0 29 (95% CI=0 12, 0 46) during the pandemic year, respectively Acceleration in zBMI change was observed for children who were Black (+0 41, 95% CI=0 21, 0 61) and White (+0 22, 95% CI=0 06, 0 39) during the pandemic year For children classified as normal weight, zBMI change accelerated by +0 58 (95% CI=0 40, 0 76) Yearly zBMI change accelerated for lower elementary/primary (+0 23, 95% CI=0 08, 0 37) and upper elementary/primary children (+0 42, 95% CI=0 42, 0 63) Conclusions If similar zBMI accelerations occurred for children across the world, public health interventions to address this rapid unhealthy BMI gain will be urgently needed