Effect of COVID-19 Pandemic Lockdowns on Body Mass Index of Primary School Children from Different Socioeconomic Backgrounds

Background Childhood obesity is associated with various health outcomes. Restrictive measures to contain the spread of the Coronavirus Disease 2019 (COVID-19) pandemic, like lockdowns and school closures, affected children’s daily structure, physical activity, dietary habits, and sleep quality, possibly exacerbating risk factors for childhood obesity and higher body mass index (BMI) in children. Poor socioeconomic conditions may have led to relatively higher risk for elevated BMI levels following pandemic measures. In this study, the impact of measures related to the COVID-19 pandemic on the BMI of third graders was investigated regarding children’s socioeconomic background (SEB). Methods Data from 41,728 children (8.84 ± 0.56 years, 20,431 female) were collected in the context of a cohort study. Children were tested either before the pandemic (pre COVID : Sept2017–March2020, n = 26,314), or following the first (post LDI : Aug2020–Dec2020, n = 6657) or second lockdown in Germany (post LDII : Aug2021–Jan2022, n = 8757). SEB was based on the official school type classification of the state of Berlin. Outcome was BMI standard deviation scores (SDS). Results Significant effects of Time and SEB revealed elevated BMIs in post LDI ( M = 0.23, p = 0.011) and post LDII ( M = 0.22, p = 0.011) compared to pre COVID ( M = 0.17) cohorts and higher BMIs for children with lower SEB ( b = − 0.13 , p