Acceleration in BMI gain following COVID-19 restrictions. A longitudinal study with 7- to 10-year-old primary school children.

Background: The ramifications of COVID-19 restrictions might accelerate the already rising proportion of children with overweight or obesity.

Objectives: To assess the association between COVID-19 restrictions and changes in body mass index (BMI) and the proportion of children with overweight or obesity.

Methods: Cohort study with baseline measurements in September 2019 (prior to COVID-19 restrictions) and follow-up in June 2020, September 2020, and March 2021 at 12 primary schools in Austria. The height and weight of 738 children aged 7 to 10 years were measured and age- and sex-specific national and international standardized values were calculated. Changes over time were analysed by analysis of variance.

Results: Mean BMI standard deviation scores (SDS) increased by 0.24 (95% CI, 0.21-0.28) between September 2019 and March 2021. The proportion of children with overweight or obesity increased from 20.7% to 26.2% during this period (p < 0.001) using national reference values-EQUI BMI -comparable results were observed. Simultaneously, the height SDS increased by 0.06 (95% CI, 0.05-0.08) with a larger increase in girls (+0.11; p < 0.001) than in boys (+0.03; p = 0.19).

Conclusions: COVID-19 restrictions were associated with accelerated increases in mean BMI and the proportion of children with overweight or obesity. The increase in height SDS in girls calls for further investigations.