Changes in obesity and lifestyle behaviours during the COVID-19 pandemic in Chinese adolescents: A longitudinal analysis from 2019 to 2020

Background Since December 2019, the coronavirus disease 2019 (COVID-19) has become a global pandemic. Currently, the COVID-19 pandemic is still ongoing. What changes have taken place in the obesity and obesity-related lifestyle behaviours of adolescents during the first year of the COVID-19 pandemic? Objective This study aims at analysing the changes in obesity and lifestyle behaviours of Chinese adolescents before and 1 year after the outbreak of the COVID-19 pandemic, providing evidence for the global strategies to respond to the impact of the COVID-19 pandemic on adolescent obesity. Methods Physical examinations and student health and influencing factors questionnaires were conducted among 6047 adolescents aged 11-16 years by health professionals in Shanghai, China, before the COVID-19 pandemic (September-November of 2019) and 1 year after the outbreak of the COVID-19 pandemic (September-November of 2020). Paired chi 2 tests, paired t-tests or Wilcoxon signed-rank test was used to evaluate the changes in the obesity prevalence, BMI and lifestyle behaviours from 2019 to 2020. Results 1 year after the outbreak of the COVID-19 pandemic, the obesity prevalence of Chinese adolescents rose from 14.2% to 15.4% (p < 0.01), mainly because of the increase in boys. And the average BMI increased from 20.3 to 21.2 kg/m(2) (p < 0.01). Their lifestyle behaviours have also significantly changed. The mobile screen time increased from 0.25-1.50 h/day to 0.33-2.00 h/day (p < 0.01). The proportion of adolescents who participated in MVPA for >= 60 min/day on all 7 days during the past week dropped from 14.4% to 11.7% (p < 0.01). The generalized estimation equation analysis indicated that adolescents who participated in MVPA for >= 60 min/day on all 7 days had a lower likelihood of having obesity. Boys with computer time >= 2 h/day and girls with mobile screen time >= 2 h/day or TV time >= 2 h/day had a higher likelihood of having obesity. Conclusion This study found that 1 year after the outbreak of the COVID-19 pandemic, the BMI and obesity prevalence of Chinese adolescents increased and obesity-related lifestyle behaviours have also changed.