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Invited Commentary
August 26, 2021

Association of COVID-19 Mitigation Measures With Cardiorespiratory Fitness and Body Mass Index Among Children in Austria

Author Affiliations
  • 1Section of Epidemiology and Population Sciences, Department of Medicine, Baylor College of Medicine, Houston, Texas
  • 2Division of Cancer Prevention and Population Sciences, Department of Epidemiology, The University of Texas MD Anderson Cancer Center, Houston
JAMA Netw Open. 2021;4(8):e2121965. doi:10.1001/jamanetworkopen.2021.21965

The COVID-19 pandemic has been associated with unprecedented and rapid changes in the lives of children worldwide.1 Children have experienced marked disruptions in their daily lives owing to the COVID-19 pandemic and protective mitigation measures. Although COVID-19 in children is not as severe as it is in adults, the indirect consequences of the COVID-19 pandemic and mitigation measures have become a public health issue. Whether the COVID-19 pandemic will be associated with long-term physical and mental health is unknown. Several studies have described changes in children’s mental health, weight, eating habits, and physical activity associated with COVID-19 pandemic mitigation measures by using either self- or proxy-reported outcomes.2-4 Among these factors, an increase in sedentary behavior and a decrease in physical activity were associated with health-related parameters, such as cardiorespiratory fitness, which is related to long-term cardiovascular risk factors, and body mass index (BMI). However, most of these studies3,4 were cross-sectional and did not establish temporality because self- and proxy-reported outcomes are prone to recall bias. The association between COVID-19 mitigation measures and objectively measured cardiorespiratory fitness and BMI in children remains unclear. Jarnig et al5 performed a cohort study with a 1-year follow-up period from September 2019 to September 2020. Their study included a representative sample of 764 children aged 7 to 10 years from 12 primary schools. Cardiorespiratory fitness (6-minute endurance run test) and BMI were objectively measured to investigate the association of COVID-19 mitigation measures with these parameters. The COVID-19 mitigation measures were associated with a substantial reduction in cardiorespiratory fitness, increased BMI, and an increase in the proportion of children with overweight and obesity.

The study by Jarnig et al5 began as a randomized clinical trial that aimed to evaluate the effects of a physical education intervention on motor competence, cardiorespiratory fitness, and health among primary schoolchildren aged 7 to 10 years. However, because of the COVID-19 regulations, the intervention was stopped in March 2020. Therefore, the authors analyzed the data in a cohort study and evaluated the association of the COVID-19 mitigation measures with cardiorespiratory fitness and BMI among children. In this study, the 6-minute endurance run test was used to assess cardiorespiratory fitness. Jarnig et al5 collected both cardiorespiratory fitness and BMI at baseline in September and October 2019, BMI in May and June 2020, and both cardiorespiratory fitness and BMI in September and October 2020. The changes in cardiorespiratory fitness and BMI over time from September 2019 to September 2020 were estimated to reflect the consequences of the COVID-19 mitigation measures.

The data were analyzed using multilevel mixed models and 3-way analysis of variance with repeated measurements. There was a significant decrease in the mean (SD) distance that the children could run in 6 minutes from 917.0 (141.1) m in September 2019 and 815.0 (134.3) m in September 2020. Jarnig et al5 also observed a statistically significant increase in BMI during the follow-up period. The increase from September 2019 to June 2020 was greater than the increase from June 2020 to September 2020.

Moreover, the proportion of children with overweight or obesity increased by 1.8% in June 2020 and by 3.8% in September 2020 compared with September 2019. Results of a subgroup analysis stratified by sex and sports club membership and a sensitivity analysis using different overweight and obesity thresholds are also reported in detail. This study had several strengths. First, the study sample was representative of all primary schoolchildren in Austria because similar COVID-19 measures were implemented in all regions of Austria. Second, because the authors used longitudinal and objective parameters for cardiorespiratory fitness, height, and weight, the data may be more informative than those of previous studies2,3 that used self-reported data to assess the association of COVID-19 mitigation measures with health outcomes among children.

Jarnig et al5 noted a substantial reduction in cardiorespiratory fitness and an increase in BMI among children aged 7 to 10 years. Several factors should be considered when interpreting these results. First, there was no control group in this study because it was impossible to find a population of children not affected by the COVID-19 mitigation measures. Therefore, causal inferences could not me made. Second, because this study was not designed for analytic purposes, the authors did not collect data on several essential factors, such as social demographic characteristics (household income and parent educational level), lifestyle factors (diet and physical activity), sleep, and mental health (stress, anxiety, and depression levels), that may have been associated with changes in BMI or cardiorespiratory fitness. The increase in BMI among children may have been associated with disrupted or altered sleep schedules, nutritional level changes, lack of structured meal times, or lack of structured physical activity.6

The results of the study by Jarnig et al5 may be concerning with regard to whether the observed changes in cardiorespiratory fitness and BMI are transitory and whether recovery can occur after the removal of the COVID-19 mitigation measures. The long-term effects of the COVID-19 mitigation measures have not been investigated. This study highlighted important public health issues that governments, parents or legal guardians, and schools need to address to promote children’s well-being. A lower level of cardiorespiratory fitness could be directly associated with decreased physical activity, especially high-intensity activity, such as sports and exercises performed in physical education classes.7 Therefore, physical education classes should be improved to promote an active lifestyle among children. The physical development of children is as important as their academic development. The increase in BMI reflects various factors affected by the COVID-19 pandemic, such as changes in diet and mental health, decreased physical activity, and increased sedentary time. Additional actions are needed to improve the dietary quality and mental health status of children.

In summary, as reported in Jarnig et al,5 COVID-19 pandemic mitigation measures were associated with reduced cardiorespiratory fitness and increased BMI among children in Austria. Future studies should assess whether these changes in parameters are associated with an increased long-term risk of nontransmissible diseases related to obesity and lack of physical activity. More research is needed to understand the long-term effects of the COVID-19 mitigation measures on cardiorespiratory fitness and BMI as well as lifestyle behaviors and mental health. Governments, schools, and parents should be informed of this situation. Collaboration is needed to implement effective interventions related to diet and exercise to minimize the negative associations of the COVID-19 pandemic with the short- and long-term health of children.

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Article Information

Published: August 26, 2021. doi:10.1001/jamanetworkopen.2021.21965

Open Access: This is an open access article distributed under the terms of the CC-BY License. © 2021 Zhang X. JAMA Network Open.

Corresponding Author: Xiaotao Zhang, MD, PhD, Section of Epidemiology and Population Sciences, Department of Medicine, Baylor College of Medicine, One Baylor Plaza, MS: BCM307, Room 613D, Houston, TX 77030-3498 (Xiaotao.Zhang@bcm.edu).

Conflict of Interest Disclosures: None reported.

Funding/Support: Dr Zhang was supported by a research training grant RP160097 from the Cancer Prevention and Research Institute of Texas.

Role of the Funder/Sponsor: The funder had no role in the design and conduct of the study; collection, management, analysis, and interpretation of the data; preparation, review, or approval of the manuscript; and decision to submit the manuscript for publication.

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