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Scientific Reports
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10.1038/s41598-024-72461-5
Article
Bidirectional associations between sleep and anxiety among Chinese schoolchildren before and after the COVID-19 lockdown
Wang Zhuo 1
Hong Binxue 2
Su Ya 3
Li Minghui 4
Zou Kun 567
Wang Liang 8
Zhao Li 567
Jia Peng 910
Song Geyang songgy@scu.edu.cn

56
1 https://ror.org/05nda1d55 grid.419221.d 0000 0004 7648 0872 Department of Chronic and Non-Communicable Disease Control and Prevention, Sichuan Center for Disease Control and Prevention, Chengdu, China
2 https://ror.org/03hbkgr83 grid.507966.b Chengdu Center for Disease Control and Prevention, Chengdu, China
3 https://ror.org/00mkhxb43 grid.131063.6 0000 0001 2168 0066 Department of Sociology, University of Notre Dame, South Bend, USA
4 https://ror.org/05nda1d55 grid.419221.d 0000 0004 7648 0872 Department of Human Resources, Sichuan Center of Disease Control and Prevention, Chengdu, China
5 https://ror.org/011ashp19 grid.13291.38 0000 0001 0807 1581 Department of Health Policy and Management, West China School of Public Health and West China Fourth Hospital, Sichuan University, Chengdu, China
6 https://ror.org/011ashp19 grid.13291.38 0000 0001 0807 1581 Health Emergency Management Research Center, China-PUMC C.C. Chen Institute of Health, Sichuan University, Chengdu, China
7 https://ror.org/011ashp19 grid.13291.38 0000 0001 0807 1581 HEOA Group, West China School of Public Health and West China Fourth Hospital, Sichuan University, Chengdu, China
8 grid.259676.9 0000 0001 2214 9920 Department of Public Health, College of Health Professions, Marshall University, Huntingdon, USA
9 https://ror.org/033vjfk17 grid.49470.3e 0000 0001 2331 6153 School of Resources and Environmental Science, Wuhan University, Wuhan, China
10 https://ror.org/033vjfk17 grid.49470.3e 0000 0001 2331 6153 International Institute of Spatial Lifecourse Epidemiology (ISLE), Wuhan University, Wuhan, China
18 9 2024
18 9 2024
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6 9 2024
© The Author(s) 2024
2024
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The COVID-19 pandemic has critical implications for mental health in children. This study examined how the COVID-19 lockdown affected sleep duration and anxiety symptoms in Chinese school-aged children and the bidirectional association between sleep and anxiety before and during the COVID-19 lockdown. A school-based longitudinal cohort study was conducted to examine the relationship between sleep duration and anxiety scores before and after the COVID-19 lockdown from January to May 2020. Generalized estimating equations model was used to identify variables that contributed to the changes in sleep duration. The bidirectional relationship between sleep duration and anxiety symptoms was explored by cross-lagged analysis. 7681 children completed two waves of surveys were included in the analysis. The daily exercise duration, anxiety symptoms, and sleep duration decreased significantly during the lockdown compared with that before the lockdown. Based on generalized estimating equations model, older age, secondary school, and higher anxiety scores of participants were positively associated with sleep duration, while female and no COVID-19 infection history were negatively associated with it. Cross-lagged analysis showed higher anxiety score of children before the lockdown was significantly associated with shorter sleep duration during the lockdown; and shorter sleep duration of children before the lockdown was also significantly associated with a higher anxiety score during the lockdown. Under the context of the COVID-19 pandemic, there were longitudinal, bidirectional associations between children’s anxiety symptoms and sleep duration. For school students, mental health services and sleep education should be considered in the daily health education curriculum.

Keywords

Children
Sleep
Anxiety
Cohort
China
COVID-19
Subject terms

Health care
Risk factors
Psychology
Scientific Research Project of Sichuan Health CommitteeNo.20PJ122 Wang Zhuo http://dx.doi.org/10.13039/501100004377 Hong Kong Polytechnic University 19H0642 Zhao Li Science and Technology Department of Sichuan Province, China2020JDKP0021 Zhao Li issue-copyright-statement© Springer Nature Limited 2024
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pmcIntroduction

With the increase of school problems, academic pressure, psychosocial difficulties, and other influencing factors, the mental health state of school-aged children may have deteriorated1. Studies reported that the COVID-19 pandemic also made children and adolescents more vulnerable and the proportion of students who experienced psychological problems had increased2. From the psychological and social perspective, some direct and indirect impacts of the pandemic might significantly affect the mental health of children and adolescents now and in the future3,4. During or after the pandemic, children and adolescents were more likely to experience anxiety, depression, sleep and appetite disorders, and social disorders3,5,6.

Anxiety disorder is one of the most frequently occurring mental disorders worldwide7. Epidemiological studies found that approximately 5–20% of children and adolescents were diagnosed with anxiety disorder8–10. Anxiety is closely related to perceived stress, and the school closures during the COVID-19 pandemic brought about significant changes to students’ daily lives and might affect students’ perceived stress11. Adequate sleep is crucial for the health development of children and adolescents. Healthy sleep contributes to physical health, immune function, psychological well-being, and can actively support cognitive function in children and adolescents12,13. Sleep comprises many dimensions, including sleep continuity, sleep efficiency, and sleep duration14. While these aspects all have been proved to be closely related to children and adolescents’ development, sleep duration has been explored more in mental health and can be used as a predictor for children’s behavior problems and mental disorders, including anxiety15,16. Besides the direct relationship between sleep duration and anxiety symptoms, studies have proved that exercise duration, which might have also changed during the COVID-19, can affect both of them17,18.

Current literatures have provided important clue of the bidirectional association between anxiety and sleep. Existing research has underscored that children and adolescents with anxiety symptoms frequently suffer from insufficient sleep, while insufficient sleep could further instigate or exacerbate anxiety7,19,20. However, few studies have researched their bidirectional relationship using longitudinal data with a large sample size. Moreover, since the COVID-19 pandemic have been an international public health emergency, the daily life and study of children around the world have been disturbed seriously. School-aged children may experience school closure, isolation, increased family pressure, changed exercise duration, and reduced peer communication, all of which may be potential factors of sleep insufficiency and anxiety21,22. However, longitudinal studies under the context of the COVID-19 pandemic were rare.

With reference to the above research gaps, the present study attempted to examine the bidirectional associations between sleep and anxiety before and after COVID-19 lockdown. Based on the Chengdu Children’s Positive Development (CPCD) cohort study, our study aimed to explore three issues:1. Did the COVID-19 lockdown affect the sleep of primary and secondary school students?

2. Did the COVID-19 lockdown affect anxiety among primary and secondary school students?

3. Was there a bidirectional relationship between sleep and anxiety before and after COVID-19 lockdown?

Methods

Participants and procedure

The Chengdu Positive Child Development (CPCD) study was a school-based cohort, in which five primary and secondary schools (grade one to grade nine) from central and suburb Chengdu, Sichuan province, western China were randomly selected. All students of the five schools participated in this cohort and two waves of survey have been carried out. The first-wave survey was conducted from December 23, 2019, to January 13, 2020, before the outbreak of COVID-19 and the lockdown of cities. The second wave survey was performed, from June 16, 2020, to July 8, 2020, after the resumption of primary and secondary schools in Chengdu. The participating schools, children, and their parents all provided written informed consent before participating in this study. More information about CPCD study has been reported previously23,24. The CPCD study received ethical approval from the Sichuan University (K2020025).

Measures of key variables

Sleep duration

Two questions were used to evaluate children and adolescents’ sleep duration. Participants were asked “the average daily sleep duration of three months before COVID-19 (before January 2020)” and “the average daily sleep duration during COVID-19 (from January 2020 to May 2020 before returning to school)”. The daily sleeping time was converted into minutes for analysis.

Anxiety symptom

Screen for child anxiety related emotional disorders (SCARED), a tool based on child and parent self-reporting, was used to measure anxiety symptoms of children25–27. It is a 41-item version for anxiety-related symptoms experienced recently, including panic/somatic, generalized anxiety, separation anxiety, social phobia, school phobia, and social phobia, each item is scored on a three-point Likert scale of 0 to 2, with 0 indicating ‘not at all’ and 2 indicating ‘often’. The maximum score of SCARED is 82, with the higher score indicating worse anxiety symptoms. It has been reported that satisfactory reliability and validity of SCARED are satisfactory in the Chinese population28. In this study, the Cronbach’s α for SCARED was 0.945 in the first wave and 0.954 in the second wave.

Demographics and COVID-19 infection history

The participants’ demographic information included age (years), gender (boy or girl), ethnicity (Han Chinese or Minorities), grade (primary school or secondary school), residence (urban or rural), number of children (only child or more than one), COVID-19 exposure (Did you or your family members get infected by COVID-19? yes or no), and exercise duration before and during the COVID-19 lockdown.

Statistical analysis

The number of students with missing data is limited and the data is missing completely at random (MCAR). Therefore, we conducted a complete case analysis, excluding participants with missing data. Descriptive statistics, including mean with standard deviation (SD) and total number with percentage ratio, were conducted to summarize the students’ social-demographic variables. The differences of variables by genders were tested by χ2 tests for categorical variables or t-tests for continuous variables. Paired samples t-test was adopted to compare exercise duration (minutes), anxiety scores, and sleep duration (minutes) before and after the lockdown. Generalized estimating equations model (GEE, the R Package “Geepack”) was used to examine variables associated with changes in sleep duration, which was set as an exchangeable working correlation matrix, linear regression, and main effect model. A traditional cross-lagged analysis (the R Package “lavaan”) was used to preliminary explore the bidirectional relationships between sleep duration and anxiety symptoms. This model did not always include covariates, because the main goal was to control the influence of autocorrelation29,30. The p-value of less than 0.05 was considered statistically significant. Data analysis used R version 4.1.2 (2021-11-01).

Results

Participants’ characteristics

7900 children (average age 10.60 years) completed the first wave survey before the COVID-19 outbreak, in which 51.65% were boys, 99.19% were Han, 68.10% were primary school students, 64.08% lived in the urban area, and 34.46% were from only-child families. During the COVID-19, 7742 children completed the second wave survey, and 255 participating students (3.29%) reported COVID-19 infection history (Table 1). Table 1 Demographics of participants in Chengdu Survey of Positive Child Development.

Characteristics	N (%) or Mean ± SD	p-value (sex)	
All	Boys	Girls	
Age (year) (wave 1)	10.60 ± 2.19	10.60 ± 2.19	10.60 ± 2.18	0.90	
Gender (wave 1)	
 Boy	4080 (51.65)	–	–		
 Girl	3820 (48.35)	–	–		
Ethnicity (wave 1)	
 Han	7836 (99.19)	4045 (99.14)	3791 (99.24)	0.72	
 Minorities	64 (0.81)	35 (0.86)	29 (0.76)	
Grade (wave 1)	
 Primary school	5380 (68.10)	2822 (69.17)	2558 (66.96)	0.04*	
 Secondary school	2520 (31.90)	1258 (30.83)	1262 (33.04)	
Residence (wave 1)	
 Urban	5058 (64.03)	2642 (64.77)	2416 (63.35)	0.20	
 Rural	2842 (35.97)	1437 (35.23)	1398 (36.65)	
Number of children (wave 1)	
 Only child	2722 (34.46)	1490 (36.52)	1232 (32.25)	 < 0.01**	
 More than one	5178 (65.54)	2590 (63.48)	2588 (67.75)	
COVID-19 exposure (wave 2)	
 Yes	255 (3.29)	133 (3.34)	122 (3.24)	0.86	
 No	7487(96.71)	3848 (96.66)	3639 (96.76)	
The differences of age, ethnicity, grade, residence, number of children, and wave 2 COVID-19 exposure were tested between genders (boy and girl) based on χ2 tests for categorical variables or t-tests for continuous variables.

SD standard deviation.

*p < 0.05.

**p < 0.01.

Finally, a total of 7681 participating students were included in the final analysis of the GEE and Cross-lagged model.

Changes in exercise duration, anxiety symptoms, and sleep duration before and during the COVID-19 lockdown

Table 2 presented the changes of the children’s exercise duration, anxiety symptoms, and sleep duration before (wave 1) and during (wave 2) the COVID-19 lockdown. Compared with pre-lockdown levels, there was a significant decrease in exercise duration, anxiety symptoms, and sleep duration during the COVID-19 lockdown. Specifically, exercise duration decreased from 114.71 (SD = 116.35) min to 105.23 (SD = 110.61) min, anxiety symptoms scores decreased from 17.09 (SD = 14.75) to 15.25 (SD = 15.08), and sleep duration decreased from 546.59 (SD = 75.64) min to 527.39 (SD = 87.59) min (p < 0.001). Table 2 Changes in exercise duration, anxiety symptoms and sleep duration before and during the COVID-19 lockdown.

Variables	Wave 1	Wave 2	P	
Mean	SD	Mean	SD	
Exercise duration (minutes)	114.71	116.35	105.23	110.61	 < 0.01**	
Anxiety scores	17.09	14.75	15.25	15.08	 < 0.01**	
Sleeping duration (minutes)	546.59	75.64	527.39	87.59	 < 0.01**	
Exercise duration, anxiety scores and sleep duration of wave 1 and wave 2 were compared by paired samples t-test.

SD standard deviation.

*p < 0.05.

**p < 0.01.

Variables associated with change of sleep duration based on generalized estimating equations

Compared with sleep duration before the epidemic, 3525 participants (45.89%) had shorter sleep duration, 2214 (28.82%) maintained their sleep duration, and 1942 (25.28%) experienced longer sleep duration during the COVID-19 lockdown. Table 3 showed the variables that might be related to the alteration of sleep duration using the GEE model. Participants’ older age (β =  − 2.58, p < 0.01), secondary school (β =  − 36.49, p < 0.01), and higher anxiety scores (β =  − 0.13, p < 0.01) were risk variables which might contribute to decreased sleep duration. Female (β = 4.00, p < 0.01), No COVID-19 infection history (β = 24.35, p < 0.01) was the potential protective factor of sleep duration. Table 3 Variables associated with the alteration of sleep duration based on generalized estimating equations (N = 7681).

Variables	β	SE	Wald χ2	p	
Age (year)	 − 2.58	0.53	23.85	 < 0.01**	
Gender = female	4.00	1.53	6.85	 < 0.01**	
Ethnicity = minorities	3.93	8.70	0.20	0.65	
Grade = secondary school	 − 36.49	2.33	245.48	 < 0.01**	
Residence = rural	 − 0.02	0.01	2.11	0.15	
Number of children = more than one	 − 1.17	1.60	0.53	0.47	
Wave 2 COVID-19 exposure = no	24.35	5.91	16.98	 < 0.01**	
Exercise duration (minutes)	0.01	0.01	0.85	0.36	
Anxiety scores	 − 0.13	0.05	7.15	 < 0.01**	
SD standard error.

*p < 0.05.

**p < 0.01.

Longitudinal bidirectional correlation between sleep duration and anxiety symptoms

Our cross-lagged model was a saturated model. The chi-square value, degree of freedom and root mean square error of approximation (RMSEA) were 0, and comparative fit index (CFI), incremental fit index (IFI), Tucker–Lewis index (TLI), and goodness of fit index were 1. Higher anxiety score at wave 1 was significantly associated with shorter sleep duration at wave 2 (β =  − 0.07, p < 0.001). Shorter sleep duration at wave 1 was also significantly associated with higher anxiety scores at wave 2 (β =  − 0.05, P < 0.001). The cross-lagged model showed that children with higher anxiety scores were prone to have shorter sleep duration both before and during the COVID-19 lockdown (β =  − 0.03, p < 0.01; β =  − 0.04, p < 0.001). Similarly, children with shorter sleep duration were more likely to have higher anxiety scores both before and during the COVID-19 lockdown. Anxiety scores at wave 1 were positively related to the anxiety scores at wave 2 (β = 0.52, p < 0.001), and previous sleep duration was also positively related to sleep duration during the COVID-19 lockdown (β = 0.50, p < 0.001) (Fig. 1).Fig. 1 Cross-lagged model between sleep duration and anxiety scores. Anxiety Wave1: anxiety scores before the COVID-19 lockdown; Anxiety Wave2: anxiety scores during the COVID-19 lockdown; Sleep Wave1: sleep duration before the COVID-19 lockdown; Sleep Wave2: sleep duration during the COVID-19 lockdown. The two-way arrow indicates the result of correlation analysis; the one-way arrow indicates the result of path analysis; the correlation coefficient and regression coefficient are standardized estimations. *p < 0.05; **p < 0.01; ***p < 0.001.

Discussion

The COVID-19 outbreak has profound impacts on the mental health and well-being of people around the world. At the beginning of the epidemic, to minimize the possibility of disease transmission, China’s Ministry of Education launched a national delayed school opening in January 202031. Although the preventive measures were necessary, isolation affected the physical and mental health of children and adolescents32,33. Children and adolescents were already in a sensitive period for escalating problems with sleep and anxiety20,34,35. Our study provided a theoretical contribution to the relationship between mental health and sleep of children under the context of the COVID-19 pandemic, and would help healthcare professionals and policymakers to make targeted intervention strategies for children who had sleep and psychological problems during pandemic.

Our study showed that children's sleep and exercise duration during the COVID-19 lockdown were significantly shorter, while their anxiety scores were lower than that before the COVID-19 lockdown. Our findings are not entirely consistent with previous studies. For exercise duration, our finding is consistent with a review including 15 records in 11 countries36. For sleep duration, a review figured out an increased sleep duration for children during the COVID-19 because of late bedtimes and later waketimes37. However, in many research, nearly half of participants could not meet the recommendation still38. For children and adolescents’ anxiety symptoms, a review summarized that anxiety symptoms increased slightly during COVID-1939. For example, an online survey of Spain, Italy, and Portugal showed that children in different parts of Europe had different levels of anxiety symptoms during the epidemic. And children in Spain and Italy showed higher anxiety scores, while Portuguese children seem to be more adapted to the pandemic32. Reasons for different research findings might be the different isolation measures, cultural background, family relations, personal behavior, personal emotional ability, etc40,41. Students in our study might receive more emotional support from families or friends, and their emotional competence showed improvement during COVID-19, which could help to reduce the anxiety symptoms40,42,43. In addition, Chinese children and adolescents studied at home before school opening, which might reduce their academic pressure and difficult interpersonal relationships at school44,45.

Our results of the GEE model suggested that ethnicity, residence, number of children, and exercise duration were not significant predictors of sleep duration, while older age, male, higher grades, COVID-19 infection history, and higher anxiety scores were associated with decreased sleep duration.

The cross-lagged model showed students with shorter sleep duration before the COVID-19 lockdown were more likely to obtain higher anxiety scores during the COVID-19 lockdown, while students who had higher anxiety scores before the COVID-19 lockdown had shorter sleep duration during the COVID-19 lockdown. The bidirectional effect of anxiety and sleep obtained in this study further enriched the existing research. At present, with the recommended sleep duration for children and adolescents being 9–11 h per night46,47, many studies found that inadequate sleep could lead to the increase of mental problems such as anxiety. There were relatively few reports on whether and how anxiety influences sleep duration on various functional areas. Recent reports have shown that people respond differently to lack of sleep. For example, evidence of concurrent and longitudinal association between sleep difficulties and anxiety was found in some community and clinical sample studies of young people20. Some studies have also found that different gender might have different response to sleep duration and anxiety symptoms48. Studies have shown that anxiety could shorten sleep duration, and the influence of anxiety on sleep duration was different among individuals49. In addition to the evidence of population prevalence, there is also molecular evidence to illustrate the bidirectional relationship between anxiety and sleep. For example, it was found that several transmitters such as norepinephrine, acetylcholine, GABA, dopamine, glutamate, serotonin, and adenosine have effects on sleep–wake regulation and anxiety50–53.

Inadequate sleep is a recognized cause of increased anxiety, but there were few studies, especially longitudinal studies, on the bidirectional relationship between sleep and anxiety. Our findings highlighted the impact of COVID-19 exposure on anxiety and sleep among Chinese children, and explored the bidirectional relationship between anxiety and sleep. Our results are convincing, with a large sample size of 7681 and longitudinal cohort study design. The study had several limitations. First, although cluster random sampling was used, this study was only carried out in Chengdu, Sichuan Province, which may affect its representativeness. More participants from different regions should be included in the future. Secondly, sleep duration was self-reported rather than objectively measured, the accuracy of the data may be affected. Future research should incorporate objective measurements to enhance the accuracy and reliability of the data. Thirdly, although this was a longitudinal study, clear causal associations between sleep and anxiety under the context of COVID-19 may be difficult to draw from an observational study. Some other confounding factors should be considered, such as study pressure, school relationships, social support. In the next step, there will be more waves of surveys to further verify the results of this study.

Conclusions

The COVID-19 pandemic has a negative influence on children’s sleep duration and anxiety symptoms. Under the context of the COVID-19 pandemic, there was longitudinal, bidirectional correlation between children’s anxiety symptoms and sleep duration. Incorporating mental health services and sleep education into the daily health education curriculum for school students may be necessary to reduce the psychological, physical, and social impact of students in any possible public emergency in the future.

Acknowledgements

The longitudinal project and the preparation of this paper are financially supported by Prof. Daniel T. L. Shek’s research project at The Hong Kong Polytechnic University. We thank the International Institute of Spatial Lifecourse Epidemiology (ISLE) for research support.

Author contributions

GS is the principle investigator and data custodian of the Sichuan Positive Youth Development Study. Data analysis was performed by ZW, BH, YS, ML, KZ, LW, PJ and GS. The first draft of the manuscript was prepared by ZW, BH and GS, revised by YS, ML, KZ, LW, LZ and PJ. All authors approved the final draft of the manuscript and agreed to be accountable for all aspects of the work in ensuring that questions related to the accuracy or integrity of any part of the work are appropriately investigated and resolved.

Funding

This work was supported by the Hong Kong Polytechnic University (Longitudinal study of positive youth development 19H0642), Science and Technology Department of Sichuan Province, China (2020JDKP0021), Scientific Research Project of Sichuan Health Committee (No.20PJ122).

Data availability

The raw data generated and analyzed in this study are not publically available due to the appropriate protection of the personal protection of children and adolescents, but are available from the corresponding author on a reasonable request.

Competing interests

The authors declare no competing interests.

Ethics approval and consent to participate

All the experiment protocol for involving humans data was in accordance to guidelines of national/international/institutional or Declaration of Helsinki. The study protocol was approved by the Ethics Committee of Sichuan University (K2020025). All participants provided written informed consent before participating in the survey.

Publisher's note

Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.

These authors contributed equally: Zhuo Wang and Binxue Hong.
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