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Nonrestorative sleep and its associated factors in Chinese adolescents and the moderation effects of coffee or tea consumption

BMC Public Health volume 24, Article number: 2398 (2024) Cite this article

Abstract

Background

Nonrestorative sleep (NRS) is related to numerous adverse outcomes. There is rare evidence of its associated factors, especially in Chinese adolescents. This study aimed to explore the factors associated with NRS in Chinese adolescents and the potential moderation effects of coffee or tea consumption.

Methods

This cross-sectional study invited adolescents attending Grades 7–11 in Nanjing, China, to complete a self-administered questionnaire, including their NRS, stress, anxiety, physical symptoms, depression, sociodemographics, and lifestyles. Linear regressions were applied to investigate the associated factors of their NRS, with the moderation effects of coffee or tea consumption and other characteristics being tested by additionally including their interactions.

Results

Totally 481 adolescents (49% male, age 15.5 ± 1.5 years) were enrolled, with the average global NRS score of 42.16 ± 7.57. Higher family income (β = 2.01, P = 0.007), longer sleep duration (β = 2.33, P = 0.011), and moderate after-class activity (β = 1.50, P = 0.044) contributed less NRS, while higher educational level (β = −2.60, P = 0.033), more coffee or tea consumption (β = −1.68, P = 0.013), physical symptoms (β = −3.85, P < 0.001), stress (β = −0.23, P = 0.005), anxiety (β = −1.54, P = 0.045), and depression (β = −0.13, P = 0.014) contributed more NRS. Females (β = 0.82, P = 0.005), older age (β = −0.46, P = 0.029), and higher education level (β = −1.68, P < 0.001) contributed less refreshment from sleep, more physical/medical symptoms of NRS, and less daytime function, respectively. Coffee or tea consumption moderated the associations of somatic symptoms (β = 0.25, P = 0.021), stress (β = 0.29, P = 0.022), anxiety (β = 0.27, P = 0.005), and depression (β = 0.17, P = 0.021) with NRS.

Conclusions

Longer sleep duration, moderate after-class activity, reduced coffee or tea consumption, and promotion of physical and mental health may help reduce adolescents’ NRS. Coffee or tea consumption may help buffer the negative associations of somatic symptoms, stress, anxiety, and depression with NRS.

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Background

Sleep is essential for the growth and cognitive and psychological development of adolescents. During adolescence, all individuals undergo physical, psychological, cognitive, and behavioral changes to complete the transition from childhood to adulthood [1]. In this process, adolescents were found to be vulnerable to sleep disorders, such as insomnia [2]. Nonrestorative sleep (NRS), which refers to feeling unrefreshed after normal sleep duration [3], used to be one of the primary symptoms of insomnia but is now independently listed as “other specified insomnia disorder” in the Diagnostic and Statistical Manual of Mental Disorders, fifth edition (DSM-V) [4]. NRS has gained more academic attention during the last two decades. In a representative study in the United States, 43.0% of the enrolled adolescents “often did not really feel rested” and 17.7% “had this feeling every day” which was even more common than symptoms of insomnia, such as difficulty initiating sleep [5].

Chinese adolescents are also suffering from NRS. Among the few studies on NRS in Chinese adolescents, one representative study found that Hong Kong Chinese adolescents only scored 4.8 out of 0–10 in NRS (10 being the highest), and 47.5% of them reported feeling unrefreshed upon awakening [6]. Another one showed that 17.9% of mainland Chinese adolescents had daytime sleepiness [7]. It is noteworthy that the persistence and partial remission of NRS were 31.9% and 22.7%, respectively, which indicates that NRS can be a problem throughout the whole lifespan [8]. More NRS were found to be associated with lower quality of life, emotional problems, hyperactivity/inattention, and suicide ideation in adolescents [6], as well as a higher risk of accidents during work and leisure time, lower general psychological well-being, impaired quality of life, and more existence of chronic problems in adults [8,9,10,11]. Hence, investigating adolescents’ NRS and identifying the associated factors from an early stage deserves more attention to promote early interventions.

According to the social-ecological model of sleep health, the “upstream” of sleep should include elements from the individual, social, and societal levels [12]. The reported factors associated with NRS in adults include sociodemographics, environment, lifestyle, and physical and psychological factors. Age was one of the most studied sociodemographic factors, but inconsistent results were yielded. Some studies showed that younger adults reported more NRS, and the prevalence decreased with age [13], whereas middle-aged adults were found to have more NRS than the younger or older groups in other studies [14]. Females were more vulnerable to NRS than males, and marital status, country, ethnicity, work, and education level were demonstrated to be linked with NRS [13,14,15]. Concerning environmental factors, the risk of NRS would increase if sleeping in a bedroom that is stuffy and uncomfortable [14]. Consistent evidence was found regarding the associations of NRS with physical and psychological health. Overall, people with physical and psychological health issues reported greater NRS. For example, the likelihood increased when people had chronic fatigue syndrome [16]. People who had anxiety disorders, depressive disorders, and experienced stressful events were also more prone to have higher levels of NRS [14]. However, these studies only focused on adult populations, and the knowledge of NRS in adolescents, especially in Chinese adolescents, remains inadequate. Moreover, many previous studies explored the associated factors without taking stress and physical and mental health as covariates and used unstandardized instruments and insufficient adjustment, which might reduce the reliability of the evidence.

The effects of caffeine on sleep and health should not be neglected. As the most popular psychoactive substance worldwide, caffeine is commonly used to reduce sleepiness, which is one manifestation of NRS. Some research proposed that caffeine has more practical advantages than ensuring adequate restorative sleep because of convenient access [17]. However, evidence also suggests that caffeine contributes to poor sleep. In a recent review, the majority of experimental studies indicated that caffeine consumption negatively affected sleep latency, sleep duration, sleep efficiency, and the relative time spent in deep sleep [18]. Moreover, some researchers investigated the impact of coffee consumption timing on its outcomes. The results showed that evening caffeine use moderates the association between caffeine consumption and subjective sleep quality among students [19]. Therefore, whether caffeine brings a restorative feeling of sleep and whether it differs in different age groups would be interesting when investigating NRS.

To conclude, there remains a dearth of understanding about NRS and the associated factors in Chinese adolescents. Adolescents have less control over the environment and unique lifestyles compared with adults [20]. For example, adolescents need to obey the school regulations and rest schedules in schools [21]. They also need to do homework in the evening, which objectively affects their sleep duration, timing, or even the chronotype [22]. When encountering sleep problems, adolescents were less likely to seek professional healthcare compared with adults [20]. Therefore, based on the social-ecological model of sleep health and previous evidence on adults, this study aimed to explore the factors associated with NRS and the potential moderation effects in Chinese adolescents, so as to identify vulnerable groups and modifiable factors and to reduce NRS in adolescents.

Methods

Participants

Adolescents who were attending Grades 7 to 11 (age range: 13–18 years old) and were able to read simplified Chinese were eligible. Those who were taking drugs for sleep problems or had mental illnesses were excluded. Totally 490 students were approached. Of which, 486 (99.2%) students consented to participate, and their parents or legal guardians gave written consent. After excluding five students with no valid answers on NRSS, 481 (98.2%) students were finally included in the final data analysis. According to the usual rule of thumb of 10 subjects per factor for linear regression, the sample size is adequate for the analysis in this article with 15 independent variables [23].

Procedures

This study took the form of a school-based cross-sectional survey through convenient sampling from May 31 to June 21, 2019, in Nanjing, China. Before the survey started, the questionnaires were sent to the investigated schools to see whether the questions were suitable or sensitive to adolescents, and approval was obtained from the schools and teachers. The leaders of the schools randomly selected the classes. For high school, one liberal arts class and one science class in each grade were chosen at random. All the students in the selected classes were invited. At the first school visit, the trained investigators introduced the study procedures and questionnaires, and an information sheet outlining the study procedures was distributed to each student who was willing to participate and passed on to their parents/guardians. The students were invited to complete the questionnaires by themselves once they and their parents/guardians gave the written informed consent. The adolescents were asked to voluntarily fill in the questions by themselves based on their actual feelings, with the emphasis on no standard answer for each question. Only questions like family income could be answered with the help of parents or legal guardians. Lastly, all participants were free to skip any survey questions in case of uncomfortable feelings or concerns.

Ethics approval of this study has been obtained from the Institutional Review Board of the University of Hong Kong/Hospital Authority Hong Kong West Cluster (Ref no.: UW19-165).

Measures

Nonrestorative sleep scale (NRSS)

The Nonrestorative Sleep Scale (NRSS) has four subscales—refreshment from sleep, physical/medical symptoms of NRS, daytime functioning, and affective symptoms [24]. The Chinese NRSS replicated the factor structure as the English version [24]. A total of 12 items yield a global score of 12–60, with a higher global and subscale score indicating a lower level of NRS [24]. The Chinese NRSS had internal reliability (Cronbach’s alpha) and test-retest reliability of 0.83 and 0.86, respectively [24].

Reduced morningness eveningness questionnaire (rMEQ)

The Chinese version of the reduced Morningness Eveningness Questionnaire is a self-rated questionnaire comprising five items (items 1, 7, 10, 18, and 19 of the original version of MEQ) to evaluate circadian rhythm and sleep rhythm patterns [25]. The sum of the scores on each item was converted into three categories: evening type (4–11), neutral type (12–17), and morning type (18–25) [25]. The rMEQ showed satisfied reliability with Cronbach’s alpha of 0.70 [25].

Perceived stress scale (PSS)

We assessed the perceived stress level of adolescents using the 10-item Chinese version of the Perceived Stress Scale. Each item was self-graded on a 0–4 scale, with a higher score indicating a higher level of perceived stress [26]. The Cronbach’s alpha of the Chinese PSS was 0.86 in Chinese policewomen [26].

Symptom checklist 90 (SCL-90)-somatization subscale

The somatization subscale is a 12-item scale measuring somatic symptoms under the SCL-90. The items employed a 0–4 Likert scale from “never” to “serious”. The internal consistency of the somatization subscale was satisfied (Cronbach’s alpha: 0.88) [27].

Symptom checklist 90 (SCL-90)-anxiety subscale

Adolescents self-rated their anxiety using the anxiety subscale of the SCL-90, which comprises ten items. All the items were rated from 0 (“never”) to 4 (“serious”). The anxiety subscale had an internal consistency (Cronbach’s alpha) of 0.88 [27].

Center for epidemiologic studies depression (CES-D)

The CES-D is a popular instrument for evaluating the severity of depression. Each item was graded on a 0–3 scale, resulting in a global score between 0 and 60, with higher scores implying more severe symptoms. The Cronbach’s alpha of the Chinese CES-D in the Chinese undergraduate sample was 0.895 [28].

Sociodemographic and lifestyle characteristics

Adolescents were also asked to report their date of birth (DD/MM/YY), gender (Male; Female), grade (Middle school: Grade 7–9; High school: Grade 10–11), and family income (Chinese Yuan, CNY: < CNY5000; ≥ CNY5000) (CNY 7.24 = USD 1). Lifestyle characteristics, including physical exercise habits (≥ 3 times/week; < 3 times/week), duration of after-class activity (< 30 min/day; 30–60 min/day; ≥ 60 min/day), sleep duration (< 8 h/day; ≥ 8 h/day), smoking (Never or quitted; Yes), alcohol consumption (Never or quitted; Yes), and coffee or tea consumption (Never or quitted; Yes), were also asked.

Statistical analysis

All data were entered and cleaned by cross-checking with the originally collected paper questionnaires. In terms of the description of the population’s characteristics, categorical variables were depicted through frequencies and percentages, continuous data of normal distribution were summarized using means and standard deviations (SD), whereas non-normally distributed data were described using medians and interquartile ranges (IQR). Body Mass Index (BMI) was calculated by the individual’s weight in kilograms divided by the square of height in meters. Linear regressions were employed to estimate the unadjusted βs and adjusted βs of the associations of NRS with all other variables with mutual adjustments. The moderation effects of coffee or tea were tested with interaction terms that were additionally included in the linear regressions. The model adequacy was assessed by studentized residuals, and the absence of multicollinearity was verified by the variance inflation factor (VIF) with the Package “car” [29]. We set the significance level as 5% for all statistical tests, with all estimates accompanied by 95% confidence intervals (95% CIs) where appropriate. All data analysis was conducted with R version 4.3.2.

Results

Description of the enrolled adolescents

A total of 490 students were approached, and 481 (49% male) returned the questionnaires validly. The students had an average age of 15.5 years (SD: 1.5, Range: 13–18). The average global score of the NRSS was 42.16 (SD: 7.57) (Table 1).

Table 1 Summary of sociodemographics, lifestyles, and scales for the adolescents
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Factors associated with global NRS

Table 2 shows that higher family income (β = 2.01, P = 0.007), longer sleep duration (β = 2.33, P = 0.011), and moderate after-class activity (β = 1.50, P = 0.044) contributed less NRS, while higher educational level (β = −2.60, P = 0.033), more coffee or tea consumption (β = −1.68, P = 0.013), physical symptoms (β = −0.32, P < 0.001), stress (β = −0.23, P = 0.005), anxiety (β = −0.15, P = 0.045), and depression (β = −0.13, P = 0.014) were associated with more NRS after adjustment. The VIF values ranged from 1.03 to 2.01.

Table 2 Associated factors of NRSS in Chinese adolescents
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Associated factors of each dimension of NRS

Table 3 shows that depression (β = −0.06, P = 0.015) was negatively associated with refreshment from sleep; females (β = 0.82, P = 0.005) showed worse refreshment from sleep than males, while longer sleep duration (β = 1.84, P < 0.001) contributed less refreshment from sleep; an increase of age (β = −0.46, P = 0.029) and somatic symptoms (β = −0.02, P < 0.001) were associated with worse physical/medical symptoms of NRS; education level (β = −1.68, P < 0.001), family income (β = 0.96, P = 0.002), sleep duration (β = 1.08, P = 0.004), moderate after-class activity (β = 0.84, P = 0.006), and depression (β = −0.05, P = 0.023) were associated with daytime function; somatic symptoms (β = −0.07, P = 0.008) and stress (β = −0.09, P < 0.001) were negatively related to affective symptoms. VIF values for the four regression models ranged from 1.03 to 2.01.

Table 3 Factors associated with each dimension of NRSS
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Moderation effect of coffee or tea consumption

Table 4 shows that the moderation effects of significant sociodemographic and lifestyle characteristics were tested, and the results showed that coffee or tea consumption significantly moderated the effect of somatic symptoms (β = 0.25, P < 0.001), stress (β = 0.29, P < 0.001), anxiety (β = 0.27, P < 0.001) and depression (β = 0.17, P < 0.001).

Table 4 The moderation effects of coffee or tea consumption
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Figure 1 shows the statistically significant interaction effects of coffee or tea consumption (all P ≤ 0.022). Specifically, coffee or tea consumption may reduce the associations of higher somatic symptoms, stress, anxiety, and depression with NRS.

Fig. 1
figure 1

The moderation effects of coffee or tea consumption on NRS

NRSS: Nonrestorative sleep scale, SCL-90-S: Symptom Checklist 90 (SCL-90)-Somatization subscale, PSS: Perceived Stress Scale, SCL-90-A: Symptom Checklist 90 (SCL-90)-Anxiety subscale, CSED: Center for Epidemiologic Studies Depression

Full size image

Discussion

This was the first study that investigated the factors associated with NRS among Chinese adolescents. Higher family income, longer sleep duration, and moderate after-class activity contributed less NRS, while higher educational level, more coffee or tea consumption, physical symptoms, stress, anxiety, and depression were associated with more NRS. The moderation effects of coffee or tea consumption first showed that it may reduce the negative associations of somatic symptoms, stress, anxiety, and depression with NRS.

High school students showed more NRS than middle school students. One previous study found that more years of schooling was associated with a higher risk of NRS after adjustment [14]. Occupation or job classification impacts NRS in adults, and the study resembles jobs for adolescents since adolescents need to attend classes and complete assignments [30]. High school students usually need to sustain more academic pressures than middle school students in China. Therefore, they may have less time to sleep but a higher stress level, leading to greater NRS.

Higher family income predicted less NRS in this study. Students with higher family incomes might have less economic stress, which could reduce the overall pressure to some extent [31]. They may also have a higher probability of being provided better sleep conditions, such as a better bedroom environment and a comfortable bed, which could induce a smaller likelihood of NRS [14]. However, such environmental factors were not covered in this study due to the rating difficulty for adolescents. Future studies should consider those environmental and ecological factors to identify whether a better environment could help relieve NRS.

Adolescents who sleep longer than 8 h per day suffer less from NRS compared to those with shorter sleep duration. Although our previous study showed that continuous sleep duration was not associated with NRS in Chinese adults [32], another study found that adequate sleep duration was a protective factor for NRS in Japanese adults [33]. Eight to ten hours of sleep duration is recommended for teenagers to obtain optimal health [34]. The effects of sleep duration might be related to adequate slow-wave sleep (SWS), which is considered to be the most restorative sleep stage [35]. Therefore, the association between sleep duration and NRS may not be linear, and future studies should explore the specific sleep duration classifications for different populations to identify the recommended sleep duration. This study suggests that an adequate sleep duration for adolescents is recommended to prevent or relieve NRS.

Moderate after-class activity was associated with less NRS. After-class activity could relieve stress and strengthen individual resilience to stress, thereby decreasing NRS [36]. Adolescents in this study have the freedom to choose after-class activities between classes and after school from their schools, such as sports and music. Participation in such activities has been linked to several positive outcomes, such as more supporting relationships, better personal skills, and decreased severity of attention-deficit/hyperactivity disorder [37]. However, although moderate after-class activity may reduce NRS, the association was insignificant if the duration was more prolonged. A longer after-class activity duration might occupy their study time and shorten the original sleep duration that they could obtain. Moreover, students engaging in prolonged after-class activities may result in less study time and thus increased stress, which counteracted the social supporting effects on sleep [38].

Consumption of coffee or tea was associated with worse NRS. Caffeine in coffee or tea can lead to sleep deprivation. Studies showed that coffee intake was negatively associated with adolescents’ sleep duration and quality [39], while an insignificant association was reported in Hong Kong Chinese adults when coffee or tea was investigated separately [32]. Moreover, compared with adolescents, adults may suffer from more sources of pressure that can impact their sleep, which makes caffeine intake less critical in its impacts on sleep [40]. The inconsistent results may also result from the distinguished lifestyles of Hong Kong Chinese adults and mainland Chinese adolescents. For adults, drinking coffee or tea may be part of their everyday lifestyles or to benefit their health in addition to refreshing [41], while adolescents consume drinks with caffeine for short sleep duration or to maintain daytime awareness. However, drinking milk tea has become a new lifestyle in China during the last few years. Future studies should identify different types of caffeine intake when assessing their associations with sleep.

The significant associations of NRS with somatic symptoms, stress, anxiety, and depression were in line with our previous study on Chinese adults [32]. People with more somatic symptoms were more prone to be disturbed during sleep, consequently leading to a higher likelihood of NRS [42]. Furthermore, somatic symptoms, anxiety, and depression were related to the general stress model, in which stressors could increase the activity of the hypothalamic-pituitary-adrenal axis and release cortisol while decreasing melatonin, thus impacting the restorative function of sleep [43].

Most of the factors associated with each dimension of NRS were similar to those of the global NRS score. Female adolescents showed worse refreshment from sleep than male students, which aligns with previous studies that reported that the NRS of females was worse than that of males [14]. Females usually reported worse sleep conditions than males, which might be attributed to various biological, psychological, and sociocultural factors [44]. For example, the decreased homeostatic sleep drive and delayed circadian phase influenced by puberty may contribute to the development of insomnia and a mismatch with social schedules [45]. Moreover, the female adolescents reported a longer ideal sleep duration, which may make them give a worse subjective sleep rating than males with similar sleep duration [46]. Age was negatively associated with physical/medical symptoms of NRS, and adolescents in high school showed poorer daytime function than middle school adolescents, which means physical/medical symptoms of NRS and daytime function get worse when they get older or turn into a higher grade. The physical/medical symptoms of NRS include physical sensations or unusual feelings, headaches, body pain, heart racing, etc., which are related to stress [47]. Adolescents of older age usually have higher grades and experience more academic stress in China, which induces more impairment of NRS [32].

Notably, we first found the moderation effects of coffee or tea consumption. Compared with their peers, adolescents with coffee or tea consumption reported less NRS when their somatic symptoms, stress, anxiety, and depression increased. In other words, coffee or tea consumption showed protective effects on NRS when adolescents have more somatic symptoms, stress, anxiety, and depression. Caffeine has been reported to reduce pain, anxiety, and depression [48, 49]. Caffeine is a constituent of many prescription drugs for pain because of its vasoconstricting and anti-inflammatory effects. Habitual caffeine consumption could lead to a higher pain threshold and higher heat pain tolerance, which may lower the adverse effects of somatic symptoms on NRS [49]. Moreover, caffeine consumption was significantly associated with decreased risks of mental problems. Despite the lack of a consensus on the underlying mechanism, researchers proposed that coffee provides significant amounts of various acids, which could show anti-inflammatory and antioxidant effects that may contribute to the pathophysiology of anxiety and depression [48]. Also, caffeine is a nonspecific adenosine A1/A2A receptor antagonist, and its major metabolites can act on adenosine receptors in the brain, which may lower the risk of depression [48]. However, the consumption dose and timing may be related to its protective effects. Therefore, future studies, especially intervention studies, should explore more detailed information on coffee or tea consumption when evaluating its health effects, such as their timing, dose, and separate effects.

Our findings highlight the importance of adequate sleep duration and after-class activity to restorative sleep. For policymakers and educators, delaying the school start time and reducing the burden of homework could be helpful to ensure adolescents’ restorative sleep [50]. Although excess caffeine products such as coffee or tea are not commonly suggested for adolescents, if adolescents are suffering from high levels of psychosocial problems, such as stress, anxiety, or depression, coffee or tea might alleviate their negative effects on restorative sleep.

Several study limitations were still worth noting. First, all the measures were self-reported in this study; objective measurements such as actigraphy or some other devices might help give more convincing evidence, especially on the associations between physiological sleep parameters and NRS. Moreover, objective indicators of NRS would be desirable in the future. Second, some other popular lifestyles, such as screen time and milk tea, were not considered in this study and could be tested in the future. Third, covariates such as environmental factors and other health conditions were not examined. Lastly, longitudinal studies would be of significance in revealing the causal relationships between potential associated factors and NRS, which helps find possible interventions to prevent adolescents’ NRS in the future. However, this study employed the standardized instrument for measuring adolescents’ NRS, which should be more precise than adopting only one single question to measure NRS. Moreover, the power of the estimates, especially those of the sociodemographics and lifestyles, was more robust with the adjustment of somatic symptoms, stress, anxiety, and depression, which were reported to be highly associated with NRS.

Conclusion

To conclude, longer sleep duration, moderate after-class activity, reduced coffee or tea consumption, and the promotion of physical and mental health may help reduce adolescents’ NRS. Coffee or tea consumption may reduce the negative associations of somatic symptoms, stress, anxiety, and depression with NRS.

Data availability

The datasets generated and/or analyzed during the current study are not publicly available due to confidentiality.

Abbreviations

BMI:

Body mass index

CNY:

Chinese Yuan

CES-D:

Center for Epidemiologic Studies Depression

IQR:

Interquartile ranges

NRS:

Nonrestorative sleep

NRSS:

Nonrestorative Sleep Scale

PSS:

Perceived Stress Scale

rMEQ:

Reduced Morningness Eveningness Questionnaire

SCL-90:

Symptom Checklist 90

SCL-90-S:

Symptom Checklist 90 (SCL-90)-Somatization subscale

SCL-90-A:

Symptom Checklist 90 (SCL-90)-Anxiety subscale

SD:

Standard deviations

VIF:

Variance inflation factor

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Funding

This study was supported by the National Natural Science Foundation of China [Grant No. 72204117], People’s Republic of China, the Shenzhen Stability Support Program in Colleges and Universities of China [Grant No. 20220810202707001], the Project of Philosophy and Social Science of Guangdong Province [Grant No. GD23YSH10], and the Start-up Fund for Scientific Research of Young Teachers in Shenzhen University [Grant No. 000002112408].

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Authors and Affiliations

  1. School of Nursing, Nanjing Medical University, 101 Longmian Avenue, Nanjing, Jiangsu, 211166, China

    Sha Li, Yan Zhe Wang & Zheng Lin

  2. School of Nursing, Li Ka Shing Faculty of Medicine, The University of Hong Kong, 3 Sassoon Road, Pokfulam, Hong Kong SAR, 999077, China

    Daniel Yee Tak Fong & Xing Chen Shang

  3. School of Nursing & School of Public Health, Yangzhou University, 136 Jiangyang Middle Road, Yangzhou, Jiangsu, 225009, China

    Xing Chen Shang

  4. South China Hospital, Medical School, Shenzhen University, 1 Fuxin Road, Shenzhen, Guangdong, 518111, China

    Wei Jie Gong

  5. Department of Family Medicine, Medical School, Shenzhen University, 1066 Xueyuan Road, Shenzhen, Guangdong, 518055, China

    Wei Jie Gong

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  1. Sha Li
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  3. Yan Zhe Wang
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  4. Zheng Lin
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Contributions

SL involved in the data collection, analyzed and interpreted the data, drafted and revised the manuscript. DYTF, XCS, and WJG revised the manuscript critically for important intellectual content. SL, DYTF and ZL contributed to the conception and design of the study. YZW prepared the material. SL and WJG acquired the funding. All authors made important contributions to the revision of the manuscript. All authors read and approved the final manuscript.

Corresponding authors

Correspondence to Xing Chen Shang or Wei Jie Gong.

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Li, S., Fong, D.Y.T., Wang, Y.Z. et al. Nonrestorative sleep and its associated factors in Chinese adolescents and the moderation effects of coffee or tea consumption. BMC Public Health 24, 2398 (2024). https://doi.org/10.1186/s12889-024-19936-2

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BMC Public Health

ISSN: 1471-2458

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