Association of Overall Screen Time and Outdoor Activity with Emotional and Behavioral Health Problems

Background Psychological problems among children and adolescents have become a public health issue. This study aimed to investigate associations between screen time (ST), outdoor activity (OA), and emotional and behavioral health problems (EBHPs) among South Chinese children and adolescents. Methods A total of 30,188 boys and girls from 14 elementary and junior high schools on six streets in Shenzhen were included in this study. EBHPs were measured with the strengths and diculties questionnaire; OA and ST data were obtained through self-reporting. Descriptive analyses, chi-square tests, and logistic regressions were performed using SPSS 23.0. In our study, 42.4% students had insucient OA, 24.2% students had excessive ST, the abnormal prevalence of emotional symptoms, conduct problems, peer problems, hyperactivity problems, prosocial behavior, and total diculties scales were 18.5%, 6.9%, 6.4%, 13.1%, 10.7% and 8.8%. There were signicant associations between ST/OA, independent and addictive interaction, and EBHPs among children and adolescents. Participants with high exposure to ST were more likely to have EBHPs than those with low exposure; participants with low exposure to OA were also more likely to have EBHPs than those with high exposure. The interactive associations of ST and OA on EBHPs were stronger than those of ST or OA individually. Our results show positive associations between ST, OA, and EBHPs. They indicate that interventions should be considered for decreasing ST and increasing OA in children and adolescents. protective factors and strongly implies a need to identify strategies to reduce this public health problem. Our study explores factors affecting EBHPs from the perspective of ST and OA, providing a theoretical basis for solving public health problems on children and adolescents. Our study has the primary strength of having a large sample size. We distributed this survey through 6 streets and 14 schools, including elementary, junior high, and senior high schools. We also analysed several potential confounders. In this study, we adopted the interactive effect to explore the correlation between ST and OA and EBHPs, further demonstrating that we should pay close attention to those factors inuencing the mental health of children and adolescents.

ST, and EBHPs among Chinese children and adolescents in order to provide a better theoretical basis for explaining EBHPs through the interaction of ST and OA.

Study sample
The questionnaire on the growth trajectory and health index of primary and secondary school students was a prospective survey representing physical and psychological problems of contemporary children and adolescents. Ultimately, 14 schools were selected in Shenzhen, Bao'an district. In total, 33,801 children and adolescents in grades 1-12 were withdrawn as those that did not meet the requirements or had incomplete data were removed, so that 30,188 children and adolescents were selected. The age range was 6 to 18 years. Written informed consent and questionnaires were obtained from the students or their parents. There were two types of questionnaires: one for parents (grades 1-4) and one for self-reporting (grades [5][6][7][8][9][10][11][12]. This study was approved by the Ethics Committee of Anhui Medical University.

Screen time
The ST of participants was determined with two questions. One question was, "How much time do you / your child spend watching TV, using computers, and playing with cell phones or other electric devices on an average weekday?" The other was, "How much time do you /your child spend watching TV, using computers, and playing with cell phones or other electric devices on an average weekend day?" The overall average ST was calculated according to previous methods [37]. ST was categorized as ≥2 h/day (high) or 2 h/days (low) [38].

Outdoor activity
The OA option had two questions, which were, "On an average weekday (Monday to Friday) during the past month, how much time did you usually spend time on outdoor activity?" and "On an average weekend day (Saturday or Sunday) during the past month, how much time did you usually spend time on outdoor activity?" Minutes spent outdoors per week were computed as [(5*outdoor time on weekdays) + (2*outdoor time on weekend days)], to convert this estimate to hours per day, we divided the estimate by 420 (60 min * 7 days per week) [26]. OA was categorized as 1 h/day and ≥1 h/day [26].

Emotional and behavioral health problems
Participants self-reported using the strengths and di culties questionnaire (SDQ) [39]. The 25 items of the SDQ are used to measure strengths and di culties on ve scales (emotional symptoms, conduct problems, hyperactivity problems, peer problems, and prosocial behavior). Each scale contains ve items scored from 0 to 2, giving a scale range of 0 to 10. The score for total di culties is the sum of four scales (prosocial behavior is excluded). Higher scores re ect greater di culty (excluding prosocial behavior). SDQ scores (including total di culties, prosocial behavior, emotional symptoms, conduct problems, hyperactivity problems, and peer problems) were categorized as normal, borderline, or abnormal. Total SDQ scores above the 90th percentile were classi ed as abnormal; those in the 80th to 90th percentile range were 'borderline,' and those below the 80th percentile were 'normal' [40]. Children's responses were categorized as normal, borderline, or abnormal for each subscale.

Covariates
In this analysis, demographic information was included as covariates, such as sex, family economic level, parental education, academic record, and homeplace. Family economic level was classi ed as below moderate, moderate, or above moderate. Parental education level was classi ed as junior high or below, senior high, or junior college and above. Academic record was classi ed as below moderate, moderate, or above moderate. Homeplace was classi ed as country, city, or town.

Statistical analyses
Statistical analyses were performed with SPSS 23.0. Descriptive analyses were used to show demographic information of the sample. Pearson's chi-squared tests were performed to test the prevalence of EBHPs. Andersson Excel was used to calculate the interaction data of the additive interaction model [41].
Multivariable logistic regression was used to explore the independent and interactive associations of ST and OA. A p < 0.05 was considered signi cant.

Study on emotional and behavioral health problems and additive interaction model between outdoor activity and screen time
In Fig. 1 In emotional and behavioral health problems and the additive interaction model between OA and ST, our results have shown that low OA and high ST are positively correlated with emotional symptoms, hyperactivity problems, peer problems, prosocial behaviors, and total di culties. High OA and low ST were negatively related to emotional symptoms, hyperactivity problems, peer problems, prosocial behaviors, and total di culties.

Discussion
This study investigated the associations between ST and OA and EBHPs in Chinese children and adolescents. After adjusting for confounding factors, ST and OA were found to have independent and additive interaction effects on EBHPs. There were gender differences in the distribution of EBHPs. Boys were more likely than girls to report conduct problems, hyperactivity problems, peer problems, and prosocial behavior. This result supports conclusions of previous studies [42][43][44][45]. Results were similar to other studies showing girls are more likely to have higher emotional symptoms [46,47].
With progress in science and technology, the use of electronic products and mobile phones has increased signi cantly. Some studies have proposed that more than half of students have high ST (>2 h/d) [48]. One study found that watching television, videos, or DVDs for three hours or more daily is associated with a small increase in conduct problems between ages 5 and 7 [22]. According to an American study, computer ST was correlated with SDQ scores [49]. Studies of younger-aged children demonstrated that higher ST is a risk factor for EBHPs [50]. Other studies have found a correlation between emotional or behavioral di culties and spending more time on computers [51][52][53], as well as increased di culty in disengaging from the computer [54]. This also re ects the in uence of electronic devices on interpersonal communication. High ST can cause various maladaptive psychophysiological responses, such as arousal of the central nervous system, and can also adversely affect sleep patterns [55]. Adolescents with psychosocial di culties may choose to use ST as a form of self-release.
Another study explained the relationships between inactivity, ST, and psychosocial di culties as bidirectional [56]. In addition, children who suffered from neurodevelopmental disorders had more di culties disengaging from screen devices, which could exacerbate emotional/behavioral di culties [57]. Similarly, our ndings support the conclusion that high ST has adverse effects on the EBHPs of children and adolescents [58].
Our OA ndings are consistent with other PA and OA studies [3,26, 59-60,]. The mechanism between PA and EBHPs attributed to PA may improve monoamines (norepinephrine and serotonin) by increasing neurotransmitter activity and increasing or moderately activating the limbic system and decreasing cortisol levels [61], indicating that PA can improve mental health outcomes for all children, in a similar way, PA and OA are supplement each other, adolescents who spending more time outside is associated with higher physical activity levels, which in turn increase the probability of improvement mental health [26]. OA can encourage opportunities for school connectedness and intra-and interpersonal development for young people, highlight the importance of fostering school connectedness and interpersonal communication in supporting healthy adolescent development [48,[62][63], lower isolation and loneliness [64], and increase con dence and social skills [65,66] to improve students' mental health. The special effect of outdoor activity has also been reported with some studies that be associated with positive mood and mental well-beings [62]. Beyond these, outdoor activity is also used as therapy, which is associated with decreased symptoms of ADHD [67]. Moreover, the effect of outdoor activity which is not only limited to the psychological status of the normal population, but also plays an important regulating role in diabetes patients [68]. Furthermore, compared with physical activity indoors, exercising in outdoor environments was associated with greater feelings of emotion and positive engagement, decreases in negative emotion and depression, and adverse psychological mood; one possible reason is participants reported greater enjoyment and satisfaction with outdoor activity and declared a greater intent to repeat the activity at a later date [69]. Therefore, it is imperative to promote outdoor activities for children and adolescents.
We found a remarkable additive interaction between high ST and OA on EBHPs. The additive interaction model analysis demonstrates that the combination of low OA and high ST are positively associated with concurrent total di culties when compared with high PA and low ST after controlling for other confounders. In addition, high ST and insu cient OA interact to increase psychological problems. Also, in comparison with high OA and low ST, low OA and low ST and low OA and high ST were correlated with some scales. Some possible reasons were that high ST may displace their study and OA time, then further infect their physical and psychosocial health [70][71][72]. Meanwhile, each additional hour spent outdoors per day was associated with 7.0 more minutes of moderate-to-vigorous physical activity, 762 more steps, and 13 fewer minutes of sedentary time [29]. Extended exposure to screens limits opportunities for personal connectedness, problem-solving, and self-development, and promotes isolation, which can increase adolescents' vulnerability to adverse mental health outcomes [73]. Previous research demonstrates the interactive effects of insu cient PA and high ST on psychological di culties in children and adolescents [32, [74][75][76]. But there is no study about outdoor activity and screen time on mental health among children and adolescents. Adolescents in Dhaka City who had high recreational ST and were not meeting PA recommendations were more likely to suffer psychosocial di culties [2]. The frequency of emotional and behavioral health problems and the potential long-term consequences make it an important research topic in relation to risk and protective factors and strongly implies a need to identify strategies to reduce this public health problem. Our study explores factors affecting EBHPs from the perspective of ST and OA, providing a theoretical basis for solving public health problems on children and adolescents.
Our study has the primary strength of having a large sample size. We distributed this survey through 6 streets and 14 schools, including elementary, junior high, and senior high schools. We also analysed several potential confounders. In this study, we adopted the interactive effect to explore the correlation between ST and OA and EBHPs, further demonstrating that we should pay close attention to those factors in uencing the mental health of children and adolescents.
This research also has several limitations. First, this study is cross-sectional and could not determine causality or direction. Second, ST and OA were acquired through self-reporting, which may introduce a recall bias. Our further research has utilized objective measures such as accelerometers to assess OA and ST.
Third, we could not obtain answers from absent students. Poor mood and behavioral health problem status may be more prevalent among frequently or longterm absent students. Therefore, the prevalence of mood health problems detected in this study is likely underestimated.

Conclusion
In this study, our results con rmed that high exposure to ST and OA increase the risk of EBHPs among Chinese children and adolescents. Overall, time spent outdoors was consistently associated with improved physical behaviors (i.e., more physical activity and less sedentary behavior) and tness outcomes when The study was approved by the Ethics Committee of Anhui Medical University. All focus group participants provided signed informed consent prior to the start of the focus groups/.

Consent for publication
Not Applicable.

Availability of data and materials
The datasets that were generated analyzed for the current study are not publicly available as the author does not have permission to share the data.

Competing interests
The authors declare that they have no competing interests.

Funding
This research was funded by the National Public Welfare Industry Scienti c Research Master (201202010). These institutions had no further role in the study design, the collection and analysis of data, the writing of the report, and the decision to submit the paper for publication.

Authors' Contributions
FBT conceptualized the study and developed the interview guide. YZ and XYW conduced the qualitative analysis and QLW conducted the quantitative analysis. YZ drafted the manuscript. RJW, QZ, TTL contributed signi cantly to the drafting and revising of the article. All Authors read, commented and approved the nal manuscript.