Joint association of screen time and physical activity on self-rated health and life satisfaction in children and adolescents: the CASPIAN-IV study

Abstract

Introduction

Assessment of health, well-being and health-related quality of life might be either subjective or objective. Self-rated health is a subjective measure for assessing the health status of a population. It is a simple assessment in which individuals are asked to rate their general health status as good or poor (sometimes excellent and other variants might be added). This concept can contain mental and physical health as well as functional capacity of the participant. Inevitable evidence indicates an influential role for self-rated health in impacting a diverse range of health outcomes, in both early and later life. For instance, the role of self-rated health in predicting morbidity and mortality has been investigated since long ago, suggesting a reverse association between good self-rated health and later life mortality.^1–3 Studies published in the latest decade have also confirmed these results.^4–6 Findings indicate the ability of self-rated health for predicting mortality to be independent of other health status determinants such as morbidity, chronic diseases and functionality.⁵ The association between self-rated health and later life mortality is mostly discussed and noted in adults, whereas adolescents often demonstrate self-rated health correlation with other health outcomes rather than mortality, namely psychosocial functionality, health behaviors, subjective health complaints and health service attendance.^7,8 A 2012 adolescent study also revealed a higher rate of school dropouts in adolescents who reported poorer self-rated health, in addition to a higher predicted 5-year risk of receiving insurance benefits.⁹

Life satisfaction as a part of subjective well-being, is the judgment and evaluation of the individual about how they perceive life globally.^10,11 In fact, subjective well-being consists of three concepts including positive affect, negative affect and life satisfaction, which is defined as how an individual balances positive and negative effect.¹² Poor life satisfaction is strongly associated with higher adult mortality and acts as a risk factor independent of other threats to health, such as injuries and comorbidities.^13–15 Therefore it could be used to predict and assess health-related quality of life (HRQoL).¹⁶ Similar to self-rated health, life satisfaction shows stronger associations with specific health outcomes such as psychosocial functioning, low rates of behavioral problems¹⁷ and violence¹⁸ in adolescents.

Due to the significance enumerated for self-rated health and life satisfaction, several studies have investigated their influential determinants on a global level with few of them being conducted in the Middle East and North Africa (MENA) region. Perceived weight status (or body image) is one of the factors influencing self-rated health in adults.¹⁶ In particular, family social status and income,¹⁹ school achievements,²⁰ family environment, being over or underweight,²¹ nutrition status^22,23 physical activity and screen time^24,25 have been proposed as predictors of self-rated health among adolescents.

Several world-wide studies have also suggested that factors including BMI, perceived weight status,¹⁶ psychosocial and demographic characteristics^15,26 could determine life satisfaction in adults. BMI, perceived weight status,^27,28 physical activity and screen time^25,29,30 have revealed validity for predicting life satisfaction in adolescent world-wide studies.

Although studies investigating the determining factors of self-rated health and life satisfaction in the MENA region are scarce, there is some evidence indicating predictive roles of gender³¹ and economic status³² for self-rated health in adults. Studies of this region also note the significant association of body image with self-rated health in adolescents.²⁷ Some studies have suggested BMI, perceived weight status²⁷ and being bullied by peers³³ to have a determining association with life satisfaction in adolescents of the MENA region.

Significance of both self-rated health and life satisfaction in predicting and assessing adolescence health highlights the need for controlling their determinants. As was mentioned before, many studies have remarked on the influential role of health behaviors (such as tobacco use, sleeping habits and diet) and their impact on life satisfaction and self-rated health in adolescents.^34–36 Sedentary life style is included among many health behavior risk factors with suggested negative impact on health.^37–41 Prolonged screen time is a marker of sedentary behaviors, and indicates situations with low expenditure of energy⁴² including the time spent watching television (TV), playing video games and leisure time computer work. Screen time and low physical activity are considered unhealthy behaviors.⁴⁰

It is well documented that prolonged screen time starting from childhood and continued in adolescence to adulthood,^43–45 is among the responsible factors for obesity^46–48 and downstream non-communicable diseases like diabetes mellitus, metabolic syndrome and cardiovascular diseases.^49,50 With regards to a large national study in the US, participants of 8 to 18 years of age spent an average of 4.5 hours watching TV and 1.5 hours working with a computer.⁵¹ Watching TV is associated with hypertension, hypercholesterolemia, sleep disorders, aggressive behaviors and mood disorders, which could all influence how an individual perceives life satisfaction and self-rated health.⁵² Furthermore, media itself might have direct impact on the formation of body self-image and life satisfaction (e.g., by food advertisements and film characters), and could indirectly influence feelings and weight perception.^39,53–55 This altered self-image can subsequently alter life satisfaction. In fact, body dissatisfaction can be more of a threat than obesity itself, since few recent studies (in both adolescents and adults) suggested the impact of body image on self-rated health and life satisfaction to be independent of actual weight.^16,27

On the other hand, physical activity is shown to be associated with adolescents’ mental and physical health through several mechanisms such as mediating weight,⁵⁶ perceived health status,⁵⁷ quality of life and self-image in addition to various physical health benefits.⁵⁸ Moreover, since introduction of self-rated health and life satisfaction, the role of physical activity in impacting self-rated health^57,59,60 and life satisfaction^{23,29,61–63} has been investigated and advocated. Some studies suggested that prolonged screen time would inevitably reduce physical activity, or at least a co-occurrence between low physical activity and high sedentary behaviors exists.⁶⁴ However several studies indicated opposite findings that screen time and physical activity might alter health dimensions independently, and should be considered as two different entities with independent measurements.^65–68 While searching the literature, it was revealed that joint association of physical activity and screen time has been mostly investigated regarding their effects on metabolic risk factors such as obesity and overweight^69,70 rather than self-rated health and life satisfaction; a few of them compared the effects of screen time and physical activity as independent risk factors, reporting screen time to be the stronger predictor of overweight.^71,72

Prior studies indicated the role of screen time and physical activity in influencing life satisfaction and self-rated health, but it seems that research comparing their effects are scarce, specifically in pediatric and adolescence populations. Furthermore, most of the studies investigating screen time and physical activity in adolescents were conducted in western countries. While like many other countries a considerable number of Iranian children and adolescents have sedentary habits and prolonged screen time,^73,74 no study has investigated the effects of prolonged screen time and inactivity (low physical activity) on adolescent health outcomes such as self-rated health and life satisfaction. Therefore it seems a gap of knowledge exists in this regard.

Therefore this study aims to investigate the association of physical activity, screen time and their possible combination, with life satisfaction and self-rated health in a sample of nationally representative Iranian adolescents who participated in the CASPIAN-IV study.⁷⁵ Furthermore, by comparing the impacts of physical activity and screen time, it aims to determine which one of them is a stronger predictor of life satisfaction and self-rated health in Iranian adolescents.

Methods

Participants and study design

This study is a part of a nationwide study, the fourth survey of Childhood and Adolescence Surveillance and Prevention of Adult Non-communicable Diseases, also known as CASPIAN-IV (2011–2012). A total of 14 880 children and adolescents from elementary, intermediate and high schools of rural and urban areas, of 6–18 years of age are included in this survey. They were selected through multi-stage cluster sampling from urban and rural areas of 30 provinces of Iran. Based on the proportion of rural to urban student population, an equal number of girls and boys were selected in 48 clusters of 10 students for each province. The methodological aspects of this survey are described in detail in a previous study.⁷⁵ Verbal and written consent was obtained from individuals and their parents. Ethical approval was obtained from the ethical committees of Tehran and Isfahan University of Medical Sciences.

Two validated questionnaires were given to children and one of the parents, in order to gather data on screen time, physical activity and other demographic variables. These questionnaires were designed based on the WHO Global School-Based Student Health Survey (WHO-GSHS).⁷⁶ Student questionnaires consisted of questions about life satisfaction, self-rated health, physical activity and screen time. Trained personnel completed student questionnaires in calm and supervised environments inside the schools. Parent questionnaires were also completed by skilled interviewers and included questions about family socio-demographic characteristics.

Physical variables were evaluated using calibrated equipment under standard protocols and by professional trained health-care workers. Weight was assessed to the nearest 0.1 kg on a scale placed on the ground while subjects were weighed without their shoes and with light clothing on. Height was measured without shoes to the nearest 0.1 cm. BMI was computed through dividing weight (kg) to height squared (cm²).

Definition of terms

For the purposes of this study, screen time was addressed in two parts, time spent on watching TV and time spent on computer working; students were asked for time spent in hours per day. For the analysis of screen time, according to the international screen time recommendations, prolonged screen time was defined as watching TV, computer work and sedentary behavior (screen time in general) for more than 2 hours a day.⁷⁷ Physical activity was estimated by two questions: ‘In how many days were you physically active for overall 30 minutes per day during past week?’ where response options ranged from 0 to 7 days; and ‘On a regular basis, how much time do you spend in physical education (PE) class in school per week?’ where response options ranged from 0 to 3 or more hours. Physical activity less than 2 hours per week was considered as low, 2–4 hours a week was considered as moderate and more than 4 hours a week was considered high physical activity.⁷⁶ A possible joint or combination of these two variables (screen time and physical activity) was developed for the purpose of this study, in which the worst scenario is having prolonged screen time and low physical activity and the best scenario is having low screen time and high physical activity.

Current smoking was considered positive when students reported use of tobacco products such as cigarettes and hookah every day. Passive smoking was considered positive when students reported others smoking in their presence. Weight was expressed using BMI cut-off points provided by WHO and were defined as underweight (BMI <5th percentile), healthy weight (BMI 5th to <85th percentile) and overweight (BMI 85th to <95th percentile). Students’ perception of their weight status was evaluated using the question: ‘How do you perceive your body?’ where response options consisted of underweight, appropriate weight (about right) and overweight. Depression and anxiety were estimated using two questions: ‘During the past 12 months, did you ever feel so sad or hopeless almost every day for 2 weeks or more in a row that you stopped doing your usual daily activities?’ (Response options: no and yes); and ‘During the past 6 months, how often did you experience anxiety so that you could not perform your daily activity?’ (response options: almost every day, more than once a week, almost every week [considered as yes]; almost every month, and rarely or never [considered as no]).

The methods and variables used for calculating socioeconomic status were approved in the Progress International Reading Literacy Study for Iran.⁷⁸ Socioeconomic status score was estimated using the principle component analysis method based on parents’ education and job, type of school (private or governmental), type of home (private/rented) and family assets (private car and computer). The socioeconomic status score for each student was a weighted average of the socioeconomic status variables. The weighted averages of these variables were summarized under one main component named socioeconomic status score. This component explained 59% of variance. Students were classified as low, moderate and high socioeconomic status based on this component.

‘How would you describe your general state of health?’ was the single item used for self-rated health categorized in two groups: ‘poor’ and ‘good’.²¹ For life satisfaction, subjects were asked to indicate their degree of life satisfaction by using a ten-point scale from 1: very dissatisfied to 10: very satisfied. Scales less than 6 were considered as ‘not satisfied’ and scales 6 and over were defined as ‘satisfied’.

Categorical variables are presented as number and percentage. Continuous variables are reported with SD. Mean of age between sexes were compared using T-test; χ² was used to assess association of categorical variable with sex. Association of screen time and physical activity with self-rated health and life satisfaction were assessed using χ² test. Logistic regression analysis is performed for evaluating the association between self-rated health and life satisfaction with physical activity, screen time and their combination. Four models are defined for each association: Model I represents the crude association between screen time or physical activity or their combination with self-rated health or life satisfaction; Model II represents former association adjusted for age, sex and region; Model III represents additional adjustment for socioeconomic status, BMI, passive smoker, active smoker, anxiety, depression, body image, birth order; Model IV offers additional adjustments for screen time (regarding physical activity) and physical activity (regarding screen time). Data were analyzed using survey data analysis methods in STATA Corp 2011 Release 12 (StataCorp LP, College Station, TX, USA.). A p-value of <0.05 was considered statistically significant.

Results

In this nationwide survey 13 486 children and adolescents completed the survey (response rate: 90.6 %). Baseline characteristics of the study population are shown in detail in Table 1. The study population consisted of 6640 girls and 6846 boys, with a mean age of 12.47 (SD 3.36). As shown in this table, 24.4% (3295/13 486) of students were from rural areas and the remaining 75.6% (10 191) came from urban areas. Among participants, 21.6% (2871/13 322) had excess weight. Prolonged screen time and low physical activity were observed in 18.6% (2494/13 393) and 34.1% (4553/13 349) of the study population, respectively. About 50% of both boys (3460/6760) and girls (3300/6585) reported watching TV more than 2 hours a day, however 12.3% (811/6610) of boys spent more than 2 hours a day in computer work, compared with only 6.9% (449/6470) of girls. In addition, prolonged screen time (more than 2 hours) was reported in 21.9% (1489/6790) of boys compared with 15.2% (1005/6603) of girls; 71.2% (4820/6765) of boys and 60.4% (3976/6584) of girls reported moderate to high physical activity. When considered as a combined variable, only 6.3% (883/13 315) of participants had low physical activity and prolonged screen time. On the other hand, 53.9% (7180/13 315) had healthy behavior with regards to these two variables; that is, 30.6% (4072/13 315) were categorized in the group of low screen time–moderate physical activity and 23.3% (3108/13 315) had low screen time and high physical activity. Overall 10 683 out of 13 360 (79.96%) rated their health status as being good (good self-rated health) and 10 698 out of 13 387 (79.91%) were satisfied with life (favorable life satisfaction).

Tables 2 and 3 represent associations of physical activity and screen time with self-rated health and life satisfaction by sex and in the whole population. Based on this report, in the whole population, life satisfaction and self-rated health are significantly associated with physical activity and screen time (both components: computer work and watching TV). Among those students who considered their health status as good, most had a screen time of less than 2 hours. The same pattern was observed in life satisfaction. Also, it should be noted that in boys the highest optimal ratio of self-rated health was reported most in groups of high physical activity with low screen time (1548, 84.0% reported good self-rated health) or prolonged screen time (462, 84.5% reported good self-rated health). A similar pattern was also reported in girls, with a slight preponderance towards those with low screen time (1058, 84.7% reported good self-rated health). Life satisfaction analysis also yielded similar results since the highest ratio of optimal life satisfaction in both genders was reported in the low screen time–high physical activity group (1533, 82.9% in boys and 1082, 86% in girls).

The logistic regression analysis is shown in Table 4. In crude model high physical activity was associated with good life satisfaction (OR 1.7, 95% CI 1.50–1.91) and self-rated health (OR 1.64, 95% CI 1.45–1.85) while prolonged screen time correlated inversely with good life satisfaction (OR 0.84 95% CI 0.75–0.94) and self-rated health (OR 0.87, 95% CI 0.78–0.97). In multivariate analysis only high physical activity was associated with good self-rated health (OR 1.37, 95% CI 1.20–1.57) and life satisfaction (OR 1.39, 95% CI 1.21–1.59) and prolonged screen time was not associated with good self-rated health (OR 1.02, 95% CI 0.90–1.16) and life satisfaction (OR 0.94, 95% CI 0.82–1.07). Among all possible combinations of physical activity and screen time in multivariate analysis, the low screen time and high physical activity combination had the highest OR for both good self-rated health (OR 1.37, 95% CI 1.18–1.59) and life satisfaction (OR 1.43, 95% CI 1.23–1.67).

Discussion

The current study revealed that although the crude association of both prolonged screen time and high physical activity with life satisfaction and self-rated health were significant (physical activity with a direct and screen time with an inverse impact), in multivariate analysis only high physical activity demonstrated a significant association. Screen time loses its significant inverse association after adjustment for different socioeconomic and demographic variables and does not affect life satisfaction and self-rated health significantly, meaning that any amount of screen time (high or low) could be accompanied with favorable life satisfaction and self-rated health. Therefore our findings support the independent influence of physical activity on health; and oppose the ‘displacement hypothesis’ in which an increase in screen time results in poor physical activity and automatically affects self-rated health and life satisfaction adversely as health outcomes. In other words, although the amount of time spent in front of TV and computer (screen time) is a factor with negative impact on self-rated health and life satisfaction (through mediating effects of other independent variables such as BMI and weight perception), the impact can be overshadowed by more intense and effective physical activity, in addition to modifying the factors that can indirectly mediate through screen time (such as BMI and body image). Current data support physical activity as the significant determining factor compared to screen time; nevertheless the fact that the combination of low screen time and high physical activity have the best self-rated health and life satisfaction should not be neglected.

In this survey, approximately 80% of the study population (10 683 individuals), reported ‘good’ self-rated health; 21.6% of them (2871) were overweight and 50% (6760) had a TV time of more than 2 hours a day. Some studies have reported higher rates of good self-rated health among children or adolescents. For instance, Herman et al.⁷⁹ investigated the impact of physical activity, sedentary behaviors and BMI with self-rated health in 527 children (mean age 9.5) at risk for obesity; 40% of children in that study were overweight or obese and 30% reported that they spent more than 2 hours a day watching TV. Self-rated health was good to excellent in 97% of children.⁷⁹

Prior studies have noted the association of screen time and physical activity with HRQoL indicators. One study examined the association of screen-based media and physical activity with indicators such as self-perceived health and emotional well-being in German adolescents. It was concluded that higher physical activity was significantly associated with higher HRQoL in a dose-response manner, a finding consistent with our results. Additionally, higher screen-based media was associated with lower HRQoL domains. The effects of screen-based media and physical activity were not compared to each other in the mentioned study.⁸⁰ A similar study of physical activity, screen-based media and their association with HRQoL in 3040 Australian adolescents, reported that more than 2 hours a day of screen-based media, and low physical activity were associated with lower HRQoL.²⁴ Another study in 881 adolescents in Mexico, revealed that physical activity on at least 4 days a week and screen time less than 2 hours a day were associated with higher quality of life.⁸¹ However, none of these studies aimed to combine screen time and physical activity in one joint variable to compare their combined effect.

In a recent study conducted by Herman et al.⁸² in adolescents, the role of screen time and physical activity in impacting self-rated health was investigated. In this study, the effects of both physical activity and screen time were adjusted for one another and therefore the final results reported independent impacts on self-rated health. Although the effects of physical activity and screen time were not compared by using a joint (combined) variable, they were adjusted for each other using multiple logistic regression and therefore it was revealed that the association between screen time and self-rated health was weaker than physical activity in magnitude. Herman et al.⁸² and our study both agree on the independent and dominant role of physical activity over screen time. However the significant association between screen time and self-rated health was rejected in the current study, suggesting no determining role for it in predicting self-rated health.

Another study conducted by Iannotti et al.⁸³ investigated the interrelationship of screen-based media and physical activity on different domains of social and psychological health including perceived heath and satisfaction with quality of life, resulting in similar findings regarding the independence of physical activity and screen-based media. This study suggested that the effect of screen-based media is not overshadowed by physical activity when they are both in the equation. Eventually, this study premiers none of two variables over another. It rejects the ‘displacement hypothesis’ and accepts physical activity and screen time as self-determining health factors, which is consistent with findings of the current study in regards of independency of physical activity from screen time, even though it contradicts our findings by suggesting a significant impact for screen time.⁸³

A 2014 meta-analysis by Pearson et al.⁴² also investigated the role of ‘displacement hypothesis’ in physical activity and sedentary behaviors (which asserts that engaging in one area may displace the other one); it revealed no support for their direct substitution effect and therefore it was concluded that their effects on health outcomes are independent of each other. Similar to our current paper, this study used joint association of physical activity and screen time to compare their effects on health outcomes such as self-rated health; and the highest self-rated health was observed in the subgroup with low screen time and high physical activity. It was asserted that physical activity is stronger than screen time as individuals with no or insufficient physical activity experienced worse health regardless of their high or low screen time; these data are supportive of current research findings.⁴²

In one study conducted in Australian adolescents comparing the effects of screen time and physical activity on weight status, role of screen time was estimated stronger than physical activity.⁷² In other words, increased weight was more strongly correlated with prolonged screen time rather than low activity, which opposes our findings. This could be explained by the difference in investigated health outcome.

To the best of our knowledge, the present study is the first Iranian research that investigated the joint association of physical activity and screen time on self-rated health and life satisfaction in a population-based pediatric group. It is also the first study of this kind in the MENA region. As was mentioned before, many studies have noted the effects of screen time and physical activity on different health outcomes in children and adolescents, but mostly indicated their effects without comparing them together; in addition to the fact that HRQoL indicators such as self-rated health and life satisfaction have not been getting enough attention. Therefore, further studies are required on this matter, specifically in Middle-Eastern children and adolescents.

Strengths and limitations

The main limitation of the current study is the cross-sectional design, which makes it difficult for causal inference of these associations. Another limitation is the subjective method of assessing screen time and physical activity, which could be considered imprecise compared to objective methods.

The main strengths of this study are its large sample size, nationwide coverage, and considering adjustment for different variables. The other novelty of this study is considering physical activity, screen time and their combined associations with self-rated health and life satisfaction.

Conclusions

The current findings revealed that although prolonged screen time is associated with lower self-rated health and life satisfaction in crude model, this effect is compensated to some degree by moderate and high physical activity. These results suggest that physical activity and screen time are two different and independent health factors and do not collaborate or displace each other automatically. Moreover, an increase in one's effect does not mean a reduction in the other. Although improving both physical activity and screen time in adolescents is useful and advantageous, high screen time in adolescents could be waived by having an optimal physical activity; therefore, improving physical activity rather than emphasizing reduction in screen time would be more beneficial to children and adolescents’ health in terms of a more optimal self-rated health and life satisfaction. In conclusion, designing behavioral amendment protocols in children and adolescents entails great attention to physical activity, more than it requires amending screen time and sedentary behaviors; also more future studies on physical activity and screen time of adolescents are crucial owing to the scarcity of knowledge on this matter.

Authors’ contributions: MQ, RK, RH, MEM and GA designed the study. NMG, HA, SS and TA were involved with data acquisition. NM, MQ, SD and RH participated in statistical analysis and drafted the manuscript. NM was contributed in drafting of manuscript. Critical revision was done by RK, MQ, SD. MQ and RH are guarantor of the paper

Funding: None

Competing interests: None declared.

Ethical approval: The ethical committee of Tehran and Isfahan University of Medical Sciences and Ministry of Health and Ministry of Education approved the study.

References