The associations between screen time-based sedentary behavior and depression: a systematic review and meta-analysis

The use of computers/TV has become increasingly common worldwide after entering the twenty-first century [1], and there has been a large increase in the number of workers whose major job is computer-related [2, 3]. Moreover, both adolescents and adults also spent a large amount of time on the computer or smartphone or watching television. With advances in technology, screen time (ST), including watching television, using a computer and playing video games, is becoming a central component of the daily lives [4] and the most common sedentary behavior [5] (i.e., activities that require minimal body movement resulting in low energy expenditure similar to that at resting level [1.0 to 1.5 metabolic equivalents (METs)] [6]). Previous studies have shown that screen time-based sedentary behavior (ST-SB) is associated with increased risk for a variety of physical diseases, such as cardiovascular disease [7], obesity [8], and diabetes [9]. Moreover, ST-SB also influences mental health, such as sleep problems [10], anxiety disorders [11] and depression [12].

Currently, mental disorders are widely recognized as a major contributor (14%) to the global burden of disease, and depression is one of the most prevalent mental disorders [13]. Indeed, the World Health Organization (WHO) ranked major depression as one of the most burdensome diseases in the world [14]. Major depression has increased from the 15th-leading cause of adult disease burden in 2000 to the 11th-leading cause in 2010 [15]. According to new estimates of depression released by the WHO, the number of people living with depression increased by 18% between 2005 and 2015. Depressive disorders are ranked as the single largest contributor to nonfatal health loss (7.5% of all years lived with disability). The prevalence varies across the world, from a low incidence of 2.6% among males in the Western Pacific Region to 5.9% among females in the African Region. Furthermore, depressive disorders are projected to be the second leading cause of disease burden worldwide by 2030 and are the leading cause in high-income countries [16]. In addition, the onset of depression is common in adolescents and young adults [17‐19], who may spend much more time on computers than older persons, coinciding with a pivotal period of physical and psychological development, and can lead to poorer psychosocial functioning, lower life and career satisfaction, more interpersonal difficulty, higher need for social support, more comorbid psychiatric conditions, and increased risk of suicide.

The median age of onset (50th percentile on the age-of-onset distribution) was approximately 30 for major depressive disorders [20]. Currently, many adults study or work in front of computers, and ST-SB has become a common and important issue not only for adolescents but also for adults. Therefore, understanding the association between ST-SB and the risk of depression among adults is also important to the development of prevention and intervention strategies. Many studies have investigated the association among different populations; however, the results were inconsistent. Some studies showed that longer ST might lead to a higher prevalence of depressive-related problems, while some studies thought this association was not significant. Thus, this systematic review was conducted to explore whether ST-SB influenced the risk of depression.

This study aimed to investigate the association between ST-SB and depression with a meta-analysis, as previous studies showed inconsistent results. The results of the meta-analysis showed that most of the subjects with more than 2 h/d ST-SB were more likely to have depression. When ST was considered as a continuous variable, the associations between ST and depression became small yet remained statistically significant. Some mechanisms may explain the relationship between SB and the risk of depression. First, long-term SB might give rise to biological pathway disturbances including central nervous system arousal or sleep disturbances [45, 46]. Second, physical activity has been shown to be beneficial for reducing depressive symptoms [47]. However, some studies showed that even when controlling for physical activity and other demographic variables, the populations that reported high levels of screen time were more likely to be depressed than those who did not, suggesting that the effects of screen time are independent of physical activity [31]. Another explanation refers to social interaction: prolonged sedentary behaviors, such as television viewing, may lead to social solitude and withdrawal from interpersonal relationships, which have been linked to increased feelings of social anxiety [48]. Furthermore, these studies also showed a positive association between SB and obesity, which is explained by the mechanism through which SB is associated with energy-dense snack consumption and snacking behavior [49], and depression has been shown to be associated with obesity [50, 51].

In addition, according to the results of the subgroup analysis, there were significant differences between these associations in females and males. In the female population, the association was significant, while in the male population, it was not. This might be because of the increasing prevalence of mental health problems among females [52]. Furthermore, men and women use different coping mechanisms when dealing with depression. Women are more likely to internalize and ruminate on their condition, whereas men are more likely to engage in externalizing or distracting activities [53]. Thus, when screen time increases, females would likely have less time to communicate with others and would become more introverted, whereas males may shift their attention to other affairs. Thus, excessive time devoted to media may affect female users more substantially [54]. Moreover, using different reference categories led to different results. There was a week association between SB and depression risk in studies using 0–1 h/day as the reference category, while the association became stronger when using 2 h/day or more as the reference category. This finding provides better clarification of the association between ST-SB and depression risk, indicating that ST in moderation may not be associated with higher levels of depression. One hypothesis was that there was a curvilinear dose-response association between ST and the risk of depression. Some guidelines and recommendations [55] emphasized an overall positive association between ST-SB and morbidity risk. However, studies have shown that when ST is limited to 0–2 h/day, ST-SB is associated with a lower risk of depression, and the lowest risk is detected at ST of 1 h/day [4]. The selection of reference categories should be considered in future studies on SB. The results of the subgroup study by study design showed a consistent association in cohort and cross-sectional studies, but the heterogeneities were different, potentially because of the methodological limitations of cross-sectional studies. To demonstrate the association, cohort studies could provide higher grade evidence than cross-sectional studies [56].

Some caveats must be discussed. As the heterogeneity was quite high (approximately 90%), the factors that mainly explained this heterogeneity must be explored. Based on the results of the subgroup analysis, we found that gender, reference group and study design influenced the heterogeneity of the overall meta-analysis. In addition, distinct from chronic diseases such as hypertension, which could be diagnosed by objective indicators, information about depression disorders or depressive symptoms was often collected according to self-reported respondent answers to questions. The fieldwork of different studies was carried out by different interviewers, and the diagnoses could vary even though the instruments were the same. Moreover, there were several limitations to this review. First, most studies employed a cross-sectional study design, so these studies were limited by several methodological weaknesses. The cross-sectional character of these studies does not allow causal inferences to be made because relationships were unable to be determined. Second, SB was measured using retrospective self-report measures in most of the studies, which is subject to recall bias. In addition, mental health was possibly underestimated by respondents because of the stigma associated with psychological questions. Third, uncontrolled variables may have influenced the results. In this review, some studies controlled only social demographic variables such as age and gender, while physical activity and weight were also included as covariates in some studies. Further studies with proper controls for relevant covariates are needed to clarify this issue.

In future studies, valid objective measures of sedentary behavior are needed. Not only the dose (e.g., frequency, duration) but also the context (e.g., TV viewing, computer use, smartphone use) should be included in a structured or semistructured questionnaire. Additionally, some objective measures of sedentary behavior (e.g., accelerometers and posture monitors) are recommended. Moreover, some studies have focused on the linear or nonlinear relationships between ST-SB and depression [57, 58]. Further studies should be carried out to estimate the dose-response relationship between ST-SB and depression, exploring the appropriate time limit for ST-SB.

ST-SB is associated with a higher risk of depression, especially when it exceeds 2 h/day. In the female population, the association between SB and risk of depression is significant, while in the male population, no significant associations were observed. Our review supports the current recommendations of limiting ST to promote mental health, especially in women. In addition, valid objective measures of sedentary behavior should be developed in future studies to explore appropriate time limits for ST-SB.