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Passive Versus Mentally Active Sedentary Behaviors and Depression

Hallgren, Mats1; Dunstan, David W.2,3; Owen, Neville4,5

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Exercise and Sport Sciences Reviews: January 2020 - Volume 48 - Issue 1 - p 20-27
doi: 10.1249/JES.0000000000000211
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Abstract

Key Points

  • Emerging evidence suggests that sedentary behaviors may have detrimental associations with depression, but relevant findings are inconsistent and limited mainly to observational studies.
  • Our original studies have identified differential associations of passive (e.g., television viewing) and mentally active (e.g., reading) sedentary behaviors with depression, where the former seem to increase the risk of depression, whereas the latter may protect against depression onset.
  • To take the science forward, a more systematic approach to the classification of sedentary behaviors is needed, considering both the contexts and type of sedentary behavior measured.
  • Plausible but currently still speculative mechanisms include psychosocial factors and biological pathways linked to the etiology of depression.
  • There are new research opportunities relating to measurement, underlying mechanisms, and the overall need to identify causal relationships.

INTRODUCTION

Depression is a debilitating mental health problem associated with socio-occupational impairment and high levels of somatic comorbidity, which can be ameliorated by physical activity and exercise. Clinical presentation of depression can vary widely; it may be experienced as a transient lowered mood state that falls below the threshold for clinical depression or, in other instances, as a mild to severe major depressive disorder (MDD) that tends to be recurrent and requires ongoing treatment. Unless otherwise specified, the term depression is used throughout to describe MDD. The lifetime prevalence of depression differs by age, gender, and income, but typically ranges from 10% to 20% (1). Efficacious treatments exist, but poor adherence and limited effectiveness highlight the need for an improved understanding of factors associated with depression onset and relapse. Knowledge gained could inform strategies aimed at preventing depression and may have implications for optimizing treatment regimes. Within this context, physical activity has received considerable research attention. Low levels of physical activity are consistently associated with an elevated risk of depression, whereas structured physical activity (exercise) is an effective treatment for mood disorders (2,3).

As distinct from insufficient physical activity (i.e., not meeting specified physical activity guidelines), sedentary behavior has been operationalized as any waking activity characterized by an energy expenditure of ≤1.5 metabolic equivalents and a sitting or reclining posture (4). Common sedentary behaviors include television (TV) viewing, computer use, driving, and reading, and various environmental factors are shown to influence these behaviors (5). High volumes of sedentary time are prevalent in adult populations and have been documented in studies using objective assessments (accelerometers/inclinometers). A study from the United States involving 7985 middle-aged and older adults reported that sedentary behavior accounted for 12.3 h of a 16-h waking day (6). Data from a nationally representative U.S. health survey showed that the estimated prevalence of sitting and watching TV or videos for ≥2 h d−1 was 65% among adults, and 85% among those aged ≥65 yr. During the 13 yr preceding 2016, prevalence of computer use (≥1 h d−1) during leisure time increased among all age groups, and total sitting time increased among adolescents and adults by approximately 1 h d−1 (7).

High volumes of time spent sitting have been linked to increased risk of cardiovascular disease, type 2 diabetes, and all-cause mortality (8,9). Time spent in leisure-time moderate-to-vigorous physical activity attenuates, but does not eliminate, these associations, except among those in the highest category (≥60 min d−1), where physical activity seems to eliminate the increased risk of death associated with high sitting time (10). A recent review identifies sedentary behavior as a major preventive health issue and highlights ways in which this emerging knowledge base can inform public health strategy (11).

Those with depression are less physically active and more sedentary than their nondepressed counterparts. A systematic review of 24 studies (n = 2901) found that, compared with nondepressed controls, adults with depression spent on average less time in overall physical activity and in moderate-to-vigorous activity, and had significantly higher volumes of sedentary behavior [standardized mean difference (SMD) = 0.09, 95% confidence interval (CI) = 0.01–0.18] (12). The proportion of those with depression not meeting the recommended physical activity guidelines was 67.8% (85.7% when measured objectively), significantly higher than nondepressed controls. Those with depression experience a premature mortality gap of approximately 8–10 yr compared with the general population (1). This gap in average life expectancy is largely attributable to preventable health conditions, such as cardiovascular disease, which is more prevalent in depression (1), and can be reduced through lifestyle interventions that promote physical activity.

Strategies that encourage more physical activity and less sedentary behavior are now recommended for preventive health benefits. General recommendations relating to sedentary behavior have been incorporated into the Physical Activity Guidelines for Americans (Second Edition) (13). Given the established links between physical inactivity and poor mental health, replacing sedentary behaviors with physical activities could mitigate an important risk factor for depression, while also contributing to improved cardiometabolic health. Although still largely speculative, emerging evidence (see the section on “What mechanisms could underlie these relationships?”) suggests that there are plausible biological processes that may connect extended sedentary time with depression onset and relapse.

We briefly review the available evidence, mainly from observational studies, concerning relationships of sedentary behavior with depression and propose six research questions to take the science forward. Central to this review is a novel hypothesis that there are potential differential associations of passive (e.g., TV viewing) and mentally active (e.g., reading) sedentary behaviors with depression. Relatedly, we argue that a more systematic approach to the classification of sedentary behaviors is needed, which considers both the context and type of behavior measured. We present a conceptual framework to facilitate this goal. Potential mechanisms underlying the role of sedentary behavior in depression are considered, research opportunities relating to measurement are discussed, and potential clinical and public health implications of future research findings are considered.

Sedentary Behavior–Depression Relationships

Research exploring links between sedentary behavior and depression is a new field, and findings are currently limited mainly to observational studies. Overall, these identify deleterious associations of sedentary behavior with depression. In a meta-analysis, the pooled risk ratios of depression (assessed using validated clinical tools or clinician diagnosis) for sedentary behaviors were 1.31 (95% CI = 1.16–1.48) in 13 cross-sectional studies, and 1.14 (95% CI = 1.06–1.21) in 11 longitudinal studies (14). An updated meta-analysis of prospective studies (n = 14; 134,912 participants) reported a significant positive association between a common leisure-time sedentary behavior (TV viewing) and risk of depression [risk ratio (RR) = 1.11, 95% CI = 1.03–1.19] (15). In subgroup analyses, TV viewing was also positively associated with clinician-diagnosed depression (RR = 1.08, 95% CI = 1.03–1.14); however, the association of “computer use” with depression was not statistically significant. These recent reviews have included studies with large participant samples followed over several years. One U.S. study examined prospective (10-yr) relationships of physical activity, TV viewing time, and incident depression in 49,821 women (16). Higher physical activity levels reduced the risk of subsequent depression, whereas higher levels of TV viewing time (≥21 vs 0–1 h wk−1) significantly increased the risk of incident depression (16). Although most studies have not examined the joint associations of physical activity and sedentary behavior, a recent study using accelerometers found that the more sedentary that participants were in their everyday life, the less well and less energized they felt (17).

Isotemporal substitution modeling has been used previously to estimate the effects on body weight and the risk of chronic disease of substituting different durations of physical activities of different intensities (18); this method recently has been applied to examining relationships of sedentary behavior with mental health. In a cross-sectional study involving 276 older adults, Yasunaga et al. (19) found that replacing 30 min d−1 of sedentary behavior with 30 min d−1 of light physical activity was negatively associated with self-rated depression. Mekary et al. (20) examined prospectively the associations of different activities with various activity displacements and depression risk among 32,900 U.S. women over 10 yr. An isotemporal substitution gradient was found for TV viewing, such that replacing 60 min d−1 of this activity with 60 min d−1 of brisk walking was associated with lower depression risk.

Although most reviews report deleterious relationships of sedentary behavior with depression, both in adults (14,15) and adolescents (21), some individual studies have not found such associations or have reported moderating effects of gender. Teychenne et al. (22) examined prospective relationships of sedentary behaviors (TV viewing, computer use, overall sitting time, and screen time) with risk of depression in socioeconomically disadvantaged women aged 18–45 yr. No significant associations were observed between any sedentary behavior variables and depression during the 3-yr follow-up, although depressive symptoms were associated cross-sectionally with higher levels of TV viewing time (≥240 min d−1). In a 2-yr study examining associations of TV viewing, Internet use, and reading with mental health, TV viewing time at baseline (≥6 vs <2 h) was associated with more depressive symptoms and worse global cognitive functioning, whereas Internet use and reading were associated with less depressive symptoms (23). Many investigations have examined combined indices that include different types and contexts of sedentary behavior, an approach that does not enable potential differential effects of each sedentary behavior to be explored. One study examined longitudinal relationships over 6 yr of total self-reported sitting time with health-related symptoms in middle-aged Australian women. No significant relationships were found between total sitting time (which combined different types of sedentary behaviors, e.g., watching TV, reading, working at a computer) and depression at follow-up (24).

To identify potential causal relationships, findings from observational studies should be corroborated by experimental evidence. Two recent trials lasting 1 and 2 wk, respectively, have shown that experimentally induced time spent in sedentary behaviors in free-living conditions can have adverse effects on mood and depression (25,26). In one trial (26), sedentary behaviors (assessed using accelerometers; <190 count min−1) were linked to both negative mood states and heightened levels of inflammatory markers, suggestive of a potential underlying biological mechanism. In another study involving 39 physically active younger adults, a 1-wk reduction in daily activity levels (≤5000 steps d−1) resulted in significantly improved depression and mood scores in the intervention group versus active controls, who continued their usual physical activity levels (25).

In sum, there are preliminary indications, mainly from observational studies, that extended periods spent in sedentary behavior may increase the risk of depression. However, there are some limitations of previous research that restrict firm conclusions about these associations and the formulation of specific health-related guidelines. First, there has been an extensive focus on total rather than context-specific sedentary behaviors. Second, with the partial exception of TV viewing, studies examining associations between different types of sedentary behavior with depression remain scarce; yet, these may offer crucial insights into the specific behaviors that heighten the risk of depression and could be targeted for intervention. Third, the distinct and combined relationships of physical activity and sedentary behaviors with depression should be examined. Finally, the issue of potential reverse causality needs to be addressed. These issues are considered further in the next sections.

How Can Sedentary Behaviors Be Defined to Better Understand Their Influence on Depression?

Research into sedentary behavior and cardiometabolic health suggests that the context of these behaviors is relevant, with some contexts (e.g., leisure time) potentially exerting greater relative risks than others (e.g., transport). A cross-sectional study involving 3429 middle-aged Australian adults examined associations of sitting time in four contexts with cardiometabolic risk biomarkers (27). Overall, associations with cardiometabolic risk scores were stronger for TV viewing and computer use, and weaker for occupational sitting, and there was some evidence suggesting that the context in which people sit is relevant above and beyond total sitting time. Another study with 2800 adults examined associations of time spent sitting in cars with markers of cardiometabolic risk (28). After relevant adjustments, spending ≥1 h d−1 in cars (compared with ≤15 min d−1) was significantly associated with higher body mass index, waist circumference, fasting plasma glucose, and clustered cardiometabolic risk.

As many as 12 sedentary behavior contexts have been identified previously (29); these are often grouped into three broad categories of occupation, leisure, and transport, referring to where these behaviors usually occur. With few exceptions (22,30), studies linking context-specific sedentary behaviors with depression have been absent from the literature, yet could inform prevention initiatives with greater precision. Until recently, all sedentary behaviors have been treated as largely equivalent — that is, with an assumed detrimental relationship to depression, regardless of the type of behavior measured. However, in two recent papers (31,32), we have described how sedentary behaviors are diverse, with some being characterized by greater mental activity requirements (e.g., reading), whereas others are mentally passive in nature (e.g., TV viewing). Here, “type” refers to the nature of the activity itself. For example, TV viewing is a type of passive sedentary behavior that is normally undertaken in the context of recreation or leisure. As most work-related tasks involve concentration, occupational sedentary behaviors would logically be considered as mentally active.

Findings from our longitudinal studies suggest differential associations of passive and mentally active sedentary behaviors, where the former seem to increase the risk of depression, whereas the latter may protect against depression onset (32). In a related study involving 43,863 adults followed over 13 yr, we demonstrated that replacing 30 min d−1 of passive sedentary behavior with equivalent durations of mentally active sedentary behaviors, light physical activity, or moderate-to-vigorous physical activity reduced the hazards of depression by 5%, 13%, and 19%, respectively (31). Thus, in addition to the context, assessing relationships of different types of sedentary behavior with depression also is necessary.

Our distinction between passive and mentally active sedentary behaviors in depression research is new, although its importance has been recognized previously in related domains. Kikuchi et al. (33) examined cross-sectional relationships of passive (TV time, listening or talking while sitting, and sitting around) and mentally active (computer use, reading books or newspapers) leisure-time activities with self-reported health in older Japanese adults. Higher passive sedentary time was associated with higher odds of being overweight and engaging in lower levels of physical activity. Conversely, higher mentally active sedentary time was associated with lower odds of having low levels of physical activity (33). Psychological outcomes were also examined. Higher passive sedentary time increased the odds of psychological distress (Kessler K6 scale) but was no longer evident after adjustment for moderate-vigorous physical activity. A recent meta-analysis of prospective studies revealed that watching television was positively associated with the risk of depression (RR = 1.18, 95% CI = 1.07–1.30), whereas using a computer was not (RR = 0.99, 95% CI = 0.79–1.23) (15); this again suggests possible differential relationships of passive and mentally active sedentary behaviors with mental health.

To determine the potential impact of sedentary behaviors on depression and to underpin the development of optimal prevention strategies, future research will need to account for both the context of these behaviors (occupation, transport, or leisure) and the type of sedentary behavior being measured (passive vs mentally active). The widespread use of smartphones and other screen-based devices has resulted in the emergence of new forms of sedentary behavior (34). Assessment of these activities needs to be sufficiently nuanced to ensure they are correctly categorized as passive or mentally active in nature. On the basis of our own previous work (31,32), we suggest that grouping these diverse behaviors together could result in misleading findings and, in turn, might result in inappropriate recommendations. Here, we propose a framework for classifying sedentary behaviors based on both the context and type of behavior assessed (Fig. 1). This preliminary framework is based on our initial research findings (31,32) and evidence from related studies of sedentary behavior and depression (14). It could act as a guide for the development of future instruments to assess specific sedentary behaviors in mental health research.

Figure 1
Figure 1:
A framework for assessing sedentary behaviors across three living contexts: occupation, leisure, and transport. Within each context, sedentary behaviors are divided into two categories: 1) those that are mainly passive in nature, and 2) those involving greater amounts of mental activity. Our distinction between passive and mentally active sedentary behaviors is potentially important, as the former seem to increase the risk of depression, whereas the latter may protect against depression onset. The framework could be used to guide the assessment and categorization of sedentary behaviors in future mental health research.

What Are the Limitations of Existing Measures of Sedentary Behavior?

Given the impact of sedentary behavior on both physical health and mental health outcomes, accurate measurement of these behaviors is crucial. A review and a meta-analysis of observational studies of sedentary behavior and depression (14) show that only 2 of 24 studies used objective measures of sedentary and activity levels; the remaining studies used either the International Physical Activity Questionnaire (IPAQ) or a questionnaire developed by particular research teams, often with only one item to assess sedentary behavior. Limitations of self-report measures are well established: respondents tend to overestimate physical activity levels and underestimate durations of sedentary behavior. Although widely used, the IPAQ is limited as it includes only one item to assess sedentary behavior.

The Simple Physical Activity Questionnaire (SIMPAQ) was developed to provide a more accurate self-report assessment of time spent in all physical activities, including light activity and sedentary behavior. The instrument was designed to be sensitive to change and appropriate for use within clinical settings (35). Differences between the SIMPAQ and existing tools such as the IPAQ–short form (SF) include recommendation that the tool be used as a structured interview, features allowing for participant responses to be checked to minimize risk of significant under- and overreporting, removal of reference to physical activity intensity, and inclusion of a napping question, given the high clinical relevance of daytime sleep to the functional recovery of people living with mental illness. Unlike the IPAQ-SF, the SIMPAQ aims to capture very low levels of physical activity. This is relevant given the established acute benefits of even small amounts of activity in people with mental illness (as opposed to minimum 10-min bouts assessed by the IPAQ-SF). A forthcoming study will include criterion SIMPAQ validity data assessed against the Actigraph G13x accelerometer (35). A potential limitation of SIMPAQ’s application in mental health research is that it does not currently distinguish between passive and mentally active sedentary behaviors. Consequently, it may have greater use in routine clinical settings as a measure of physical inactivity, light physical activity, and moderate-to-vigorous activity. A review of sedentary behavior modules currently used in population surveys is presented elsewhere (36).

There is a need to develop appropriate new measures of sedentary behavior for application in mental health research, or where associations of sedentary time and cognition are being examined (37). Our preliminary framework could be informative in guiding the development of questionnaires to assess multiple types of sedentary behavior across different contexts. We also acknowledge that objective assessment of sedentary behavior using accelerometers or inclinometers remains the gold standard in physical activity research and should be adopted whenever possible. As previously suggested (38), objective measures should ideally be complimented with self-report data to identify the context in which these behaviors occur and, as we have now emphasized, whether they involve passive or mentally active behaviors.

How Do Physically Active and Sedentary Behaviors Influence Each Other and Influence Depression?

Sedentary behaviors and moderate-to-vigorous physical activity (including exercise) fall along a continuum of energy expenditures that comprise total physical activity. Regular physical activity is shown to reduce the risk of depression, while extended, uninterrupted sedentary time seems to heighten the risk (14). These two activity constructs are related; they also have been shown to have relatively independent effects on cardiometabolic health. In a harmonized meta-analysis of data from over one million men and women, Ekelund et al. (10) explored associations of sedentary behavior and physical activity with all-cause mortality in adults. Compared with the referent group [those sitting <4 h d−1 and in the most active quartile of >35.5 metabolic equivalent fortask (MET)-h wk−1], mortality rates during follow-up were 12%–59% higher in the two lowest quartiles of physical activity (<2.5 and <16 MET-h wk−1). Daily sitting time was not significantly associated with higher all-cause mortality among those in the most active quartile of physical activity. By contrast, those who sat the least (<4 h d−1) and were in the lowest activity quartile had a significantly increased risk of dying during follow-up (hazard ratio (HR) = 1.27, 95% CI = 1.22–1.31). It was concluded that high durations (about 60–75 min d−1) of moderate-intensity physical activity seem to eliminate the increased risk of death associated with high sitting time. However, in subgroup analyses, this high activity level attenuated, but did not eliminate, the increased risk associated specifically with extended TV viewing. This study is important, as it illustrates how physical activity and sedentary behaviors interact to influence major health outcomes. In the context of preventing and managing depression, a key question is “How much exercise and what type of exercise (aerobic, resistance, etc.) might be needed to counteract the adverse impacts of too much sitting?” Currently, there is insufficient evidence available to answer this question.

An important related question concerns reverse causality. To date, most studies examining associations of sedentary behavior with depression have been cross-sectional, which does not enable directionality to be established. This is problematic as depression often is characterized by mental and physical inertia. Indeed, behavioral activation techniques are used frequently in treatment to overcome the lethargy and stagnation commonly seen in depression. However, several prospectve studies have been conducted (14); these potentially provide stronger evidence of causality when adjustments have been made for baseline depression or (preferrably) when those with initial indications of depression have been removed from analyses. There is a need to examine interactions between sedentary behavior and physical activity in longitudinal studies. Additional experiemental studies also are needed.

What Mechanisms Could Underlie Sedentary Behavior–Depression Relationships?

There are some putative mechanisms that may help explain detrimental associations of sedentary behaviors with depression. One potential explanation is that sedentary behaviors could displace time spent in physical activity, which is shown to reduce the risk of depression. Another hypothesis is that prolonged sedentary time often involves socially isolated activities (e.g., TV viewing), which may remove people from supportive or mood-enhancing social interactions. Humans are social animals, and some of the most common sedentary behaviors involve isolating activities that are far removed from innately rewarding social interactions. As noted, mentally active sedentary behaviors could have protective effects against depression onset (31,32). These behaviors are ubiquitous during working hours, so context is likely to play a role in these relationships. Employment is linked to better mental health, even when it involves sedentary behavior, as it can promote a sense of autonomy, belonging, and achievement. Work can also foster supportive social relationships. Thus, the negative mood states often associated with passive sedentary behaviors could heighten the risk of depression, whereas mentally active sedentary behaviors may reduce the risk, despite equivalent energy expenditures.

Evidence from related research supports the possibility of underlying biological mechanisms, but trials of sedentary behavior interventions are needed to examine what currently are speculative links. There is evidence that depression can be linked to higher levels of some inflammatory markers, whereas an inverse association has been reported between physical activity and systemic inflammation (39). A recent systematic review of 25 interventions found consistent evidence that uninterrupted sedentary behavior results in moderate and deleterious changes in insulin sensitivity, glucose tolerance, and plasma triglyceride levels (40). A longitudinal study demonstrated associations between sedentary behavior and increases in various acute phase reactants and coagulation markers in older adults over 4 yr of follow-up. Other preliminary evidence suggests that glycemic variability may influence brain health and cognition (41). As sedentary behavior increasingly involves the use of screen-based devices, these activities also could contribute to sleep and mood disorders. Moreover, because sedentary behavior predominantly occurs indoors, away from direct sunlight, the possibility that these behaviors might reduce vitamin D exposure, which in turn is shown to affect mood symptoms, also warrants exploration.

Substituting passive sedentary behaviors with light- or moderate-intensity physical activity could reduce depression through several related mechanisms. Physical activity is shown to upregulate monoamine neurotransmission in the animal brain, changes that may be linked to mood disorders in humans (42). Exercise also seems to regulate the hypothalamic-pituitary-adrenal axis, leading to reductions in glucocorticoid stress hormones (43). Research supports the role of oxidative and nitrogen stress, and neurotrophins as key mediators in the pathogenesis of mood disorders (44). Some studies suggest that higher doses of physical activity are needed to elicit these biological mechanisms. However, a large (n = 945) trial of exercise for depression showed equivalent-magnitude effects of light, moderate, and vigorous exercise on depression severity, suggesting that low-intensity exercise can also have beneficial effects (45).

Psychosocial factors also are relevant; exercise can act as a distraction from stressful life events, improve self-esteem, and may reduce negative attentional biases. We also speculate that substituting passive with mentally active sedentary behaviors might reduce negative ruminations, which, in turn, may counteract the vicious cycle of maladaptive cognitions often seen in those who are depressed. The recurrent nature of depression and potential psychobiological mechanisms underlying relationships of mentally passive sedentary behavior with depression are illustrated in conceptual Figure 2. These links remain speculative and warrant further research attention.

Figure 2
Figure 2:
Conceptual diagram illustrating the cycle of depression (→) and our novel hypothesis of detrimental links to mentally passive sedentary behaviors (→). For many adults, depression is a recurrent disorder that involves a cycle of perceived stress, negative rumination, social withdrawal, and significant reductions in physical activity and increases in passive sedentary behavior. The figure shows the close connection between chronic depression and poor somatic health, including a higher prevalence of overweight/obesity and increased risk for heart disease, stroke, and type 2 (T-2) diabetes. The biological mechanisms underlying these related disorders are suggested to involve inflammatory pathways, changes in monoamine synthesis (serotonin), and greater insulin variability. Studies show that sedentary behaviors worsen some of these cardiometabolic risks, and we speculate that passive sedentary behaviors may have relatively larger negative impacts on these underlying processes. CHD, coronary heart disease; CRP, C-reactive protein; METS, metabolic syndrome; MVPA, moderate-to-vigorous physical activity.

What Are the Potential Implications for the Prevention and Treatment of Depression?

Structured exercise is an effective treatment for depression, with effect sizes equivalent to medication and psychological therapies (46). Additional health benefits, which may not be achieved through medication use alone, include improved physical fitness and cardiometabolic health. These somatic health benefits are highly relevant, as depression is associated with a premature mortality gap of approximately 10 yr, primarily due to preventable comorbid health conditions (1). Recognition of these significant health issues has instigated changes to national depression treatment guidelines, where physical activity is now receiving greater emphasis (47,48). Despite this progress, no intervention studies have examined the effects of targeted reductions in sedentary behavior (i.e., breaks in sitting or less total sitting) on mental health outcomes. Instead, trials have focused almost exclusively on exercise, whereas changes in sedentary behavior have either been overlooked or described as secondary findings.

Sedentary behavior interventions are feasible in diverse populations, including among adults with type 2 diabetes (49) and otherwise healthy office workers (50). These recent trials have demonstrated positive and clinically meaningful effects of interventions on health and well-being. Trials frequently involve multicomponent strategies targeting individual behavior, social support, environmental factors, policies, and attitudes. There is now potential to evaluate similar methods in trials involving psychiatric populations. Currently, the optimal type of intervention needed to prevent depression at the community level, or to treat depression clinically, is unclear. Reducing total sitting time and introducing active breaks in extended periods of sitting are shown to have positive effects on health (51), but the precise duration or combination of sedentary breaks and physical exercise needed to elicit meaningful changes in depression is unknown. Results from controlled trials using measures of diverse sedentary behaviors assessed in different contexts, particularly recreation and leisure, could lead to new treatment regimens in clinical settings targeting specific combinations of physical activity and breaks in sedentary behaviors. These findings could ultimately help optimize treatment outcomes and reduce relapse in depression.

CONCLUSIONS

It is now understood that in addition to the well-established health benefits of physical activity and exercise, sedentary behaviors can have deleterious effects on health and well-being, and this evidence has informed recent public health guidelines. Behaviors that affect somatic health can also impact mental well-being, and in recent years, sedentary behavior research has begun to address psychiatric outcomes. Sedentary behaviors can have detrimental impacts on depression, but findings are inconsistent, and research is limited mainly to observational studies of varying methodological quality.

Our recent findings have highlighted potentially important differences between passive and mentally active sedentary behaviors, where the former seem to increase the risk of depression, whereas the latter may protect against depression onset (31,32). This distinction, which is applicable primarily to leisure contexts, could partly explain the inconsistencies found in previous studies where mental health outcomes have been measured. Our findings require replication using objective measures of physical activity and sedentary time, but also suggest that a more systematic and refined approach to the assessment of these ubiquitous behaviors is needed. To facilitate this, we have suggested a framework for assessing diverse sedentary behaviors in the context of mental health research. Previous studies of sedentary behavior and cardiometabolic health have laid the foundation for advancing the understanding of links with mental health, but additional research is needed to progress the science and inform public health strategies with greater precision than currently possible.

Research Opportunities

Several countries, including Canada (52) and Australia (53), have incorporated physical activity recommendations into national treatment guidelines for depression. However, comparable emphasis currently is not given to sedentary behaviors, which generally are mentioned only with reference to reducing sedentary lifestyles. Recently, the European Psychiatric Association endorsed a position statement based on a review of the evidence for physical activity in serious mental illness (including depression) (48). One recommendation was that further research is needed to investigate the relative importance of reducing sedentary behaviors in the context of exercise interventions. With this goal in mind, we conclude by outlining seven specific areas of research that require greater development to advance current knowledge:

  • Prospective observational and experimental studies that help establish causal relationships between sedentary behavior and depression.
  • Observational studies that assess relationships of passive and mentally active sedentary behaviors in different contexts with depression.
  • Controlled trials investigating the interactions of physical activity, exercise, and sedentary behavior with depression, and the implications for treatment regimes in clinical practice.
  • Studies leading to the development and validation of new measures of diverse sedentary behaviors for use within mental health research and practice.
  • Research exploring relationships of passive and mentally active sedentary behaviors with cognitive functioning in those with depression.
  • Studies of the underlying psychosocial and biological mechanisms linking changes in sedentary behaviors with depression.
  • Studies of relationships between sedentary behavior, diet, and mood disorders also are needed.

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Keywords:

sedentary behavior; physical activity; exercise; depression; mental health; mechanisms; prevention

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