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Letter to the Editor.

Dear Editor-in-Chief: We note the article by Schuch and Stubbs titled, “The Role of Physical Activity in the Prevention and Treatment of Depression,” recently featured in Current Sports Medicine Reports (1). This article is timely and presents a convincing evidence-based rationale for exercise prescription in those with depression. Here, we aim to complement their article, noting emerging evidence from studies of sedentary behavior and depression. Sedentary behavior (sitting/reclining) sits at the opposite end of the physical activity (PA) spectrum to moderate to vigorous activity, and is highly prevalent, with most Americans spending an estimated 12 h·d sedentary (2). High volumes of time spent sitting have been linked to increased risk of cardiovascular disease, type 2 diabetes, and all-cause mortality, and these associations are strongest in those who are the least physically active (3). Sedentary behavior is distinct from physical inactivity (i.e., <150 min of moderate to vigorous PA per week), and those with depression are substantially more sedentary than their nondepressed counterparts. Of importance, detrimental associations of sedentary behavior with depression have been reported. In a meta-analysis, the risk of depression attributable to sedentary behavior was 31% higher over 13 crosssectional studies, and 14% higher over 11 prospective studies (4). Inmost studies, adjustments for PAweremade, suggesting that these detrimental links are partly independent of PA levels. Two trials showed that experimentally induced sedentary behavior can have adverse effects on mood, depression, and inflammatory markers. Our own recent work indicates that, despite equivalent energy expenditures, sedentary behaviors that are passive in nature (e.g., TV viewing), and which mainly occur during leisure time, are more detrimental to depression than mentally active sedentary behaviors (e.g., office work, problem solving), which predominantly occur in occupational settings (5,6). Several mechanisms could explain these adverse relationships. Sedentary behaviors could displace time spent inmoderate to vigorous PA, and prolonged sedentary time frequently involves socially isolating activities which may remove people from supportive, mood-enhancing social interactions. Depression has been linked to higher levels of inflammatory markers, while an inverse association has been reported between PA and systemic inflammation. A review of 25 interventions found that acute bouts of uninterrupted sedentary behavior can result in deleterious changes in insulin sensitivity, glucose tolerance, and plasma triglyceride levels, which could indirectly affect mood and well-being (7). As sedentary behavior increasingly involves the use of screen-based devices, these activities also could contribute to sleep and mood disorders.