Some sitting activities may be more harmful than others. A new study suggests that mentally-passive sedentary behavior such as watching TV may increase the risk of developing depression, while mentally-active sedentary behavior such as sitting at work does not have the same effect. Published in the Journal of Affective Disorders, the research also provides new insights into how waist size and inflammation may partly explain the link between mentally-passive sedentary behavior and depression.
Sedentary behavior refers to the time spent awake and sitting, reclining or lying, with low energy expenditure. Some activities include watching movies, reading, or driving. Researchers have observed that less mentally-demanding activity during sedentary behavior is linked to a higher risk of depression.
However the study team, led by André Werneck from the University of São Paulo in Brazil, aimed to delve further into potential mechanisms, or mediators, that explain how sedentary behavior and depression are associated. In particular, reduced sedentary behavior levels have been associated with lower inflammation, blood sugar levels, and body fat.
Werneck and colleagues hence sought to examine these biological mediators in relation to sedentary behavior and depression. These included measurements of C-reactive protein (produced by the liver when there is inflammation in the body), glycated hemoglobin levels (indicative of sugar levels in the blood), and also weight circumference.
Data was collected from the 1958 National Child Development Study, a study in the United Kingdom of individuals born in a specific week of 1958. A total of 4607 participants were analyzed, 2320 of whom were women.
Participants reported time spent in TV viewing (mentally-passive sedentary behavior) and sitting during work or driving (mentally-active sedentary behavior) at age 44. Waist circumference, C-reactive protein, and glycated hemoglobin were also measured at age 44. Depression diagnosis was self-reported at ages 44, 46, 50, and 55.
Following data analyses, the researchers discovered that mentally-passive sedentary behavior was associated with 43% higher risk of depression, while mentally-active sedentary behavior was not associated with incident depression.
Waist circumference (9.2%) and C-reactive protein (8.3%) partly explained the association of mentally-passive sedentary behavior with depression, suggesting that activities like TV viewing may increase depression risk by promoting obesity and inflammation. On the other hand, glycated hemoglobin did not mediate this relationship, indicating that blood glucose may not play a role in this context.
“While physical activity guidelines recommend reducing and breaking up sedentary time, our findings suggest that recommendations specific to mental health could emphasize reducing mentally-passive sedentary time.”
“Our findings also suggest that those at risk for depression and with high levels of mentally-passive sedentary behaviors could benefit from assistance to reduce waist circumference and C-reactive protein via increased levels of physical activity,” the authors concluded.
Some limitations are to be recognized. For example, sedentary behavior and depression were self-reported, leading to potential bias and underestimation. Additionally, due to technological advances since 2002 (when the first measurements were taken at 44 years of age), patterns of sedentary behavior in the workplace and leisure may have changed, and findings may be different in today’s age.
The study, “Mentally-passive sedentary behavior and incident depression: Mediation by inflammatory markers,” was authored by André O. Werneck, Neville Owen, Raphael H. O. Araujo, Danilo R. Silva, and Mats Hallgren.