Sitting and doing absolutely nothing is one of my favourite pastimes. Perhaps it’s a result of having small children, or maybe it’s just an otherwise busy lifestyle. But I do know I’m not alone in my love of doing zilch while consuming mindless TV; in 2019, Netflix reported 167.1 million subscribed users. That’s a lot of people willing to pay for the pleasure of being passively entertained while remaining largely inactive. Of course, there are those that watch screens while undertaking vigorous exercise, but this blog isn’t about them.

A reduction in physical activity has reliably been linked to an increased risk in depression for some time (Schuch etl al., 2018) and evidence has long-documented the benefits of exercise in the treatment of mood disorders (Cooney et al., 2013). There is known to be a relationship between sedentary behaviour and unfavourable mental health outcomes, but what is unclear is whether all kinds of sedentary behaviour have similarly harmful effects on mental health.

In their paper, Hallgren et al. (2019) define TV watching as a passive sedentary behaviour. They set out to ascertain the impact on depression of replacing this with either:

• Mentally active sedentary behaviour (e.g. sitting in a meeting, reading)
• Light physical activity (e.g. walking) or
• Moderate-to-vigorous physical activity (e.g. jogging, swimming).

Methods

Using data from the Swedish National March Cohort (Lagerros et al., 2017), after removal of incomplete or excluded data (e.g. those under 18 years at follow up, or with an ICD-classified primary diagnosis of mental illness before beginning of follow-up), Hallgren et al.’s final sample consisted of an impressive 22,534 adults. Two thirds of the sample were female and the mean age was 49.2 years (S.D. = 15.8).

Initial self-report questionnaires were completed in 1997 and depression was assessed in two ways: cross-sectional analyses using self-ratings (“how often do you feel sad, low spirited, depressed?”) on a four point Likert scale (“never”, “sometimes”, “often”, “always”) and prospective analyses where responses were linked to clinician-diagnosed incidents of Major Depressive Disorder (MDD) during a 13 year follow up, (up to December 31^st 2010). Diagnoses were made by a specialist clinician, usually a Psychiatrist or Clinical Psychologist.

Four categories of behavioural activity were assessed via self-report: passive sedentary behaviour, mentally active sedentary behaviour, light physical activity and moderate-to-vigorous physical activity. The researchers examined the relationship with depression of replacing passive sedentary behaviour with the same duration of mentally active sedentary behaviour, light physical activity and moderate-to-vigorous physical activity. A 30-minute slot was felt to be most appropriate and realistic duration for activities. Participants were asked to rate how much time they spent being physically active in a typical weekday and eight response categories were provided to record the time in minutes (e.g. 0-4 minutes, 5-8 minutes etc.). Answers were extrapolated to provide an average weekly duration of moderate to physical exercise and participants were categorised as either below, achieving or exceeding the World Health Organisation’s (2010) recommended periods of physical activity. The following covariates were included in analyses: BMI, education, smoking status, comorbid physical health conditions, age and gender.

Results

• Participants from the total sample of 22,534 reported approximately five and a half hours a day in total sedentary behaviour and 37 minutes a day in light physical activity and moderate to vigorous physical activity combined.
• At baseline, 6.3% of the total sample reported frequent symptoms of depression and over the 13-year follow up period, 1.7% were diagnosed with MDD.
• Of those who did not report depression at baseline, 1.4% developed MDD during the follow up period.
• Cross sectional modelling showed that replacing 30 minutes a day of passive sedentary behaviour with 30 minutes of mentally active sedentary behaviour, light physical activity and moderate to vigorous physical activity reduced the likelihood of depression symptoms occurring by 5%.
• Modelled prospectively, exchanging 30 minutes of passive sedentary behaviour with 30 minutes of mentally active sedentary behaviour reduced the risk of developing MDD by 5%.

Conclusions

The authors concluded that passive sedentary behaviours may increase the risk of depression in adults and that substituting completely passive sedentary behaviour (e.g. taking a bath, watching TV, listening to music) with mentally active sedentary behaviour (e.g. knitting, sitting in a meeting, office work), light physical activity (e.g. walking) and moderate to vigorous physical activity (e.g. jogging, swimming) may reduce the risk of depression symptoms occurring in adults.

Mentally active sedentary behaviour may function as a protective factor in that it could reduce the opportunity for negative thought processes. Moreover, physical activity is known to reduce stress hormones and increase positive neurological processes thought to influence and regulate mood in humans.

Strengths and limitations

• This is a valid and worthwhile piece of research that represents a strong contribution to the literature on behavioural activity levels and depression. The researchers have used advanced statistical methods to model both cross sectional and prospective findings and controlled for potential confounding variables such as weight, education and baseline physical health.
• Whilst this study benefits from a large and varied sample, much of the data relies on self-report ratings. Measures of depression were corroborated by clinician diagnoses at follow-up but assessment of activity level was reliant on accurate self-observation which is known to be subject to bias. However, objective ratings of this type of measure would be very difficult to obtain and inevitably lead to a much smaller, less statistically powerful sample.
• The researchers note a relatively low incidence of MDD amongst their sample and posit that this could be due to their diagnoses being obtained from specialist healthcare registers that might have missed milder cases of severe depression presenting to primary care.
• Differences in the effects of passive and mentally active sedentary behaviours on depression can be found in the context of listed activities; for example, office work and partaking in meetings were activities included in the current study’s category of mentally active sedentary behaviour, but statistical control of employment status was not achieved – it could be that simply being employed functioned as a protective factor against depression given that we know that employment is linked to improved mental health (Waddell and Burton, 2006).
• The researchers also note that some generalizability of their data is limited due to the changes in the way humans use technology since baseline data was collected in 1997 – smart phone and internet use as a sedentary behaviour is very common in 2020, but was not captured by the current study. Future replications could consider the introduction of this technology on human mentally passive and active sedentary behaviour.

Implications for practice

The cross sectional findings of this study are relevant from a prevention perspective; they could be good indicators of those likely to go on to develop MDD in future.

Importantly, this study provides evidence for the use of behavioural activation as an intervention in treatment for depression and suggests that treatment should include not only increasing light and moderate to vigorous physical activity, but also seek to replace passive sedentary behaviours with mentally active ones for the best possible chance of symptom improvement.

Statement of interests

None.

Links

Primary paper

Hallgren, M., Nguyen, T. T., Stubbs, B., Vancampfort, D., Lundin, A., Dunstan, D., Bellocco, R., and Lagerros, Y. T.^. (2019). Cross-sectional and Prospective Relationships of Passive and Mentally Active Sedentary Behaviours and Physical Activity With Depression. British Journal of Psychiatry, 21, 1-7. https://doi.org/10.1192/bjp.2019.60

Other references

Cooney, G. M., Dwan, K., Greig, C. A., Lawlor, D. A., Rimer, J., Waugh, F. R. et al. (2013). Exercise for depression. Cochrane Database of Systematic Reviews, 9. CD004366. https://www.cochranelibrary.com/cdsr/doi/10.1002/14651858.CD004366.pub6/abstract

Lagerros, Y. T., Hantikainen, E., Mariosa, D., Ye, W.M., Adami, H. O., Grotta, A., et al., (2017). Cohort profile: the Swedish National March Cohort. International Journal of Epidemiology, 46, 795. https://pubmed.ncbi.nlm.nih.gov/27649800/

Schuch, F. B., Vancampfort, D., Firth, J., Rosenblum, S., Ward, P.B., Silva, E.S. etl al. (2018).  Physical activity and incident depression: a meta-analysis of prospective cohort studies. American Journal of Psychiatry, 175, 631-648. https://pubmed.ncbi.nlm.nih.gov/29690792/

Waddell, G. and Burton, A. K. (2006). Is Work Good for Your Health and Wellbeing? (PDF) The Stationary Office.

World Health Organization (WHO, 2010). Global recommendations on physical activity for health: world health organization guidelines approved by the guidelines review committee. https://www.who.int/dietphysicalactivity/global-PA-recs-2010.pdf

Photo credits

• Photo by Kate Stone Matheson on Unsplash