A considerable amount of research has shown that leisure time physical activity can be a protective factor against depression (Pearce et al., 2022); with the latter being a leading cause for disability globally (Ferrarelli, 2022). However, empirical evidence has highlighted occupational physical activity (OPA) – physical activity that is performed as part of one’s work duties – as a potential risk factor for depression and other health-related outcomes (Quinn et al., 2021), contributing to what is called as the “Physical Activity Paradox”.
So how can a protective factor become a risk factor, when occurring in the workplace? While the “how’s and why’s” of the potentially negative relationship between OPA and health-related outcomes have not been clearly explained, some characteristics of OPA, such as its mandatory nature, limited time for recovery and being a contributor to inflammation, have been part of suggested hypotheses (Holtermann et al., 2018).
However, OPA does not happen in a vacuum; this means that apart from the OPA-related consequences, several other stressors can be found in most work environments, which are in turn also associated with increased depressive symptoms. Thus, the researchers leading this study (Werneck et al., 2022) explored whether the presence of stressful workplace characteristics can lead to changes in the relationship between occupational physical activity and increased depressive symptoms among Brazilian working adults.
The authors conducted a secondary analysis of data from the 2013 Brazilian National Health Survey, a cross-sectional epidemiological study of a nationally representative sample of Brazilian adults. The sample comprised of 36,442 active workers (16,992 women) aged 18 and over. Participants were asked questions about:
- Demographic variables
- Depressive symptoms, using the Patient Health Questionnaire (PHQ-9) (score >10 indicated elevated depressive symptoms)
- Occupational physical activity (OPA), using the relevant section of the Surveillance System for Risk and Protective Factors for Chronic Diseases by Telephone Survey (VIGITEL) Questionnaire, with two cut-off points; highest quantile 600min/week for men, >0min/week for women; 150min/week based on previous study (Werneck et al., 2020)
- Stressful Workplace Characteristics (SWCs), using an adaptation of the Basic Questionnaire and Methodological Criteria for Surveys on Working Conditions, Employment and Health in Latin America and the Caribbean.
Logistic regression models and moderation analyses were used to analyse the relationships between OPA and SWCs, as well as with increased depressive symptoms, controlling for demographic data.
From the total sample, 6.8% reported elevated depressive symptoms (2,490 participants). Depressive symptoms were more prevalent in those who were/reported:
- Middle-aged adults
- Intermediary education level
- High OPA (occupational physical activity) for both cut-off points
- Exposed to SWCs (stressful workplace characteristics)
- Inactive at leisure time
- Tobacco smoking
- Increased TV viewing
- Regular/poor self-rated health.
Occupational physical activity (OPA) at both cut-off points was associated with increased depressive symptoms among both genders.
The relationship between higher OPA and elevated depressive symptoms did not change depending on the presence/absence of stressful workplace characteristics (SWCs).
SWCs were rather identified as confounders, as the relationship between OPA and elevated depressive symptoms was reduced when SWCs were included in the tested model.
When the cluster of participants that reported at least two SWCs was included in the tests, the association of OPA with elevated depressive was reduced for both men and women:
- Men (≥150 min/week: OR: 1.25; 95% CI: 0.95 to 1.64; highest quintile: OR: 1.36; 95% CI: 1.08 to 1.91)
- Women (≥150 min/week: OR: 1.80; 95% CI: 1.42 to 2.27; highest quintile: OR: 1.83; 95% CI: 1.47 to 2.29).
The authors concluded that stressful workplace characteristics (SWCs) are associated with both occupational physical activity (OPA) and elevated depressive symptoms; however, the relationship between OPA and elevated depressive symptoms was not explained by the presence/absence of the examined SWCs. SWCs acted as a confounder, leading the authors to hypothesise that the concomitant existence of OPA and SWCs might have contributed to an overestimation of the role of OPA in the elevated depressive symptoms. Thus, the SWCs might be contributing to the elevated depressive symptoms while being related to OPA as well, to the extent that OPA is not significantly related to elevated depressive symptoms among men when including SWCs, while the relationship is significantly weakened among women. The examined SWCs had a stronger effect among men, while women might be more vulnerable to SWCs as far as depressive symptoms are concerned.
Strengths and limitations
The authors identified the large nationally representative sample of Brazilian workers as one of the strengths of the study, as well as the use of two cut-off points for OPA, which increases the ability for comparisons with other studies. Also, it should be noted that the authors controlled for a considerable number of demographic characteristics and provided results stratified based on gender.
As far as the limitations are concerned, the authors identified the cross-sectional design and the potential recall-bias due to self-rated measures as the main limitations of the study. Given the data was originally collected in 2013, the events of the latest years – and specifically the changes in the work industry caused by the COVID-19 pandemic – cannot be accounted for. Moreover, while the PHQ-9 is a widely used and validated tool for screening depressive symptoms, it is based on diagnostic criteria for depression, which in clinical practice requires the mandatory presence of depressed mood and/or loss of interest and the exclusion of any symptoms attributable to any other medical condition rather than a score-based cut-off point.
Generalisability is also an issue, as the study was carried out only in Brazil, limiting the comparison to other populations and of course other countries. In addition, a limited number of SWCs was included, while most of them were related to the presence/absence of physical work-environment characteristics (e.g., noise, sun), while others might be limited to specific work-environments (e.g., exposure to radioactive materials). Moreover, the use of binary variables (Yes/No) for the SWCs, while clear for “objective” stressors (e.g., exposure to radioactive materials), is not the optimal for psychological stressors (e.g., exposure to stress). Only two psychological stressors were included in the study and those were open to individual interpretation; both workplace violence and exposure to stress are generic terms that would probably require better operationalisation or explanation to the participants.
It is also unclear to what extent some of these stressors might be relevant to predominantly “men’s/women’s” jobs, as this might also account for the gender differences identified in the study. Other specific work stressors that might be significant in some professional groups were omitted (e.g., delivering bad news to patients as a SWCs for healthcare professionals). It would have been nice to see some more information about the industries where the participants were employed at the time of data collection.
Implications for practice
The authors link the findings to potential implications relevant to interventions. In terms of occupational physical activity (OPA), the findings suggest that:
- OPA is related to elevated depressive symptoms and should be treated as a potentially harmful factor for employees’ health taking into account potential gender differences
- Addressing OPA-related problems, such as minimising the need for recovery and improving work conditions to make OPA more comfortable, can potentially help address the concomitant elevated depressive symptoms
- Future research on OPA should consider treating stressful workplace characteristics (SWCs) as a confounder rather than a moderator/or mediator
- Given its association with elevated depressive symptoms and with other health related outcomes shown in previous studies, OPA can potentially constitute a SWC which needs to be further explored.
Statement of interests
I have no competing interests to declare.
Werneck, A. O., Kandola, A., Barboza, L. L., Araujo, R. H., Szwarcwald, C. L., Stubbs, B., & Silva, D. R. (2022). Does stressful workplace characteristics moderate or confound the association between occupational physical activity and elevated depressive symptoms? A large study including 36,442 adults. Journal of affective disorders, 303, 196-202.
Ferrarelli, F. (2022). Is neuroplasticity key to treatment response in depression? Maybe so. American Journal of Psychiatry, 179(7), 451-453.
Holtermann, A., Krause, N., Van Der Beek, A. J., & Straker, L. (2018). The physical activity paradox: six reasons why occupational physical activity (OPA) does not confer the cardiovascular health benefits that leisure time physical activity does. British journal of sports medicine, 52(3), 149-150.
Quinn, T. D., Yorio, P. L., Smith, P. M., Seo, Y., Whitfield, G. P., & Gibbs, B. B. (2021). Occupational physical activity and cardiovascular disease in the United States. Occupational and Environmental Medicine, 78(10), 724-730.
Pearce, M., Garcia, L., Abbas, A., Strain, T., Schuch, F. B., Golubic, R., … & Woodcock, J. (2022). Association Between Physical Activity and Risk of Depression: A Systematic Review and Meta-analysis. JAMA psychiatry.