Exposure to high emotional, quantitative and physical job demands. Is there a synergistic effect on risk of depressive disorder?

OBJECTIVE: We examined prospective associations between three combinations of psychosocial and physical job demands and onset of depressive disorder and whether the combined effects of these demands exceeded what would be expected from their individual contributions (i.e. synergy, measured as departure from additivity). METHODS: We used data from the 2012, 2014, 2016, and 2018 wave of the Work Environment and Health in Denmark study, including 18,860 employees without depressive disorder at baseline. Onset of depressive disorder at follow-up was assessed using the Major Depression Inventory (MDI; score ≥21). Exposures were high emotional demands, high quantitative demands, and high physical job demands, combined into three two-pair combinations. Prospective associations with depressive disorder were estimated as odds ratios (OR) and 95% confidence intervals (CI) adjusted for age, sex, education, job group, and cohort using logistic regression models. Additive interaction was assessed by the relative excess risk due to interaction (RERI). RESULTS: Across all three combinations, combined exposure was consistently associated with the highest odds of onset of depressive disorder compared with the unexposed reference groups. The strongest association was observed for the combination of high quantitative and high physical job demands (OR 2.64; 95% CI 2.17 to 3.22), while the combination of high emotional demands and high quantitative demands showed a synergistic interaction beyond additivity (RERI 0.47; 95% CI 0.11 to 0.83). CONCLUSION: Simultaneous exposure to multiple psychosocial and/or physical job demands was associated with higher odds of onset of depressive disorder, with the combination of high emotional and high quantitative demands reflecting synergy beyond additivity.