Adverse psychosocial working conditions and risk of severe depressive symptoms. Do effects differ by occupational grade?

BACKGROUND Depression is a major concern for public health. Both adverse working conditions and low socio-economic position are suspected to increase risk of depression. In a representative sample of the Danish workforce we investigated (i) whether adverse psychosocial working conditions, defined by the effort-reward imbalance (ERI) model, predicted onset of severe depressive symptoms after 5-year follow-up and (ii) whether the effect of ERI was differential across occupational grades. METHODS A cohort of 2701 Danish employees filled in a questionnaire on work and health in 2000 and 2005. ERI was measured with four effort and seven reward items. Depressive symptoms were assessed with the five-item Mental Health Inventory. Participants scoring ≤ 52 points were defined as cases. We used logistic regression to investigate the association of ERI and occupational grade in 2000 with onset of severe depressive symptoms in 2005. Analyses were adjusted for socio-demographics, health behaviours, survey method, self-rated health, sleep disturbances and non-severe depressive symptoms at baseline. RESULTS High ERI predicted onset of severe depressive symptoms at follow-up, after adjustment for co-variates and occupational grade (OR = 2.19, 95% CI = 1.12-4.25). Participants with high ERI and low occupational grade showed a considerably higher OR (2.43, 95% CI = 1.07-5.53) compared to participants with low/medium ERI and low grade (OR = 1.45, 95% CI = 0.72-2.92), high ERI and high grade (OR = 1.26, 95% CI = 0.59-2.70) and low/medium ERI and high grade (reference group). CONCLUSION Adverse psychosocial working conditions predicted onset of severe depressive symptoms. The effect was stronger among employees of lower occupational grades compared to those of higher grades.