Background Long working hours and unpaid work are possible risk factors for depressive symptoms. However, little is known about how working hours influence the course of depressive symptoms. This study examined the influence of paid, unpaid working hours and total working hours on depressive symptoms trajectories.

Methods The study was based on data from four waves of the Swedish Longitudinal Occupational Survey of Health (SLOSH 2008–2014). We applied group-based trajectory modelling in order to identify trajectories of depressive symptoms and studied paid and unpaid working hours and total working hours as risk factors.

Results Six trajectory groups were identified with symptoms: ‘very low stable’, ‘low stable’, ‘doubtful increasing’, ‘high decreasing’, ‘mild decreasing’ and ‘high stable’. More time spent on unpaid work was associated with the ‘low stable’ (OR 1.16, 95% CI 1.04 to 1.30) and the ‘high stable (OR 1.40, 95% CI 1.18 to 1.65) symptom trajectories compared with being in the ‘very low stable’ symptom group. In addition, more total working hours was associated with a higher probability of having ‘high decreasing’ (OR 1.30, 95% CI 1.14 to 1.48) and ‘high stable’ (OR 1.22, 95% CI 1.01 to 1.47) symptoms, when adjusting for sex, age, civil status and socioeconomic status. The results, however, differed somewhat for men and women. More unpaid working hours was more clearly associated with higher symptom trajectories among women. More total working hours was associated with ‘high stable’ symptoms among women only.

Conclusions This study supported heterogeneous individual patterns of depressive symptoms over time among the Swedish working population. The results also indicate that a higher burden of unpaid work and longer total working hours, which indicate a double burden from paid and unpaid work, may be associated with higher depressive symptom trajectories, especially among women.