Background. Major depression is a prevalent mental disorder in the general population, with a multi-factorial etiology. However, work stress as a risk factor for major depression has not been well studied.

Method. Using a longitudinal study design, this analysis investigated the association between the levels of work stress and major depressive episode(s) in the Canadian working population, aged 18 to 64 years. Data from the longitudinal cohort of the Canadian National Population Health Survey (NPHS) were used (n=6663). The NPHS participants who did not have major depressive episodes (MDE) at baseline (1994–1995 NPHS) were classified into four groups by the quartile values of the baseline work stress scores. The proportion of MDE of each group was calculated using the 1996–1997 NPHS data.

Results. The first three quartile groups had a similar risk of MDE. Those who had a work stress score above the 75th percentile had an elevated risk of MDE (7·1%). Using the 75th percentile as a cut-off, work stress was significantly associated with the risk of MDE in multivariate analysis (odds ratio=2·35, 95% confidence interval 1·54–3·77). Other factors associated with MDE in multivariate analysis included educational level, number of chronic medical illnesses and child and adulthood traumatic events. There was no evidence of effect modification between work stress and selected sociodemographic, clinical and psychosocial variables.

Conclusions. Work stress is an independent risk factor for the development of MDE in the working population. Strategies to improve working environment are needed to keep workers mentally healthy and productive.