Background Previous studies on changes in working conditions and mental health are few and have typically focused only on psychosocial working conditions. We assessed the impact of changes in both psychosocial and physical working conditions on common mental disorders (CMD) in a cohort of midlife employees.

Methods Repeat data were derived from the Helsinki Health Study, which is a cohort study on employees of the City of Helsinki, Finland (aged 40–60 years at baseline). Changes in working conditions were assessed between Phase 1 (2000–2002) and Phase 2 (2007). Common mental disorders were assessed at Phase 1, Phase 2, and Phase 3 (2012) using the 12-item General Health Questionnaire (GHQ). In total, 4946 participants were still employed at Phase 2. Logistic regression analyses using generalised estimating equations (GEE) were conducted to examine the association between changes in working conditions and the likelihood of CMD. Odds ratios and their 95% confidence intervals were estimated.

Results After adjustment for sex, age, marital status, health behaviours and obesity, increased and repeated exposure to low job control, high job demands, and repetitive movements; and repeated exposure to awkward postures and rotation of back were associated with a higher likelihood of CMD at Phases 1–3. Fully adjusted odds ratios ranged from 1.27 to 2.39 for psychosocial, and from 1.18 to 1.29 for physical working conditions.

Conclusion Repeated and increased exposures to several adverse psychosocial and physical working conditions are associated with a higher likelihood of common mental disorders.