Objective To examine the long-term effects of a stress management intervention (SMI) based on the effort–reward imbalance (ERI) model, on psychological and biological reactions to work stress.

Methods 174 lower or middle management employees (99% male) were randomly assigned to an intervention or a waiting control group. The programme comprised 24×45 min group sessions (2 full days followed by two 4×45 min sessions within the next 8 months) on individual work stress situations. The primary endpoint was perceived stress reactivity (Stress Reactivity Scale, SRS), while secondary endpoints were salivary cortisol and α-amylase, anxiety and depression, and ERI. Assessments were repeated in 154 participants 1 year later.

Results SRS score decreased in both groups. A two-factor ANOVA with repeated measures showed a significant time×group effect (F=5.932; p=0.016) with the greater reduction in the intervention group. For SRS, the effect size (Cohen's d) after 1 year was d=0.416 in the intervention and d=0.166 in the control group. α-Amylase as a measure of sympathetic nervous system activation, decreased more strongly in the intervention group (area under the daytime curve and daytime slope: time×group effect p=0.076 and p=0.075). No difference was observed for cortisol. For depression, anxiety and ERI, improvements were higher in the intervention group but did not reach statistical significance.

Conclusions SMI based on work stress theory, is effective in reducing perceived stress reactivity and sympathetic activation in lower and middle management employees. Other mental health parameters and ERI show a tendency towards improvement. These beneficial effects are present 1 year later.