Objective/background: Associations between exposure to effort-reward imbalance at work (eg, high time pressure/low appreciation) and risk of sleep disturbances have been reported, but the direction of the effect is unclear. The present study investigated changes in effort-reward imbalance and risk of concomitant and subsequent onset of sleep disturbances.

Methods: Participants with sleep disturbances at baseline were excluded. We included participants from a population-based cohort in Denmark (n = 8,464, 53.6% women, mean age = 46.6 years), with three repeated measurements (2012 (T0); 2014 (T1); 2016 (T2)). Changes in effort-reward imbalance (T0-T1) were categorized into 'increase', 'decrease' and 'no change'. Self-reported sleep disturbances (difficulties initiating or maintaining sleep, non-restorative sleep, daytime tiredness) were dichotomized (presence versus absence). We regressed concomitant (T1) and subsequent (T2) sleep disturbances on changes in effort-reward imbalance (T0-T1) and calculated odds ratios (OR) and 95% confidence intervals, adjusted for sex, age, education and cohabitation.

Results: At follow-up, 8.4% (T1) and 12.5% (T2) reported onset of sleep disturbances. Increased effort-reward imbalance was associated with concomitant sleep disturbances (T1) (OR = 3.16, 2.56-3.81), whereas decreased effort-reward imbalance was not (OR = 1.22, 0.91-1.63). There was no association between increased effort-reward imbalance and subsequent sleep disturbances (T2) (OR = 1.00, 0.74-1.37). Results were similar for men and women.

Conclusions: Increased effort-reward imbalance was associated with a three-fold higher risk of concomitant onset of sleep disturbances at two-year follow-up, but not subsequent onset of sleep disturbances at four-year follow-up, indicating that changes in effort-reward imbalance have immediate rather than delayed effects on sleep impairment. It is possible that the results from the two-year follow-up were to some extent affected by reverse causality.