Joint association of sleep problems and psychosocial working conditions with registered long-term sickness absence. A Danish cohort study

Objectives: Sleep problems and adverse psychosocial working conditions are associated with increased risk of long-term sickness absence. Because sleep problems affect role functioning they may also exacerbate any effects of psychosocial working conditions and vice versa. We examined whether sleep problems and psychosocial working conditions interact in their associations with long-term sickness absence. Methods: We linked questionnaire-data from participants to two surveys of random samples of the Danish working population (n= 10,752) with registry data on long-term sick leave during 5 years after questionnaire response. We defined sleep problems by self-reported symptoms and/or register data on purchases of hypnotic medications. Psychosocial working conditions included quantitative and emotional demands, influence, supervisor recognition and social support, leadership quality, and social support from colleagues. Using time-to-event models we calculated hazard ratios (HR) and differences and examined interaction as departure from multiplicativity and additivity. Results: During 40,165 person years of follow up we identified 2,354 episodes of long-terms sickness absence. Sleep problems predicted risk of long-term sickness absence (HR=1.56, 95%CI=1.40-1.75). This association was statistically significantly exacerbated in participants also exposed to high quantitative demands and buffered for those with high supervisor recognition (P=<0. 0001). Conclusions: High quantitative demands exacerbated the association of sleep problems with risk of long-term sickness absence whereas high supervisor recognition buffered this association. To prevent long-term sickness absence in employees with sleep problems, workplace modifications focusing on quantitative demands and supervisor recognition may be considered, and intervening on these factors may more effectively prevent long-term sickness absence when targeted towards employees with sleep problems. The effectiveness of such interventions needs established in future studies.