Objective: The purpose of this study is to prospectively examine the independent contribution of symptoms of insomnia on sick leave.
Methods: We used a historical cohort design with 4 years of follow-up. Information on sick leave was obtained from Norwegian official registry data and merged with health information from the Hordaland Health Study in Western Norway, 1997 to 1999. Six thousand eight hundred ninety-two participants aged 40 to 45 years were assessed for self-reported symptoms of insomnia, sociodemographic factors, lifestyle behaviors, body mass index, symptoms of sleep apnea, anxiety, depression, as well as a range of somatic diagnoses, somatic symptoms, and pain. The outcome was the total number of sick days during a 4-year follow-up period, as registered in the official registries by the National Insurance Administration.
Results: Overall, insomnia was found to be a significant predictor of sick leave [odds ratio (OR)=2.20; 95% confidence interval (CI), 1.77-2.74], and the effect remained significant when adjusting for possible confounders (OR=1.51; 95% CI, 1.19-1.94). The effect increased with longer durations of sickness leave.
Conclusion: This is the first study to demonstrate that insomnia is an independent risk factor for long-term sick leave.