Insomnia symptoms and mortality

Abstract

Introduction Insomnia symptoms are associated with several health outcomes such as somatic and mental health, sickness absence and disability retirement. However, studies on the association between insomnia symptoms and mortality are few and their results inconsistent. In some studies frequent symptoms are associated with higher mortality risk, some others have found no or even reverse associations. Our aim was to examine the association of insomnia symptoms with all-cause mortality among ageing employees. Materials and methods The Helsinki Health Study baseline questionnaire survey data on 40–60-year-old City of Helsinki employees were collected in 2000–2002 (response rate 67%). These data were linked with register data on mortality until the end of 2011 ( n = 188 deaths) for those with written consent for such linkages (74%; N = 6,464). Insomnia symptoms included difficulties initiating and maintaining sleep, and non-restorative sleep (none, occasional, i.e. 1–14 nights per month, and frequent, i.e. 15 + nights per month). Baseline covariates included age, sex, education, marital status, obesity, alcohol drinking, physical inactivity, and mental health. Cox regression analysis was used to calculate hazard ratios (HR) and their 95% confidence intervals (CI). Results At baseline, 21% of women and 17% of men reported frequent insomnia symptoms. The summary measure examining any insomnia symptoms was not associated with all-cause mortality among men or women. However, difficulties in initiating sleep were strongly associated with mortality among men (HR 4.46, 95% CI 2.03–9.77). After adjusting for all covariates, the association attenuated but remained (HR 2.78, 95% CI 1.19–6.48). No associations could be confirmed among women or for difficulties maintaining sleep and non-restorative sleep. Conclusion Difficulties initiating sleep were associated with mortality among men. Otherwise insomnia symptoms were unassociated with mortality. Studies need to examine insomnia symptoms separately, especially as they may have contrasting associations with mortality. Health care should emphasise early detection and prevention of insomnia symptoms, especially difficulties initiating sleep. Acknowledgements Funding from the Academy of Finland, Finnish Work Environment Fund and University of Helsinki.