Insomnia symptoms and mortality: a register-linked study among women and men from Finland, Norway and Lithuania

Evidence on the association between insomnia symptoms and mortality is limited and inconsistent. This study examined the association between insomnia symptoms and mortality in cohorts from three countries to show common and unique patterns. The Finnish cohort comprised 6605 employees of the City of Helsinki, aged 40-60 years at baseline in 2000-2002. The Norwegian cohort included 6236 participants from Western Norway, aged 40-45 years at baseline in 1997-1999. The Lithuanian cohort comprised 1602 participants from the City of Palanga, aged 35-74 years at baseline in 2003. Mortality data were derived from the Statistics Finland and Norwegian Cause of Death Registry until the end of 2012, and from the Lithuanian Regional Mortality Register until the end of 2013. Insomnia symptoms comprised difficulties initiating sleep, nocturnal awakenings, and waking up too early. Covariates were age, marital status, education, smoking, alcohol, physical inactivity, obesity, diabetes, cardiovascular diseases, depression, shift work, sleep duration, and self-rated health. Cox regression analysis was used. Frequent difficulties initiating sleep were associated with all-cause mortality among men after full adjustments in the Finnish (hazard ratio 2.51; 95% confidence interval 1.07-5.88) and Norwegian (hazard ratio 3.42; 95% confidence interval 1.03-11.35) cohorts. Among women and in Lithuania, insomnia symptoms were not statistically significantly associated with all-cause mortality after adjustments. In conclusion, difficulties initiating sleep were associated with mortality among Norwegian and Finnish men. Variation and heterogeneity in the association between insomnia symptoms and mortality highlights that further research needs to distinguish between men and women, specific symptoms and national contexts, and focus on more chronic insomnia.