Association Between Insomnia And Mortality Is Only Evident Among Long Sleepers

Abstract

Background

Previous studies investigating the relationship between insomnia and mortality have been inconsistent.

Purpose

We aimed to assess whether nocturnal insomnia symptoms and non-restorative sleep are associated with all-cause mortality and whether they modify the associations between short and long sleep duration and all-cause mortality.

Patients and methods

The present report is based on a prospective cohort study of 39,139 participants with a mean follow-up time of 19.6 years. Cox proportional hazard models with attained age as timescale were used to estimate overall mortality hazard ratios (HRs) with 95% confidence intervals (CI) for different categories of sleep duration and insomnia symptoms.

Results

Both difficulty initiating sleep and daytime sleepiness were independently associated with increased mortality among those with sleep duration of 9 hrs or more (HR 1.51, 95% CI 1.11–2.07 and HR 1.37, 95% CI 1.03–1.82). Mortality increased with increasing severity of difficulties initiating sleep (p for trend 0.04) and daytime sleepiness (p for trend 0.01) among the long sleepers. None of the insomnia symptoms were associated with mortality among those who reported sleep duration of 8 hrs or less.

Conclusion

Long sleep in combination with difficulties initiating sleep and daytime sleepiness, possibly due to psychiatric or physical disorders, was thus associated with increased mortality, whereas long sleep without difficulties falling asleep or daytime sleepiness was not associated with mortality. Our study emphasizes the need to take nocturnal insomnia symptoms and daytime sleepiness into consideration when assessing the influence of sleep duration on mortality. Additional research is needed to elucidate the relationship between long sleep, insomnia and related psychiatric and physical disorders.

Keywords:

• prospective cohort study
• sleep quality
• sleep duration

Author Contributions

All authors contributed to study concept and design. AKH performed the statistical analyses and drafted the manuscript. All authors interpreted the data and critically revised the manuscript, approved the final version of the manuscript, and agreed to be accountable for all aspects of the work. 

Disclosure

The authors report no conflicts of interest in this work.

Additional information

Funding

The study was supported by grants from the Swedish Society for Medical Research.