Sleep Duration and All-Cause Mortality
Objectives: To assess whether the population longitudinal evidence supports the presence of a relationship between duration of sleep and all-cause mortality, to investigate both short and long sleep duration and to obtain an estimate of the risk.
Methods: We performed a systematic search of publications using MEDLINE (1966-2009), EMBASE (from 1980), the Cochrane Library, and manual searches without language restrictions. We included studies if they were prospective, had follow-up >3 years, had duration of sleep at baseline, and all-cause mortality prospectively. We extracted relative risks (RR) and 95% confidence intervals (CI) and pooled them using a random effect model. We carried out sensitivity analyses and assessed heterogeneity and publication bias.
Results: Overall, the 16 studies analyzed provided 27 independent cohort samples. They included 1,382,999 male and female participants (follow-up range 4 to 25 years), and 112,566 deaths. Sleep duration was assessed by questionnaire and outcome through death certification. In the pooled analysis, short duration of sleep was associated with a greater risk of death (RR: 1.12; 95% CI 1.06 to 1.18; P < 0. 01) with no evidence of publication bias (P = 0.74) but heterogeneity between studies (P = 0.02). Long duration of sleep was also associated with a greater risk of death (1.30; [1.22 to 1.38]; P < 0.0001) with no evidence of publication bias (P = 0.18) but significant heterogeneity between studies (P < 0.0001).
Conclusion: Both short and long duration of sleep are significant predictors of death in prospective population studies.
From press release:
Research carried out by the University of Warwick in collaboration with the Federico II University Medical School in Naples, Italy, has found that people who sleep for less than six hours each night were 12% more likely to die prematurely than those who get the recommended 6-8 hours.
The study, recently published in the journal Sleep, provides unequivocal evidence of the direct link between short duration of sleep (less than 6 hours sleep a night) and an increased chance of dying prematurely.
The research also notes that consistent over long sleeping (over 9 hours a night) can be a cause for concern. While, unlike short sleeping, over long sleeping does not in itself increase the risk of death, it can be a significant marker of an underlying serious and potentially fatal illnesses.
The study looked at the relationship between the level of habitual duration of sleep and mortality by reviewing 16 prospective studies from the UK, USA, European and East Asian countries. The study included more than 1.3 million participants, followed up for up to 25 years, with more than 100,000 deaths recorded.
The study provides unequivocal evidence of the direct link between both short (less than 6 hours sleep a night) and long (9 hours or more) duration of sleep and an increased chance of dying prematurely, compared to those who sleep 6-8 hours a night on average.
Professor Francesco Cappuccio, leader of the Sleep, Health and Society Programme at the University of Warwick and Consultant Physician at the University Hospitals Coventry and Warwickshire NHS Trust, said "whilst short sleep may represent a cause of ill-health, long sleep is believed to represent more an indicator of ill-health."
He said: "Modern society has seen a gradual reduction in the average amount of sleep people take, and this pattern is more common amongst full-time workers, suggesting that it may be due to societal pressures for longer working hours and more shift-work. On the other hand, the deterioration of our health status is often accompanied by an extension of our sleeping time.
"Consistently sleeping 6 to 8 hours per night may be optimal for health. The duration of sleep should be regarded as an additional behavioural risk factor, or risk marker, influenced by the environment and possibly amenable to change through both education and counselling as well as through measures of public health aimed at favourable modifications of the physical and working environments " Professor Cappuccio added.
Cappuccio FP, Elia L, Strazzullo P & Miller MA.
Sleep duration and all-cause mortality: a systematic review and meta-analysis of prospective studies.
University of Warwick and Federico II University Medical School in Naples, Italy.