Sleep duration and mortality: A systematic review and meta-analysis

Conventional wisdom suggests that human beings require seven to eight hours of sleep a night to rest sufficiently. Factors such as lifestyle and sleep disorders can negatively impact the duration of sleep, and such imbalances can have significant implications on health and mortality.

A 2009 metastudy published in the Journal of Sleep Research, “Sleep Duration and Mortality: A Systematic Review and Meta-Analysis,” is a meta-study of results from 23 research papers documenting the relationship between sleep duration and mortality.

The study’s findings include:

• People who slept for longer durations (more than 10 hours per night) or shorter durations (fewer than five hours per night) had a greater risk of dying earlier compared to those who slept for medium duration (between seven and eight hours per night).
• The relative risk of all-cause mortality associated with shorter sleep duration is 1.1, while it is higher for longer sleep duration at 1.23. (Relative risk measures the risk of an event relative to exposure.)
• For both shorter- and longer-duration sleepers, there is no significant difference in risk between males and females.

The authors highlight the difficulty of pinpointing the precise number of hours of sleep associated with higher mortality risk because most accounts were self-reported.  In addition, the causal relationship between abnormal sleep lengths leading to the higher death risks is not necessarily straightforward, the researchers note, as the subjects could have some pre-existing health conditions or habits that led them to sleep longer.

Keywords: metastudy, sleep