Long Sleep Duration, But Not Short Sleep Duration, Predicts Mortality Risk
The largest meta-analysis to date on sleep duration and mortality risk, involving 35 published studies and over 1.5 million adults, found that the increased risk of death associated with sleeping more than 7 hours was significantly greater than the risk of sleeping less than 7 hours. Regarding short sleep and mortality risk, previous studies using extreme definitions of short sleep duration of less than 5 hours per night have found associations with mortality but the magnitude of association is, at best, modest. Furthermore, there are an equal number of studies that have not found an association between short sleep and mortality (especially after accounting for inflammatory markers and other health factors).
Another study found that long sleep duration, but not short sleep duration, is associated with all cause mortality in middle-aged and older adults. The study, published in a 2016 issue of the journal Sleep, examined the relationship between sleep duration and mortality in a sample of over 5000 middle-aged and older adults. This study expanded on previous studies on sleep duration and mortality by accounting for sleep apnea as a potential confounding variable. The researchers controlled for numerous other potential confounding variables such as age, sex, smoking, weight, hypertension, diabetes, cardiovascular disease, and antidepressant medication use/depression.
The study involved three groups of subjects: those reporting less than 7 hours of sleep, those reporting 7-8 hours of sleep, and those reporting 9 or more hours of sleep. Sleeping less than 7 hours was defined as short sleep while sleeping 9 or more hours was defined as long sleep. The researchers also assessed changes in sleep duration and its relation to mortality by measuring sleep duration at baseline and at follow-up. The researchers found that, compared to 7-8 hours of sleep, sleeping 9 or more hours was associated with increased mortality risk while sleeping less than 7 hours was not. Furthermore, individuals who changed from short or normal sleep duration to long sleep duration had increased risk for all-cause mortality. Also, changing from 9 or more hours of sleep to less than 7 hours was also associated with increased mortality risk but progressing from 7-8 to less than 7 was not. These associations were not explained by health status or sleep apnea.
The authors concluded that the data do not support an association between short sleep and mortality risk in middle-aged and older adults but do support an association between long sleep and mortality in these age groups. They also concluded that long sleep is not due to sleep apnea or other health problems, and that the association between long sleep and mortality is not due to these health problems.