LONG SLEEP A GREATER MORTALITY RISK THAN SHORT SLEEP IN OLDER ADULTS

To the Editor: We commend Mesas and colleagues for their excellent article, ‘‘Sleep Duration and Mortality According to Health Status in Older Adults.’’ Although the sleep field and the popular literature has focused a great amount of attention on the risks of short sleep, Mesas and colleagues’ study is consistent with many other epidemiological studies that indicate that mortality and morbidity risks are even greater for long sleep. Moreover, as observed before, Mesas and colleagues found a greater prevalence of long than short sleep; the average respondent reported a sleep duration of 8 hour, which was associated with significant mortality, suggesting greater public health relevance of long than short sleep. Other strengths of the report are inclusion of a representative sample, consideration of combined nocturnal sleeping and daytime napping, and an extensive in-home interview with participants, which allowed moredefinitive assessment of reported sleep duration and other factors (e.g., current medication use) than is typical in similar studies. Notwithstanding rapidly accumulating evidence from perhaps 100 studies showing associations of long sleep with mortality and morbidity, discussion of similar studies has typically focused on the mortality and morbidity risks of short sleep while dismissing the association with long sleep as some sort of artifact. For example, it has been argued that the opposite direction of putative causality (morbidity causing long sleep) is likely to explain the associations of long sleep with mortality and morbidity. Contrary to this argument are findings that the associations of long sleep with mortality and morbidity are just as apparent after controlling for multiple morbidities. The Mesas study goes one step further in showing that the association with mortality is observed even in samples restricted to apparently healthy individuals at initial assessment. Moreover, recent research with long sleepers found equal tolerance of chronic sleep restriction in apparently healthy individuals and those with existing morbidities, for whom more adverse effects would be expected if morbidity were truly the cause of their long sleep. Rather, the participants almost unanimously reported a long history of long sleep, which presumably preceded their morbidity. Critics of the association between long sleep and mortality have also raised the concern that data are limited to self-reported sleep duration, but recent studies have shown similar associations between objectively recorded sleep duration, mortality, and morbidity. We agree with Mesas and colleagues that the risks of long sleep might be related to time in bed and poor sleep quality. Studies that have distinguished between time in bed and sleep duration have found similar risks associated with these variables. The authors caution that ‘‘21.3% of persons aged 60 and older in Spain sleep at least 10 hours per day.’’ Moreover, nearly two-thirds of the sample reported 8 hours or more of sleep, and 8 hours was associated with significant mortality. However, against the current zeitgeist that we are a sleep-deprived society, this point is far from the message that older adults commonly receive. The message they hear is that 8 hour of sleep is necessary for health and that they ought to be able to sleep that long. This fear might partly explain why older adults often spend more time in bed but sleep less than young adults. We know that excessive time in bed can lead to greater sleep fragmentation, which has been associated with morbidity in epidemiological studies and in studies involving experimental induction of fragmentation. The argument that long sleep (or long time in bed) could not possibly be harmful is becoming more difficult to justify. The Mesas and colleagues results point to a need for more randomized controlled trials of sleep restriction or extension in older adults.