White Paper: How Much Sleep Do Adults Need?
9 hours or more) (25), (26), (27). Two studies have also analyzed the responses to a second questionnaire about six years later and a follow up 17 - 22 years later to determine who had died and the relationship to sleep duration. People who consistently reported short and long sleep on both questionnaires still had increased mortality (26), (27). In both studies, individuals who initially slept for about 7-8 hours but had begun sleeping either less or more than this by the time they had completed the second questionnaire had an increase in mortality(27), (26). Of interest, individuals who increased their sleep length from short at the first observation to average at the second observation no longer had increased mortality at the end of the study period. Finally, individuals who decreased their sleep duration from long to 7-8 hours no longer had increased mortality (26).
As discussed earlier, numerous experimental studies have shown associations between short sleep durations and markers for diabetes, obesity, and hypertension. The presence of these common conditions is also associated with mortality. However, long sleep durations have not been associated with these medical problems (28). In a recent study that replicated the classic finding of increased risk of death for both short and long sleepers, the data were analyzed to consider the effect of age; and the increased risk associated with both short and long sleep durations disappeared in the younger individuals (ages 32 – 59) but not in older individuals (ages 60 - 86) (29). Further, it was found that the prevalence of both long and short sleep durations increased greatly in 70 and 80-year-old individuals (plotted in Figure 1). This suggests that changes in sleep duration were common starting only a few years before death and might reflect inflammatory processes or undiagnosed underlying medical or psychiatric problems in low socioeconomic individuals. For example, long sleep was strongly related to a history of depression or antidepressant or anti-anxiety medication use; a report of living alone or having fewer children; or the lack of employment or low social economic status (30). This implies that long