Epidemiologic studies have consistently shown that sleeping >8 h per night is associated with increased mortality. Indeed, the most recent American Cancer Society data of 1.1 million respondents showed that sleeping longer than 7.5 h was associated with approximately 5% of the total mortality of the sample. The excess mortality was found even after controlling for 32 potentially confounding risk factors. Although epidemiologic data cannot prove that long sleep duration causes mortality, there is sufficient evidence to warrant future testing of the hypothesis that mild sleep restriction would decrease mortality in long sleepers. Sleep restriction might resemble dietary restriction as a potential aid to survival. Sleep restriction has several potential benefits besides possible enhanced survival. Acute sleep restriction can have dramatic antidepressant effects. Also, chronic sleep restriction is perhaps the most effective treatment for primary insomnia. Conversely, spending excessive time in bed can elicit daytime lethargy and exacerbate sleep fragmentation, resulting in a vicious cycle of further time in bed and further sleep fragmentation. Sleep restriction may be most beneficial for older adults, who tend to spend excessive time in bed and have more sleep fragmentation compared with young adults.
Copyright 2004 Elsevier Ltd.