consequences increase as sleep restriction becomes chronic. Although several studies have shown increased risk of death is also associated with sleep duration of 9 hours or more, a clear explanation has not been presented for this, and attempts to shorten sleep lengths in otherwise normal long sleepers are not advised. There are significant individual differences in required sleep length so that incremental changes over time, such as those that may be due to aging, are not be pathological. However, changes in sleep requirement or daytime alertness can also be associated with many common medical conditions such as sleep apnea, diabetes, or thyroid dysfunction and should always be discussed with a physician.
Any discussion of sleep need that cannot explain why humans need sleep at all is not completely satisfying. Research suggests that sleep is a favored time for many types of restoration and renewal, but, as many systems benefit, there may not be a single sleep duration requirement even within an individual. Additionally, sleep that is frequently disturbed and therefore of poor quality cannot be evaluated by a simple duration number. Such caveats simply imply that sleep is a rich and still poorly understood phenomenon. However, current studies of the genetic composition of long and short sleepers and individuals more and less sensitive to sleep loss may allow better identification and stratification of groups to follow throughout life to understand outcomes more clearly. The genetic work may also provide associations with genes controlling other functions, and this might help to identify the specific role of sleep.
1. Kripke D, Simons R, Garfinkel L, Hammond E. Short and long sleep and sleeping pills: is increased mortality associated? Arch Gen Psychiat. 1979;36:103-16.
2. Bliwise DL, King AC, Harris RB, Haskell WL. Prevalence of self-reported poor sleep in a healthy population aged 50-65. Soc Sci Med. 1992;34(1):49-55.
3. Knutson KL, Van Cauter E, Rathouz PJ, DeLeire T, Lauderdale DS. Trends in the prevalence of short sleepers in the USA: 1975-2006. Sleep. 2010;33:37-45.
4. Luckhaupt SE, SangWoo T, Calvert GM. The prevalence of short sleep duriation by industry and occupation in the national