Clinical wisdom and supporting research suggest that most people require approximately eight hours of sleep nightly . However, there appears to be considerable variation around the mean, with many people claiming to need only four to six hours of sleep. The definition and consequences of sleep deprivation are reviewed here. Sleep deprivation is distinguished from insomnia separately (see "Overview of insomnia", section on 'Differential diagnosis').
DEFINITION OF SLEEP DEPRIVATION
Sleep deprivation exists when sleep is insufficient to support adequate alertness, performance, and health, either because of reduced total sleep time or fragmentation of sleep by brief arousals. Acute sleep deprivation refers to no sleep or a reduction in the usual total sleep time, usually lasting one or two days. In contrast, chronic sleep deprivation (also called sleep restriction) exists when the individual routinely sleeps less than required for optimal functioning.
More than one-third of individuals report sleeping less than seven hours per night on weekdays or workday nights, according to the 2005 to 2008 National Health and Nutrition Examination Survey . This was most common among individuals 20 to 59 years of age and among non-Hispanic blacks. Individuals who reported sleeping fewer than seven hours per night were more likely to report difficulty concentrating than individuals who reported sleeping seven to nine hours per night (29 versus 19 percent).
CAUSES OF SLEEP DEPRIVATION
Sleep deprivation may be a consequence of an insufficient amount of sleep and/or poor quality sleep.
Insufficient quantity of sleep — It is difficult to determine what constitutes a normal quantity of sleep for a given individual. One approach involves determining how long a patient would sleep if left to awaken spontaneously. An alternative approach involves determining how alert the patient feels after different durations of sleep. Alertness is normal if the patient wakes feeling refreshed and is capable of moving through the day feeling alert without effort, even when placed in boring or monotonous situations. This sense of easy alertness should be distinguished from alertness that exists when the individual feels pressure, since the latter may persist despite sleep deprivation.