It has been suggested that the correlation between lower sleep hours and reduced morbidity only occurs with those who wake naturally, rather than those who use an alarm.
Other studies show that "sleeping more than 7 to 8 hours per day has been consistently associated with increased mortality," though this study suggests the cause is probably other factors such as depression and socioeconomic status, which would correlate statistically.
Other studies show that "sleeping more than 7 to 8 hours per day has been consistently associated with increased mortality," though this study suggests the cause is probably other factors such as depression and socioeconomic status, which would correlate statistically.
Other studies show that "sleeping more than 7 to 8 hours per day has been consistently associated with increased mortality," though this study suggests the cause is probably other factors such as depression and socioeconomic status, which would correlate statistically.
Researchers at the University of Warwick and University College London have found that lack of sleep can more than double the risk of death from cardiovascular disease, but that too much sleep can also be associated with a doubling of the risk of death, though not primarily from cardiovascular disease
Other studies show that "sleeping more than 7 to 8 hours per day has been consistently associated with increased mortality," though this study suggests the cause is probably other factors such as depression and socioeconomic status, which would correlate statistically.
A University of California, San Diego psychiatry study of more than one million adults found that people who live the longest self-report sleeping for six to seven hours each night.[24] Another study of sleep duration and mortality risk in women showed similar results.
Human sleep needs can vary by age and among individuals, and sleep is considered to be adequate when there is no daytime sleepiness or dysfunction. Moreover, self-reported sleep duration is only moderately correlated with actual sleep time as measured by actigraphy,[22] and those affected with sleep state misperception may typically report having slept only four hours despite having slept a full eight hours.
The optimal amount of sleep is not a meaningful concept unless the timing of that sleep is seen in relation to an individual's circadian rhythms. A person's major sleep episode is relatively inefficient and inadequate when it occurs at the "wrong" time of day; one should be asleep at least six hours before the lowest body temperature.[20] The timing is correct when the following two circadian markers occur after the middle of the sleep episode and before awakening:
maximum concentration of the hormone melatonin, and
minimum core body temperature.
Sleep offset (awakening) is primarily determined by circadian rhythm. A person who regularly awakens at an early hour will generally not be able to sleep much later than his or her normal waking time, even if moderately sleep-deprived.
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