Popular belief holds that adults should ideally get eight hours of sleep each night. But who came up with this number and how did they figure it out? Can one make the assumption that all adults have the same requirements for sleep? And to what degree does performance suffer if one cannot get all the shut-eye that their body needs?
One commonly cited source for the eight-hours-a-night prescription is the 2002 “Sleep in America Poll” that was sponsored by the National Sleep Foundation. In it, a third of respondents answered that they needed to snooze for a minimum of eight hours a night to not feel sleepy the following day.
Other evidence for designating eight hours of sleep as optimal comes from research studies in which healthy participants were required to remain in bed for a minimum of 14 hours day for more than a week. At first the majority of participants slept around 12 hours a day. But after acclimating to their new schedule, most of the subjects settled into a regular rhythm of sleeping between seven and nine hours a night. This would seemingly indicate that given the chance, most people would prefer to sleep around eight hours a night.
Still, some researchers have argued that the supposed basic sleep requirements are much lower than eight hours per night. In 1995 two researchers, Harrison and Horne, published an analysis entitled Should We be Taking More Sleep? which led to them to the conclusion that previous experiments into determining the basic daily sleep requirements had been flawed and/or misinterpreted. To this end the pair of researchers cited previous studies that had found that animals slept for other reasons besides physiological need and that increasing sleep produced only very tiny improvements in performance.
Studying the issue of the eight-hours-a-night rule requires making the important distinction between an individual’s basal sleep need and their sleep debt. The term “basal sleep need” refers to the amount of sleep a body regularly needs to perform optimally. When this basal sleep need is not met, a sleep debt is acquired. Understanding the need for sleep can be very difficult to untangle based upon the interactions of these two parameters. For example, a person who meets their basal sleep need for several nights in a row may still feel tired during the day because of a previously acquired sleep debt. In addition, some people may naturally have dips in their wakefulness based upon their circadian rhythm.
In fact, far from everyone requiring eight hours of shut-eye a night, according to the National Sleep Foundation website “there is no ‘magic number’” when it comes to determining how many hours of sleep an individual regularly needs. Rather, sleep needs can be thought of as existing on a spectrum, with the majority of people requiring somewhere between six and ten hours night (though there are exceptions). Establishing individual needs requires accounting for factors such as individual activity levels, dependence on stimulants, schedule, and of course the subjective feelings of tiredness.
By Sarah Takushi
American Psychological Association
2002 Sleep in America Poll
National Sleep Foundation