How Much Sleep Do You Really Need?
Learn how much sleep is enough (or too much) and why you should care
Apr 20th, 2020 •
Sleep is more important than we like to believe, despite the fact that many of us feel we can “power through” periods of little to none of it.
We’ve all done it, whether it’s been studying for finals, long-distance travel, work deadlines, or that one time insomnia got the best of you.
Recent research, however, has shown just how dangerous and damaging insufficient sleep can be. A report by the National Sleep Foundation claims that getting on the road after 24 hours of sleeplessness results in similar performance as someone with a BAC of .10 – which is about one drink over the legal limit.
This is all in addition to the laundry list of harmful health effects of sleep deprivation such as increased risk of obesity and heart disease, reduced immune function and shorter life expectancy. Yeesh.
Settling your debt with the Sandman
As a general rule, the average adult needs around 8 hours of sleep a night, but in practice actually gets little more than 7-7.5 hours. However, it is very difficult to pin down what is optimal for any particular person, as individual sleep needs can vary quite significantly. Some people are just naturally “long sleepers” or “short sleepers”, and this does not constitute a sleep disorder of any sort, merely a genetic predilection, and daytime functioning in such individuals may be normal and healthy.
For example, some 6-10% of the adult population appears to need substantially more sleep than the average (9 or 10 hours or more a night), while about 5% can get by quite well on less than 6 hours a day. In a few extremely rare cases, as little as 3 hours may be enough for certain individuals to function without excessive daytime sleepiness or impaired performance. It should be noted that, although high achievers like Napoleon, Florence Nightingale, Louis XIV, Edison, Churchill and Margaret Thatcher are famous for sleeping short hours, others, like Einstein, for example, slept for 10 or even 12 hours a day (singer Mariah Carey claims to need 15 hours a day).
It is now clear that genetics regulates at least some aspects an individual’s sleep behaviour and requirements. The gene DEC2 is one gene that has been identified as specifically affecting sleep duration, and some people with a mutation of this gene may regularly sleep two hours less than the average. Some people with this mutation may need as little as 3 or 4 hours a night and still wake up feeling refreshed and alert. The gene ABCC9 is another gene that has been identified as affecting the duration of sleep, although more work remains to be done in this area. Because it is genetically programmed, there is therefore little we can do to “train” ourselves to need more or less hours of sleep.
What’s even worse is that the idea of sleep debt – the thought that we can “pay off” a few sleepless nights with extra sleep later on down the line – is just wishful thinking. The American Journal of Physiology published a study that revealed while “catch-up” sleep following a period of sleep deprivation helped reduce things like daytime fatigue and inflammation marker levels, it didn’t fix everything.
One of the most obvious side effects of sleep deprivation is difficulty paying attention throughout the day. Researchers found that attention problems present during the deprivation period continued into the recovery period. This consequence of sleep loss pays a large part of the $411 billion in productivity losses due to sleep deprivation that the US deals with each year.
Now that we’ve established just how important sleep is, how much of it do we actually need?
Using Sleep Measurement
Sleep time, the depth of sleep, and the various stages and cycles that make up sleep are best measured by means of polysomnography, which simultaneously measures several body functions such as brain activity (electroencephalogram or EEG), eye movement (electrooculogram or EOG), and skeletal muscle activity (electromyogram or EMG), as well as respiration, heart rhythm and a few other pertinent measures. The output from a polysomnograph is called a polysomnogram, an example of which is shown at right.
Polysomnograms are usually created as part of a personalized sleep study, often in a specialty sleep clinic or hospital. As part of such a study, it is also now common to videotape nighttime sleep activity in real time, to match against polysomnogram traces. Certain frequencies displayed by these measurements, and sometimes the relationships between them, are characteristic of the different stages of sleep or wakefulness the subject is in.
A hypnogram (see the example below) is a simplified graphical representation of the results obtained from a polysomnogram over a complete sleep period, presented in the form of a histogram or bar chart, and is a useful way of showing sleep cycles and the timing of the different sleep stages in an intuitive and easily visible way. The structure or pattern of sleep which emerges is often referred to as a person’s “sleep architecture”. Irregular sleeping patterns associated with various sleep disorders can often be detected in this way, as can the effects of certain medications or treatments.
A less invasive, but less accurate and reliable, method of sleep measurement involves a wrist-mounted unit called an actigraph, which essentially measures gross motor activity and movement, and which gives a rough and ready guide to sleep and wakefulness patterns. The output of an actigraph is called an actigram, and presents a simple graphical representation of a person’s sleep-wake cycle over several days, weeks or even months. This can be useful as a quick visual guide to the timing of sleep over an extended period.
Self-reported sleep patterns are quick, cheap and easy, but are usually considered unreliable, at least compared to these science-based measurements. This is especially so given the prevalence of “sleep state misperception” in which people typically under-estimate the length of time they sleep (and particularly over-estimate the time they take to fall asleep). It is not uncommon for someone to estimate, say, four hours of sleep when in fact they have slept for closer to seven or eight hours. Ingrained or chronic sleep state misperception may even be considered a type of sleep disorder. Specially designed questionnaires like the Epworth sleepiness scale can help to guide responses to some extent and make self-reported results more reliable, although they remain necessarily subjective.
Daytime sleepiness can be measured in two main ways: the multiple sleep latency test (MSLT), which measures the time needed to go from complete wakefulness to sleep onset in a series of daytime nap opportunities; and the maintenance of wakefulness test (MWT), which measures an individual’s ability to stay awake while reclining in a quiet darkened room.
Your optimal sleep duration, in handy-dandy chart form
The National Sleep Foundation recently released revised guidelines for how much sleep we need. In an update of their previous guidelines, the NSF added two new age categories, updated their sleep duration ranges and added a “may be appropriate” section in addition to the “recommended” hours.
Younger children tend to a have a much higher arousal threshold, and can sleep through even quite loud noises, which helps them to achieve the long sleep periods they need. A newborn baby may need anywhere from 12 to as many as 18 hours of sleep a day. For social and cultural reasons (as well as physiological reasons – see below) teenagers and young adults typically sleep substantially less than optimal amounts, and as many as a quarter of all college students are chronically sleep deprived. Shift workers, doctors, truck drivers and young parents are also at particular risk of sleep deprivation. Contrary to popular belief, the elderly actually need just as much sleep as younger adults, but they usually find this difficult to achieve (for a variety of reasons including the side-effects of medications, pain-related medical conditions, respiratory problems, etc, all of which are more common in older people), and their night sleep is typically lighter, shorter and more fragmented, often driving them to resort to afternoon naps.
See below for the recommended hours of sleep for each age category.
Required sleep by age
|Age||Recommended||May be appropriate||Not recommended|
|14 to 17 hours||11 to 13 hours
18 to 19 hours
|Less than 11 hours
More than 19 hours
|12 to 15 hours||10 to 11 hours
16 to 18 hours
|Less than 10 hours
More than 18 hours
|11 to 14 hours||9 to 10 hours
15 to 16 hours
|Less than 9 hours
More than 16 hours
|10 to 13 hours||8 to 9 hours
|Less than 8 hours
More than 14 hours
|9 to 11 hours||7 to 8 hours
|Less than 7 hours
More than 12 hours
|8 to 10 hours||7 hours
|Less than 7 hours
More than 11 hours
|7 to 9 hours||6 hours
10 to 11 hours
|Less than 6 hours
More than 11 hours
|7 to 9 hours||6 hours
|Less than 6 hours
More than 10 hours
≥ 65 years
|7 to 8 hours||5 to 6 hours
|Less than 5 hours
More than 9 hours
The timing of sleep is another aspect that changes as we age (see diagram below). Newborn babies do not yet have fully functional circadian clocks, and the sleep of newborns is typically split up into 3 or 4 hour periods throughout the day and night (polyphasic sleep), mainly dictated by the need to feed. As they get older, a longer sleep period during the night emerges, combined with one or two naps during the day. Ultimately, the daytime naps are not needed, and a normal nighttime sleep regime is established.
During adolescence and the teenage years, there is usually an unexplained phase delay of at least an hour or two, so that teens naturally feel more alert later at night and find it difficult to wake up early. Typically, they may not be ready for sleep until 11pm or 12pm, and not ready to wake again until around 9am, which clearly does not fit well with the usual regime of parental rules and school hours. Given this, it is perhaps not surprising that many teenagers are prone to mood and behaviour difficulties – sometimes misdiagnosed as attention deficit hyperactivity disorder (ADHD) – and it has been shown that even a modest delay in school start times can allow teenagers a more natural sleep profile, and can significantly improve both academic performance and behaviour.
After the age of about 55, the pendulum swings back the other way and older people are subject to a phase advance, and tend to be ready to sleep earlier in the evening and wake earlier in the morning.
While getting too little sleep may come with its obvious issues, getting too much sleep can be bad for your health too. A study with 400,000 participants revealed that people who slept more than eight hours and less than four hours each night carried the same risk of coronary heart disease (CHD).
So as long as I get my recommended hours of sleep I’m fine, right?
Well, maybe not.
Research suggests that sleep duration isn’t the only thing that determines how you feel during your waking hours. A regular sleep schedule is extremely important as well.
Harvard researchers have shown that there is a direct correlation between sleep regularity and GPAs in college students, debunking the idea of late nights in the library as something normal or healthy.
Okay, and what if I’m having trouble with all this?
If you’re aiming for that magic eight hours and can’t manage to either fall asleep on time or stay asleep, check out these tips for sleeping better.
Things like reducing caffeine intake, avoiding substances like alcohol or nicotine before bed, setting up a relaxing bedtime routine, and powering down before bed can all have a positive effect on your ability to fall asleep and sleep deeply without interruption.