Recent experiments in sleep study have shown that napping may in fact do much more than just relieve fatigue.
Evidence suggests that with strategically timed naps, subjects have shown increases in many aspects of brain function when compared with subjects who didn't take naps (not just when compared with sleep-deprived people!).
Many scientists believe that the hour of increased fatigue that generally occurs between noon and 3pm for most people may in fact be a biological reaction to not taking an afternoon nap. We fall asleep naturally when we're tired in the evening, so why do we fight fatigue, and our natural circadian rhythms, in the early afternoon? The midafternoon siesta was a very common practice throughout Europe for centuries, and though it continues in some parts of Spain, it has unfortunately fallen out of practice for the rest of Europe and the world. If you ever feel fatigued throughout the day, this may help renew your energy!
Sleep homeostasis, or the biological urge to sleep, is controlled by our brain as part of our circadian rhythm, our bodies' natural "biological clock" that makes sure many of your bodily functions occur the same from day to day.
The "clock" is regulated in the portion of the brain called the SCN (suprachiasmatic nuclei), and research has shown that in animals who've had this portion of the brain removed, sleep occurs sporadically throughout the day, and is incredibly inefficient--the subjects will sleep in 5 minute bursts dozens and dozens of times per day, totaling in much more than normal time spent asleep (with the SCN intact), but also maintain a continuous level of extreme fatigue. The conclusion then is that our circadian rhythm not only compels us to sleep at the same time each day, but it also "compacts" the amount of time we need to sleep--we sleep for less time but more efficiently than we would if we didn't have it.
Why, then, should we nap if we already get all the sleep we need at night? The answer, according to some researchers, is that we just weren't designed to get all of our rest at night. Many animals sleep more than once per day, such as a house cat, which takes naps throughout the entire 24 hour day. This type of sleep schedule is called polyphasic sleeping. The tired stretch in humans that occurs between the hours of noon and 3pm is considered by some scientists to be strong anecdotal evidence suggesting that that we are not monophasic sleepers as most currently believe, but instead are biphasic. In other words, we're fatigued around noon because that's when it's natural for us to be asleep. (See this BBC article for evidence of our history of biphasic sleeping during the night.)
For most people, naps are a means of ridding oneself of excess sleep debt that might have accrued throughout the course of the day. Using napping as a tool to reduce sleep debt is a great idea, and something that everyone should do if their schedule permits it. However, the benefits of efficient napping go far beyond just relieving fatigue. In a study that had patients take a written test for which they had to exercise their hippocampus (the part of the brain that handles memory management), it was found that subjects who took a 15-20 minute nap in the middle of the day scored 30-40% higher on average than those who took no nap. Link: [See Study Here] Moreover, the effects are long lasting: in another study where subjects took 45 minute naps instead, they showed improved alertness for 6 hours compared with those who took no nap. Likewise, a one hour nap resulted in 10 hours of increased energy! [Stanford Sleep Book]
Often, people who take naps on a regular basis say that after the nap they feel rejuvenated, energized, and sharper. While this is very subjective, what can be proven is that sleep in the middle of the day will more often than not raise one's alertness levels, which can be determined by an MSLT reading. Moreover, if you time your nap to coincide directly with your "afternoon dip", you will be replacing the least productive (and most dangerous) part of your day with a nap that will rejuvenate you and make the rest of your whole day better. A Harvard School of Public Health study in 2007 conducted over a 6 year period with 24,000 men and women found that a short nap in early afternoon can reduce the risk of heart disease by 34%. [See Harvard Study]
In another study done by NASA on flight crews, when subjects were required to take a 40-minute nap, they showed 16% improvement in reaction time, 34% decrease in lapses of awareness, and briefly dozed off at the wheel only one quarter as often as those with no naps. [NASA Study]
As a result of the lessened fatigue you'll have, your overall mood for the rest of the day would increase, as would your problem-solving capabilities, it'd reduce your stress-load, improve your energy, reduce your risk of accidents, and the list goes on (quite literally--see the article on sleep deprivation if you're curious).
These benefits vastly outweigh any negative stigma napping may have! Just 15 minutes spent napping could very well save your life!
There are a lot of conflicting opinions on when is the best time for napping, or for how long you should nap, but it will depend more on what fits with your schedule than anything. The two main schools of thought are quick "power naps", or a longer "siesta nap".
Deep slow-wave sleep, the type of sleep you want to avoid waking up from a nap in, is NREM sleep stages 3 & 4. The body typically enters sleep in NREM stage 1, then quickly transitions to NREM stage 2, where it stays for a bit before proceeding to the deep stages 3 & 4.
A "power nap" would last about 15-25 minutes, with no longer than 40 minutes. The brief duration is important to prevent the body from entering into deep sleep. It's relatively easy to wake up and resume activity after a 15-25 minute long nap, but if you've entered deep sleep, it will be difficult to awaken, and you'll be very groggy and confused immediately upon waking due to sleep inertia. The idea of a power nap is it's enough to rejuvenate your body, which will give you a little extra boost throughout the day.
It's difficult to say how much sleep debt could be erased by a power nap, but most evidence would say you could only remove as much debt as you slept (so a 15 minute nap would remove 15 minutes' worth of sleep debt), though this idea is refuted by proponents of polyphasic sleep (discussed below). However, more subjects reported feeling better after a 10 minute nap than a 30 minute one, suggesting that the grogginess could really outweigh the positive effects of the nap for certain people. A power nap would have little to no effect on how long you should sleep at night.
In contrast, "siesta naps", which last somewhere around 90-120 minutes (again to time awakening in a stage other than deep sleep), are based on an entirely different concept. Their idea is to actually go through an entire sleep cycle, thus relieving a significant amount of sleep debt, and enabling the sleeper to sleep less than they normally would at night. One could, for instance, instead of sleeping 8 hours at night, sleep 6 hours at night and 2 in the afternoon. Most researchers agree you shouldn't nap for more than 4 hours for risk of dramatically upsetting your circadian rhythm. It would be harder to wake up from a longer nap, but depending on the person (how quickly they get over grogginess or how much time they have to spend napping in the middle of the day) the benefits might outweigh the costs.
Most literature agrees that napping during the "afternoon dip" is the best strategy, but many say that napping at any point in the day is better than not napping at all. If you sleep for too long, too late in the day, it will hinder your ability to actually fall asleep at night.
If one continues to take naps of relatively similar lengths at similar times of the day, many scientists believe that the circadian rhythm will actually shift and adapt to include these naps as part of its schedule. There is definite evidence that if humans are placed in darkness (without any artificial light) for 14 hours per day, their circadian rhythms change to a completely biphasic sleep schedule. Biphasic sleep is when a sleeper has two distinct sleep periods per day (and polyphasic is more than two per day). In the case of 14 hours of darkness, the subjects slept for two completely equal periods of sleep, each about 3.5 hours long. In a normal environment however, it is still possible to become "biphasic", if your circadian rhythm adjusts to include your nap as part of its schedule.[Study on Biphasic Sleeping]
There is a school of thought that biphasic sleep results in a net decrease of required sleep. There are some that believe that taking, for instance, a 2 hour nap in the afternoon plus 4 hours of sleep at night would give you an equivalent amount of energy and alertness as sleeping 8 hours at night. There exists much anecdotal evidence of this claim in the form of vlogs and blogs on the internet of people who've tried this and say it's true, however, there is no scientific evidence to back this up, and in fact, most current scientific beliefs refute this claim. Almost all research done on sleep debt indicates that it is transferred at a constant rate, and the concept could not be "cheated" in any way- 8 hours of sleep is 8 hours of sleep. If you're interested in potentially trying to "cheat" sleep in this way, read Dr. Wozniak's analysis of polyphasic sleep [Wozniak's Analysis], where he debunks many of the polyphasic myths you might observe on YouTube [Polyphasic Sleep Vlog] or elsewhere.
On the other hand, Winston Churchill adopted a biphasic sleep schedule for all of WWII, sleeping 2 hours in the day and 5 at night, and as a result was incredibly alert at all hours in the day, and could stay up later than most people, instead of getting progressively more fatigued throughout the day. It's unlikely that he was actually getting less sleep than he would have if he'd been a monophasic sleeper, as 7 hours per night is completely normal for some people, but since he "rejuvenated" for more hours of the day, he was well-known for being unnaturally energetic. He said on the subject:
"You must sleep sometime between lunch and dinner, and no halfway measures. Take off your clothes and get into bed. That's what I always do. Don't think you will be doing less work because you sleep during the day. That's a foolish notion held by people who have no imaginations. You will be able to accomplish more. You get two days in one -- well, at least one and a half"
And join the conversation with your own comments here:blog comments powered by Disqus
Welcome! This site is continuously being created by students of Dr. William C. Dement's Sleep And Dreams course at Stanford University.
We made this site as a call to action for people all over the world to live healthier, happier, safer, and more productive lives by learning about their own sleep. We have faith that reading the information provided on this site will motivate you to be smart about your sleep deprivation and strategic about your alertness in order to live life to your fullest, most energetic potential.
In fact, we challenge you to do so! What do you say, are you up for the challenge?
Dr. Dement's pioneering textbook has been the core text for Sleep and Dreams since 1980, but it has just recently been made available to the wider public for the first time.
In it you'll find a more detailed account of the most important things you need to know about sleep, alertness, dreams, and sleep disorders. Studies, statistics, plus plenty of Dr. Dement's classic anecdotes painting the history of sleep medicine.
A revolution in personal sleep tracking, the Zeo is a wireless headband that transmits your brainwaves in realtime to a dock (pictured here) or your smartphone. The result? You can wake up and see exactly what stages of sleep you were in during the night! Unprecedented personalized sleep knowledge.
Ever woken up paralyzed? A surprising number of us have, believe it or not. But few know the actual causes of this phenomenon, and fewer still how to exert control over it. Dream researcher and sleep paralysis expert Ryan Hurd shares breakthrough insights into how to do just that.
The information found on this page and throughout this site is intended for general information purposes only. While it may prove useful and empowering, it is NOT intended as a substitute for the expertise and judgments of healthcare practitioners.
For more info, see our