I have been an afternoon napper for more than 14 years. I started napping after moving to a country where most people took a siesta. For various reasons, I just couldn’t get enough sleep during the night, so it was easy to fall asleep.
Over the years, I have tried short power naps, 60-minute naps, and occasionally 90-minute mid-afternoon sleeps. In this post, I would like to share with you how to nap for better mood, alertness, concentration, improved memory, and restoration of learning capacity. We will cover how long and when to nap for maximum benefit, how to avoid after-nap grogginess (sleep inertia), and the possible risks associated with longer naps.
As a final point, I am going to share my personal napping experience and my favorite napping hacks.
The benefits of napping are numerous
For me personally, the most important benefits are improved mood and decreased sleepiness. I just feel happier and ready to tackle my afternoon after a nap.
Napping studies have found a large number and variety of benefits of napping in all kinds of workplace and operational settings. Studies looked at drivers, commercial airliner pilots, shift workers, doctors and nurses, students, children, senior citizens…
Here is a non-exhaustive list of research-proven benefits:
- Improved cognitive performance
- Increased alertness and concentration
- Decreased reaction time
- Speed and accuracy improvement on cognitive tasks
- Better mood
- Less sleepiness and fatigue
- Significantly reduced number of driving incidents such as drifting out of one’s lane in a car simulator experiment: the number of incidents caused by drivers who had taken a 15-minute coffee nap (see below for details) was 91% less than for drivers who had just taken a break. Coffee alone reduced the number of incidents by 66%.
- In a NASA study, pilots who took naps were able to maintain their performance and reduce incidents during a demanding multi-day schedule. Pilots who weren’t allowed to nap experienced deceasing performance and a significantly larger number of incidents, including during the descent and landing.
- Significantly Improved memory and protection of learned information from interference: a study that focused on declarative learning found a 60% increased memory retention for nappers at a final test one week after initial learning, compared to learners who hadn’t napped.
- Nappers perform better at abstracting general concepts and making connections that weren’t directly learned but can be inferred from what was learned (relational memory).
- A nap can restore the capacity to learn, which otherwise deteriorates considerably with time awake.
- Performance on a creative problem solving task where subjects had to find a linking word between three seemingly unrelated words was improved by more than 40% after a 90-minute nap containing REM sleep (see below) compared to rest and naps containing only non-REM sleep.
To better understand what nap length you should aim for, here is a sleep architecture primer
During sleep, we repeatedly cycle through 5 different sleep stages. They can be distinguished by the types of brainwaves (frequency and amplitude) that are dominant in each stage. A complete cycle lasts for about 90 minutes with individual variations. Assuming you get 7.5 hours of night-time sleep, you complete 5 sleep cycles.
Stages 1 and 2: Light sleep. It is easy to wake up from these stages.
Stages 3 and 4: Slow wave sleep (SWS). These are the deepest sleep stages, with slow heart rate and breathing. People who get woken up from slow wave sleep tend to feel confused and groggy. This grogginess can last for a considerable time and is also called sleep inertia.
Rapid Eye Movement Sleep (REM sleep): During REM sleep, the brain is very active and vivid dreaming occurs. This stage can be identified by bursts of rapid eye movement that occur throughout. Most of our remembered dreams occur during REM sleep. Waking up from REM sleep is not as hard as from SWS, but can still lead to some sleep inertia.1
The following diagram illustrates how a sleeper repeatedly cycles through the different sleep stages:
While the length of each cycle is about the same, the distribution of the 90 minutes to the different stages changes throughout the night. We get most of our slow wave sleep (stages 3 and 4) during the first half of the night and most of our REM sleep during the second half. Stage-2 sleep is roughly evenly distributed.
How long should you nap
- If you are looking for a refreshing power nap, set your alarm to between 15 and 20 minutes.
- If you are napping for learning and memory improvement, you need to sleep for between 60 and 90 minutes. (for more on memory naps, see below; also check the section on the downside of napping.)
The optimal nap length for a power nap
To reduce sleepiness and improve mood, alertness, and general cognitive performance, aim for 15 to 20 minutes total time in bed to begin with. Assuming you need 5 minutes to fall asleep, this will lead to between 10 and 15 minutes of sleep, and minimal, if any, slow wave sleep (SWS).2 Remember, you don’t want to be woken up during SWS.
In several studies, a nap of 15 to 20 minutes (this includes time to fall asleep) has led to significant improvements in alertness and performance, and no sleep inertia; that is, the improvements were almost immediate after waking up from the nap and lasted for several hours. To me, this is the perfect power nap.
You might ask, why not 5 minutes and why not 30?
You want to achieve better performance, i.e., better perception, attention, concentration, and reaction time after the nap. For this, 5 minutes are not quite enough. On the other hand, if you set the alarm to 30 minutes, assuming that you need 4 minutes to fall asleep, you sleep for 26 minutes straight. If you are unlucky, this might lead to a 30-minute bout of sleep inertia; that is, grogginess and decreased alertness after the nap.
Not all factors contributing to sleep inertia are currently known. However, waking up from SWS has been associated with reduced alertness and performance immediately after the nap. Generally, the more you are sleep-deprived and the later you take your nap, the faster you can expect SWS to set in.
In one study comparing naps of different duration, participants were allowed about 5 hours of sleep on the night preceding the experiment, so they were slightly sleep deprived: a 10-minute nap, preceded by 4 minutes to fall asleep (sleep onset latency), led to immediate significant alertness and performance gains after napping, lasting for 2.5 hours. The nap contained less than 1 minute of SWS.
Participants in the 20-minute nap group, however, (again +4 minutes sleep onset latency) only benefited from increased alertness and performance after a 35-minute delay.
The third group, which slept for 30 minutes, clearly suffered from sleep inertia after awakening (Brooks & Lack, 2006, see table below).3
Here is a small selection of the power nap studies that have shown the benefits of short naps.
If you want to mimic them, set the alarm to the total sleep time plus sleep onset latency.
When is the best time to take a nap?
Schedule your nap during the afternoon dip most people experience between 1 and 3 pm. During your personal dip, sleep propensity is high, and you might only need one or two minutes to fall asleep. Naps that are taken during this period have been shown to be more effective than in the morning or evening.4
The start time for power naps in many research studies finding positive effects was between 2 and 3 pm. But, short naps at 12:30 after a 30-minute lunch break were also effective.
In some experiments, naps at 2 pm have been more effective than at noon. I usually schedule my nap between 1:30 pm and 2:00 pm as this still gives me enough time to enjoy a post-nap afternoon coffee without interfering with my normal sleep. I have to drink my coffee before 4 pm to be on the safe side.
Experiment, go for a walk before you nap
These days, I usually don’t nap directly after lunch, but try to move first. After each meal, blood sugar levels rise even in healthy people. Blood sugar spikes, whether due to disease or excessive sugar intake, are not healthy and can be followed by subsequent low blood sugar levels, accompanied by a feeling of sleepiness. A 15-minute walk thirty minutes after a meal can help to blunt these spikes.5
I know, not everyone has the time to do both; for many years, I didn’t, but maybe you do. Maybe after walking, you find that you don’t even need a nap.
The downside of napping
A number of observational studies, most of them focusing on older people, have found an association between napping and the risk for cardiovascular disease, diabetes, and all-cause mortality, while a smaller number of studies have found no such association. Some studies have reported a reduced risk for heart disease in habitual nappers.
Short naps differed from long naps
Recently, a group of Japanese researchers led by Dr. Yamada at the University of Tokyo conducted a meta-analysis of these observational studies, covering a total of about 300000 people from different countries, including China, Germany, Greece, Israel, Japan, the UK, and the U.S., to investigate a possible association between habitual napping and the risk for metabolic diseases.
They reported that long naps ≥ 60 minutes were associated with an increased risk of diabetes. There was no association for naps of up to 40 minutes, followed by a sharp increase in risk for longer naps.6
In a second paper, Dr. Yamada and colleagues reported that long naps ≥ 60 minutes were associated with cardiovascular disease and all-cause mortality.
Again, short naps did not show an association with either one; cardiovascular disease risk decreased slightly for naps of up to about 30 min, then increased slightly for naps of up to 45 minutes, and then increased sharply.7
The authors acknowledged that their study doesn’t show that longer naps actually cause heart disease.
The fact that two events occur together doesn’t mean that one causes the other. People with hidden heart disease or diabetes (or other confounding illnesses) might feel more tired and inclined to take long naps. Daytime sleepiness and night sleep disorders have also been associated with a higher risk for diseases.
Nevertheless, I take this as to not make my regular naps longer than 30 minutes.
Usually, I aim for 15-to-20-minute power naps. I do use longer naps occasionally as a tactical tool though, because they have unique benefits for learning and memory as described below.
Napping can also improve memory and prevent learning burnout
One type of memory that is very important for students and life-long learners alike, and has been extensively researched in sleep studies, is declarative memory. Declarative memory refers to two types of memory: episodic memory and semantic memory.
Episodic memory is memory for events: You remember a piece of information together with the time and place (and possibly other specifics) where you learned this information. For example, this could be when and where you had your first kiss.
Semantic memory is memory for facts and general knowledge independent from a particular learning episode. You likely know that Washington, D.C. is the Capital of the U.S., but you may not know when you first learned this information.
Several sleep studies have found that napping helps to improve declarative memory, in particular associative memory; that is, napping helps to strengthen newly learned associations between pieces of information and protects them from interference. This is important for reading comprehension, learning a new language, and studying in general. For example, to learn German foreign language vocabulary, you have to associate a word’s meaning, say apple, with its German pronunciation and spelling – “Apfel.”
Sleep to strengthen and consolidate your memories
New memories get encoded through making and strengthening connections in different brain regions. Initially, these connections rely heavily on a brain structure called the hippocampus. The hippocampus acts as a temporary store for associative memories while the connections in the neocortex (the part of the brain in which they are “permanently stored”) are not yet strong enough.
With time, these memories get consolidated; that is, they become increasingly independent of the hippocampus: During sleep, in particular during SWS, memory traces in the hippocampus and neocortex get reactivated. This reorganizes and strengthens these memories in the neocortex and over time leads to long-term, hippocampus-independent memories.8 They also become more resistant to interference from later learned information.
Sleep to connect the dots
Likely as a consequence of this consolidation, relational memory and the ability to abstract general concepts from the learned information are also improved after a nap.9,10 Relational memory refers to associations that weren’t explicitly learned, but could be inferred from previously learned information.
A nap can restore your learning capacity
Have you ever had the feeling “I am full, I can’t possibly take in any more information” at some point during the day?
Our capacity to learn new information declines with time awake.
The good news: it can be restored through napping. In a study conducted at the University of California, Berkeley, learning capacity was completely restored at 6 pm after a 100-minute nap (2pm – 3:40 pm) compared to baseline (12 pm).11
Participants who weren’t allowed to nap exhibited a significantly reduced learning ability at 6 pm.
It is assumed that so-called synaptic downscaling during sleep prevents this learning burnout: it prepares the brain to make way for new information to be learned after sleeping.
You need to nap for 60 to 90 minutes for learning and memory improvement
Several newer studies are indicating that to improve your memory for what you have learned, protect these memories from interference, and make way for learning new information, you need to nap for about 60 to 90 minutes.12
Here is the sleep data from three nap studies focusing on learning and declarative memory
The first two focused on memory retention, while the third one showed that naps can restore learning capacity.
Short naps, including a 10-minute nap with stage-2 but without SWS sleep, have also been shown to have a positive effect on memory. However, in a recent associative memory nap study, these effects were short-lived and only present during a first test starting 75 minutes after learning. During a second test following an interference task (a second learning task), there was no difference between participants who had stayed awake and participants who had napped for 10 minutes.
However, a 60-minute nap, containing a significant amount of SWS, protected against interference and led to superior memory retention even during a final test one week later: 60-minute nappers remembered 60% more than participants who had stayed awake after learning or napped for 10 minutes. There was no difference between the 10-minute nap group and the stay-awake group.13
1. The coffee nap
In 1996 and 1997, English researchers Reyner and Horne looked at the efficacy of naps and caffeine to reduce sleepiness and driving impairment in sleep-restricted drivers (5 hours sleep due to delayed bedtime the night before).
They had participants drive for 30 minutes along a monotonous highway in a car simulator, followed by a 30-minute break and then another 120-minute drive. Drivers had to stay within their lane and avoid collision with a suddenly appearing slow vehicle (once per hour).
Five minutes into the break, drivers either had a nap (earlier experiment from 1996), coffee with 150 mg caffeine followed by a 15-minute nap (terminated 5 min before the second driving period), coffee with 200 mg caffeine, or as control condition, decaffeinated coffee.
Coffee-nap drivers performed significantly better than coffee-only drivers, who in turn had significantly fewer incidents than placebo drivers. Comparing the data with their own earlier experiment from 1996, the authors concluded that the coffee-nap drivers also performed better than drivers who had only had a nap.14 The coffee nap works because caffeine needs 15-30 minutes to kick in.
How to do the coffee nap: Just drink a strong cup of coffee (5 grams of regular instant coffee powder contain about 160 mg caffeine) or take a caffeine tablet. Then take a nap for about 15 minutes. You might still want to set the alarm to 15 to 20 minutes because there is no guarantee that you will wake up after 15 minutes. After a night with too little sleep, I can easily nap for 45 minutes after drinking a strong cup of coffee.
To learn more about how I use coffee and other hacks to improve concentration and alertness, also read this post.
2. How to wake up after a nap and avoid sleep inertia:
Power nap: Set your alarm to 20 minutes. This allows for 5 to 10 minutes of sleep onset latency and an effective power nap that improves mood, alertness, and cognitive performance.
Self awakening: Many people are able to instruct themselves to wake up at a specific time. This allows for a smoother transition compared to been woken up by an alarm clock. In an experiment, older people were either told to self-awaken after 20 minutes or woken up: in the self-awakening group, blood pressure rose more gradually and heart rate did not show a rapid increase (it did in participants who were woken up).15
Try this: Tell yourself you are going to wake up in 20 minutes, and see if it works for you. As a precaution, you can set an alarm timer to 30 – 35 minutes.
Remind yourself via a fading background sound: Some white noise apps (see hack 5) come with a fade-out function. You preset when the sound of a water stream or fan should stop, and the app slowly fades out the sound at the preset time. This may be less startling than an alarm and, together with your intention to wake up, all you need to return from your nap. You could also create this effect by slowly fading out a sound file with your desired nap length.
Learning and memory improvement nap: If you are looking to nap for learning and memory improvement, you need to experiment. While 60 minutes have been effective for memory improvement, they might leave you groggy for some time after waking up. During most nap studies focusing on learning and memory, they had people hooked up to an EEG and only woke them during a lighter sleep stage. That’s not yet an option for home use. Provided you have enough time, nap for 90 minutes to finish a complete sleep cycle. If this leaves you groggy, add another 5 minutes… If you wake up naturally without feeling crappy, that’s even better.
3. Use scents during learning and napping
Re-exposing a sleeper during short wave sleep to the same scent that was present during learning has been shown to enhance memory for the learned information.16,17 Try perfume, fragrance oil, or an electric fragrance lamp while learning, and use it again during your nap. Just make sure that the scent isn’t bothering you and that your setup is safe.
4. Test yourself on what you have learned before you nap
As a reader of my Blog, you probably know that I am a fan of reciting information and self-testing. The efficacy of recall practice for memory improvement has been shown again and again. Researchers in a nap study compared two learning conditions: One with, one without a test for the learned material. Their data showed that to get a memory boost from napping, you need to have learned the material well. Only participants who had been tested on the material benefited from the following 60-minute nap.18
So before taking a nap, mentally go through what you have learned (without re-reading the material) and probe your memory on the important questions. Then take your nap.
5. Use a white noise app for your smartphone or your iPad to guide you into sleep:
These apps let you choose between different natural soundscapes, such as ocean waves, water streams, the humming of a fan, or pure white noise (that’s what you hear when an analog radio or TV is not tuned into a station). I use the white noise app by Tmsoft, which is available for all major platforms, including Android and iOS. Depending on your preference, listen to the sounds through speakers or earbuds. To wake you up on time, preset your phone’s countdown timer, or have the app fade out the sound at a preset time for a smoother return to the material world.
6. Put on earmuffs to cut out the noise and cover your eyes with a sleep mask:
If you work in an open office environment or in a lab on campus, you may not be able to get a perfectly quite environment for your nap. Industrial earmuffs significantly attenuate ambient noise levels. Combine them with earbuds to listen to your white noise app and wake you up on time. Alternatively, invest in good noise-cancelling headphones.
How do I nap?
As mentioned earlier, I usually start my nap between 1:30 and 2 pm. I nap while lying on my back, with one pillow supporting my back and one supporting my legs. (During the night, I usually sleep on the side.) I set my iPad’s countdown timer to 23 minutes, put in earbuds, and listen to a water stream using a white noise app. To block out light, I cover my eyes with a sleep mask. My mind tuning into the sound of flowing water, I need between 5 and 10 minutes to drift away. This gives me a power nap of between 13 and 18 minutes, and if I am not too sleep deprived, the alarm brings me back refreshed and ready to brew an afternoon coffee.
I am quite sensitive to noise; sudden bass-heavy noise in particular startles me and cuts my nap short, so when I am in a noisier environment, I wear noise-isolating ear muffs on top of my earbuds. Good noise-cancelling headphones do pretty much the same. They are definitely more comfortable, but also quite a bit more expensive.
In the past, I have also successfully napped without any sound, and with binaural beats created for napping. Water streams, calm ocean waves, and binaural beats all work well for me.
My nap is a refuge from the bustle and almost always lifts the curtain of fatigue. In the past, when I didn’t get enough sleep, my days sometimes felt like a real drag. Naps are a great antidote and give me something like a second morning awakening.
What is your experience with napping? What are your favorite napping hacks? I would love to hear about them in the comments section below.
- See Napping Notes for references.
- Image credits:
- Sleep Hypnogram between Midnight and 6.30 am, modified Sleep_Hypnogram.svg, by RazorM, used under CC-BY-SA-3.0-MIGRATED
- Reading activates your imagination, Danzajicek via Openclipart.org
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