What happens to your body during a nap?

Mostly the same things that happen when you sleep at night, just in a single cycle (usually) and over a shorter period of time. First you doze in that hinterland between wakefulness and sleep, which usually lasts around five minutes. Then, as you lose consciousness, you enter stage 2 sleep where your breathing slows, your muscles relax and your core body temperature falls. Brain activity slows down, too.

“Stage 2 sleep is really great for alertness and that pushing-the-reset-button kind of power nap,” says Prof Sara Mednick, a sleep researcher at the University of California, Irvine.

Some 10 to 25 minutes later, deep sleep (stage 3) begins, characterised by a particular type of brain activity called delta waves. Researchers believe this stage of sleep, which can last up to 40 minutes, is vital recovery time for the body: a biological restoration during which your immune system and other bodily systems get a kind of MOT, and your memories are consolidated.

Lastly there is stage 4 or REM sleep. At this point, you’re 60 to 90 minutes into your siesta. This is the point when dreams will be most vivid and your body will enter a sort of paralysis with muscles freezing up. The exception is your eyes, which move quickly beneath the eyelids.

“Rapid eye movement (or REM) sleep is good for creativity and perceptual processing and also semantic associations,” says Mednick, author of The Power Of The Downstate. “You learn new information and encode it and memorise it in slow-wave sleep, but you then integrate that new information into your semantic network during REM.”

Read more about sleep:

• What causes sleep paralysis?
• Do insects sleep?
• Does warm milk help you sleep?

Can napping make up for lost sleep?

The reason most of us want to grab a nap is not to hack our creativity so we can write a symphony before 5pm. Mostly, we’re just exhausted. Does a nap genuinely let you ‘catch up’ on sleep lost to late nights, insomnia or teething babies? Absolutely, says neuroscientist Dr Brice Faraut, author of Saved By The Siesta.

“The power of the siesta lies precisely in its capacity to produce certain effects of a night-time sleep, but in record time,” he says.

Sleep is sleep, is the point. It doesn’t really matter if you only grab five hours at night, if you make up for it with another two after lunch. You’re still putting the time in. One full sleep cycle lasts around 90 minutes, during which time your body passes through every stage of sleep and all the effects that come with them.

If you wake up from stage 2 sleep, you will likely feel more alert and less fatigued but, says neurologist Prof Guy Leschziner, it’s the deeper sleep cycles that are truly restorative on a physiological level.

“We think it’s the deep sleep, the slow-wave sleep, that is the most important in terms of restoration of function and its impact on blood pressure and various other things,” says Leschziner, author of The Nocturnal Brain.

“So in deep sleep, channels in the brain called the glymphatic system open up and there is an increased removal of metabolites or chemicals from the brain that have been built up during waking hours.”

One thing: don’t nap for too long or too late in the day because it will likely impact your night-time sleep. It might satisfy your homeostatic drive, which is your body’s internal need or pressure for sleep, but “if you take a long nap in the late afternoon, it’s highly likely that you’ll have a harder time getting sleep at night.”

Can napping make you more creative?

If you believe the likes of Thomas Edison, Albert Einstein and Salvador Dali, naps absolutely make you more creative. Many famous scientists and artists have relied on naps to sharpen their minds, solve problems or generate ideas. And modern research validates them, with papers showing improvements in a range of cognitive skills from creativity to motor learning after a nap.

Inspired by Edison’s method of micronapping described at the beginning of the article, Dr Delphine Oudiette of the Paris Brain Institute devised a study to test it. She presented study participants with a mathematical problem and, if they couldn’t solve it, they were asked to recline on a chair and rest.

After the break, those people who drifted into stage 1 sleep – that hazy, half-awake state before the shutters come down – were three times more likely to solve the problem than people who didn’t nap. “It seems we have a creative switch there when you doze,” Oudiette says.

Other areas of cognition seem better served by other phases of sleep. Attention and alertness come from stage 2 sleep.

“And we need slow-wave sleep [stage 3] to improve memory,” says Oudiette. “You need at least 40 minutes to get a good amount of slow-wave sleep – but that also increases the chance of sleep inertia and feeling groggy.”

She says there’s also evidence to suggest that naps can help with emotional response (something that toddlers’ parents may verify). “Short sleep may help us digest and regulate our emotions. So if you get an angry email, it might be a good idea to take a nap before you respond.”

Is there an evolutionary explanation for naps?

“All of our rhythms, sleep included, are due to evolution, due to living on a planet that has a Sun and a Moon. And all animals and plants and bacteria have these cycles of rest and activity,” says Mednick. Some of the processes that underpin our need for sleep, such as circadian rhythms and homeostatic drive, are thought to have evolutionary roots.

“All animals outside of humans are nappers,” Mednick adds. “It’s almost like, you know, the nappers are the ones that are more naturalistic and the non-nappers somehow have evolved out of napping.”

Culture plays a part, too. Siestas are an ingrained part of the Mediterranean lifestyle. In China, it’s normal for people to take naps in high school or during the working day. When Mednick studied the napping habits of secondary-age pupils in China, she found that those who don’t nap were more likely to have lower academic performance and misconduct. “It’s an interesting thought that where napping is a culturally embedded practice, nappers do better.”

How can a nap improve your health?

It’s hard to overstate the importance of sleep for healthy functioning of your body and mind. “The consequences of non-optimal sleep reverberate over time,” says Faraut.

“On a short timescale of a few days, it decreases several aspects of cognition, reducing attention, memory formation and the ability to generate ideas. If sleep quality remains poor for an extended period of time, the consequences spread further beyond cognitive functions into the realm of physiology, such as metabolism, neuroendocrine stress, immune and inflammatory systems.”

Research has often linked poor sleep to a higher risk of heart disease, obesity and other conditions. It also increases the dangers of co-morbidities like high blood pressure or diabetes, with a number of meta studies showing a link between poor sleep and the risk of an early death.

If naps improve your overall sleep, they have the potential to counteract all of the above. “Studies conducted all over the world show that napping is an adjustable, all-purpose remedy for sleep deficit, a ‘medicine’ for the future, many of whose virtues are now known to us,” says Brice.

“A nap provides all the benefits to be had from the physiological functions of a night’s sleep, only on a smaller scale. There is growing scientific evidence that napping not only boosts alertness and cognitive performance, but also reduces the activity of the stress systems and normalises the immune dysfunctions reported as a risk of sleep debt.”

So the next time your boss asks why you fell asleep in the mid-afternoon meeting, remember: you’re not just resting your eyes; you’re giving your entire body a science-backed reset.

Why do some people feel worse after a nap?

Some people don’t wake up from a nap feeling restored, they feel drugged. They’re lethargic, they can’t focus and various cognitive abilities are impaired. The feeling is known as ‘sleep inertia’, describing the zombie-like state between sleep and wakefulness. If you wake from a nap feeling like that, it could be one of two things: bad timing or possibly bad genes.

For most people, waking up from deep sleep (stage 3) is harder. This may be something to do with the delta waves that characterise your brain activity at this stage, or it could be something to do with lower blood flow around your body.

One way to counteract this when you’re napping is to set an alarm that goes off not during stage 3, but stage 2: around 20 to 30 minutes after you drop off. This means less sleep, but more energy on waking.

It’s also possible that you’re just not a napper. “We tried to train non-nappers to gain benefits from a nap and found that over a month of nap training there was zero change,” says Mednick. “They didn’t gain any cognitive benefits and their sleep didn’t change. So there could be something fundamentally different between nappers and non-nappers.”

Mednick believes that just as people can have what’s known as different chronotypes – being a morning person or an evening person – it may be that we’re split into nappers and non-nappers. “It seems that there is something biological going on, but we need more research on that.”

Can too much napping be a problem?

Potentially. It’s not fully understood, but it seems you can have too much of a good thing. For all the benefits of some strategic shuteye, there are also a number of studies that have shown a link between naps and poor health, especially in older adults.

In 2020, a study presented at the European Society of Cardiology examined data from 20 papers. It found that people who often napped for more than an hour had a 30 per cent higher risk of (all-cause) death and a 34 per cent higher risk of cardiovascular disease compared to non-nappers.

One theory is that longer naps lead to inflammation in the body, which can increase the risk of heart disease over time. However, the same research suggested a protective effect from naps that could last for 30 to 45 minutes.

Meanwhile, researchers at the University of California, San Francisco, have linked excessive napping with neurodegeneration in older adults.

They found that those who napped for more than an hour a day had a 40 per cent increased risk of developing Alzheimer’s disease. But cause and effect isn’t clear here, says lead author Dr Yue Leng.

“It’s a vicious circle,” says Leng. “If you have an increased risk of dementia, you need more naps. And, if you take more naps in this age group, the risk of dementia increases.”

• This article first appeared in issue 381 of BBC Science Focus – find out how to subscribe here

What’s the best way to take a nap?

Like any kind of sleep, we’ll all have things that work and things that don’t when it comes to napping. Here are some soporific tips from our experts

Time it right

“The best times to nap are during the morning, between 9am and noon, to recoup some of the REM sleep lost by interrupting your night sleep too early,” says neuroscientist Dr Brice Faraut. “The other time to try is during the early afternoon – for a siesta.”

Make it a habit

“Humans are driven by consistencies,” says sleep researcher Prof Sara Mednick. “If you want to try establishing naps as part of your routine, try to find a time that you can consistently devote to napping. Make that the time when you just shut off.”

Lie back

“The ideal napping position is lying flat on a bed or sofa,” says Faraut. “If these aren’t available, sleep seated in an armchair and tilt the backrest by at least 40°. Use a neck cushion to support your neck.” He also says it’s best to banish blue light from screens.

Have a coffee first

It sounds counterintuitive, but if you want a restorative nap and to wake up feeling alert, you can try a coffee, says neuroscientist Dr Delphine Oudiette. “The caffeine will take maybe 40 minutes to kick in, so you can boost the effect of waking up feeling alert.”

Make sure you wake up

For a brief power-boost, hold an object in your hand when you nap. “When it falls, you should feel better rested with great ideas,” says Oudiette. “Put an alarm on for 20 minutes for a longer nap. And wake up rested, without the sleep inertia effects.

---