While there is still much that is unknown about sleep, its importance in daily life is well-established, especially as the body of research has grown over the past few decades.
According to a summary of current research published by the US’s National Institute of Neurological Disorders and Stroke (Ninds), “everyone needs sleep, but its biological purpose remains a mystery. Sleep affects almost every type of tissue and system in the body – from the brain, heart, and lungs to metabolism, immune function, mood, and disease resistance. Research shows that a chronic lack of sleep, or getting poor quality sleep, increases the risk of disorders including high blood pressure, cardiovascular disease, diabetes, depression, and obesity.”
Naps however, are an even lesser understood area of sleep. According to a 2017 study by researchers from the University of Massachusetts’ Neurosciences and Behaviour programme, titled Exploring the nap paradox: are mid-day sleep bouts a friend or foe?, “It is well established that in addition to reducing sleepiness, mid-day naps offer a variety of benefits: memory consolidation, preparation for subsequent learning, executive functioning enhancement, and a boost in emotional stability.”
The paper goes on to state that these benefits remain present even if a sufficient amount of sleep is obtained during the night prior, and that daytime naps do not necessarily affect the quality of nocturnal sleep.
Sleep: The breakdown
To understand how naps benefit us and how long they should be, it is important to understand the two established primary stages of sleep, which we cycle through several times during a typical night. As per the study mentioned above, as well as the summary of current research from the Ninds, the first stage of sleep is non-REM (non Rapid Eye Movement) sleep, which in itself is split into three stages. The first, which lasts a few minutes, is relatively light sleep, during which heartbeat, breathing, and eye movements slow, and muscles relax, with occasional twitches. The brain waves also begin to slow from their daytime wakefulness patterns.
This is followed by the second stage of non-REM sleep, where the heartbeat and breathing continue to slow down, and muscles relax even further. The body temperature drops; eye movements stop. You’ll spend more of your repeated sleep cycles at this stage than other sleep stages through the night.
Then the third stage of non-REM sleep is that deep sleep stage which we all need to feel refreshed in the morning. Here the heartbeat and breathing slow down to their lowest levels. The muscles are at peak relaxation and the brain waves are even slower. This stage is also known as slow wave sleep (SWS).
The other sleep stage is known as REM (rapid-eye-movement) sleep. Here, “The eyes move rapidly from side to side behind closed eyelids. Mixed frequency brain wave activity becomes closer to that seen in wakefulness. Your breathing becomes faster and irregular, and your heart rate and blood pressure increase to near waking levels. Most of your dreaming occurs during REM sleep. Your arm and leg muscles become temporarily paralyzed, which prevents you from acting out your dreams,” according to the Ninds. REM sleep typically comes at about 90 minutes after falling asleep, completing the initial sleep cycle.
Naps, on the other hand, have a different physiology than a full night’s sleep. As per the above-mentioned 2017 study, “Only recently has the physiology of naps in healthy individuals been considered. In infants, naps are indistinguishable from nocturnal sleep, as both are REM-rich. Later during early childhood, naps are predominantly composed of NREM sleep with very little REM. Young adult naps, if of substantial length, will contain both NREM and REM bouts. Naps of older adults are dominated by lighter NREM stages, a short bout of SWS, and less often, REM sleep.”
How often should I nap?
The length and frequency of a nap are not exactly standard, and neither are the lengths of naps that have been researched. A study by researchers from the University of California’s Department of Psychiatry, published in 2012 and titled The effect of nap frequency on daytime sleep architecture, takes a closer look at how the frequency of naps affects the quality of the naps.
The researchers studied 27 healthy non-smoking university students between the ages of 18 and 35, who all took a series of 75-minute naps. They found that, “The more individuals nap during a week, the greater the amount of Stage 1 [non-REM] and Stage 2 [non-REM] sleep and the less SWS [deep sleep] in their naps…. subjects in the 1-2 nap [per week] frequency bin had significantly more Stage 2 sleep than subjects who took 3-4 naps [per week] or subjects who took zero naps. Within NREM sleep, these data show a progression from deep sleep to lighter and lighter stages of sleep based on nap frequency – people who did not nap the week prior had the highest amount of SWS [deep sleep], people who took 1-2 naps had the most Stage 2, and people who napped the most (3-4 naps) had the most Stage 1 sleep.”
Keep in mind that SWS is the deep sleep stage where the muscles are fully relaxed, and where it might be more difficult to wake someone up. Waking up at this phase is also more likely to result in waking up feeling groggy and tired, negating some of the benefits of a nap. As per the study, non-nappers, or non-frequent nappers, “may be more inclined to avoid napping due to high levels of SWS that produce unpleasant after-effects”. However, according to the research, this is something that may improve the more frequently one naps.
Great! So how long should I nap?
In 2006, researchers from Australia’s Flinders University conducted research to measure the efficacy of different nap durations on subjects who had slept up to only five hours the previous night. The subjects were “twenty-four healthy, young adults who were good sleepers and not regular nappers”.
The researchers found that, “The 5-minute nap produced few benefits in comparison with the no-nap control. The 10-minute nap produced immediate improvements in all outcome measures (including sleep latency, subjective sleepiness, fatigue, vigor, and cognitive performance), with some of these benefits maintained for as long as 155 minutes. The 20-minute nap was associated with improvements emerging 35 minutes after napping and lasting up to 125 minutes after napping. The 30-minute nap produced a period of impaired alertness and performance immediately after napping, indicative of sleep inertia, followed by improvements lasting up to 155 minutes after the nap.” This led them to conclude that, “the 10-minute nap was overall the most effective afternoon nap duration of the nap lengths examined in this study”.
Research from subsequent studies, as published by the American Sleep Association, a group founded by physicians and scientists in 2002, found that for most people a good nap is between 15 to 30 minutes, with some doing better at 10 minutes, and others at 40 minutes. This way, nappers can avoid crossing over into deep sleep, and therefore not feel groggy when they wake.
Is that all? Can I go nap now?
As per the Ninds statement at the beginning of this article, “everyone needs sleep, but its biological purpose remains a mystery”. Hence, this is still very much an ongoing field of research. While research suggests that napping is great for children, and recommended for young as well as middle-aged adults, the current literature on its effects on older populations is inconsistent. The other study mentioned at the beginning of this article, the 2017 study titled “Exploring the nap paradox: are mid-day sleep bouts a friend or foe?”, was motivated in particular by other studies that associated napping “with a number of subsequent negative outcomes, including increased risk for hypertension, microvascular disease, depression, diabetes, osteoporosis, functional limitations, general medical morbidity, increased mortality, and cognitive decline. These associations have predominantly been identified in older adults but also exist in middle age and young adults.”
After aggregating findings from previous research, the authors of the study conclude by asking: “Should naps be prescribed?” And their answer is that indeed, “in healthy, young individuals, a mid-day nap is observably beneficial”. They go on to confirm the benefits mentioned above. However, when it comes to “older populations, as opposed to the obvious benefits of a mid-day nap outlined above, excessive napping has been linked with negative outcomes. Yet there is no direct evidence suggesting that mid-day napping is detrimental. Although it is unlikely that essential naps are causal in inducing comorbidities, it is perhaps premature to make this statement definitively. Therefore, it is also premature to prescribe napping in this population.”
They are not the only ones to highlight the inconsistencies; another study, published in 2016, titled Afternoon Napping and Cognition in Chinese Older Adults: Findings from the China Health and Retirement Longitudinal Study Baseline Assessment, also notes that “Long‐term cognitive function in older adults remains poorly understood, and the results in the literature are inconsistent. A few studies have reported that longer napping duration is associated with cognitive impairment, but other studies have found beneficial effects of napping on cognitive function.”
However, looking at subjects 65 years and older, their study concluded that “moderate nappers had better overall cognition than non-nappers or extended nappers. Non-nappers also had significantly poorer cognition than short nappers. In multiple regression analysis, moderate napping was significantly associated with better cognition than non‐, short, and extended napping.” DM/ML
"A fire broke out backstage in a theatre. The clown came out to warn the public; they thought it was a joke and applauded. He repeated it; the acclaim was even greater. I think that's just how the world will come to an end: to general applause from wits who believe It's a joke." ~ Søren Kierkegaard