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The Importance of Sleep

The past few years have seen increasing information in the media on the importance of sleep for health and wellbeing. It is an area that comes up in my coaching conversations on a regular basis. While I had an intuitive understanding of the value of good sleep, I had limited knowledge of the mechanics of sleep or the science and evidence that supports its influence on many key human functions. I’ve recently read Why We Sleep by Matthew Walker (Walker, 2017), which is easy to read and provides a wealth of information on the science of sleep. In this article, I am pleased to share my key learnings from this book, along with the accompanying infographic.

Circadian rhythms

We each have our own circadian rhythm, the 24-hour clock cycle that controls when you are awake and when it’s time to sleep. There are three different rhythms, or chronotypes, that we fall into.

· 40% are morning types (morning larks)

· 30% of people are evening types (night owls)

· 30% are in between with a slight leaning towards evening

These different rhythms and staggered sleeping times may be an evolutional adaptation to protect a sleeping group from predators by limiting the period that all members were asleep.

Circadian rhythms are genetically inherited, and are controlled by the suprachiasmatic nucleus in the brain. The circadian rhythm activates numerous brain and body functions, including those that keep you awake and alert during daylight hours. These processes are reduced at night with a resulting lowering of alertness. Body temperature follows this rhythm, increasing during the day, peaking late afternoon, then gradually lowering towards bedtime, reaching its lowest point approximately two hours after sleep. This lower body temperature at night is one of the reasons why we sleep less well when it is hot, and it is recommended to lower your night-time bedroom temperature to improve sleep quality.

Many work and school schedules unfairly discriminate against night owls, who may be physically awake, but whose brains remain in a sleep-like condition during the early morning. The brain’s prefrontal cortex, which controls logical reasoning and high-level thinking, is not fully switched on for night owls in the early morning. Night owls should schedule important events and tasks later in the day when possible. Conversely, morning larks should try to avoid the later afternoon and early evening when their alertness and attention are waning. I suggest that the case for flexible working arrangements that enable each individual to perform during their peak times is supported by the evidence of these varying chronotypes.

Biology of sleep

There are a number of hormones and chemicals that are at work to control being awake and sleeping.


The circadian rhythm is powered by melatonin. This hormone increases in the bloodstream as daylight fades and is the signal for sleep to start. The concentration of melatonin decreases during the night and is no longer released as light enters the brain in the morning.


The second key chemical is adenosine, which functions independently from the circadian rhythm, although the two are usually in sync. Adenosine increases in concentration throughout the day, and creates sleep pressure, the feeling of sleepiness. Adenosine functions to dial up the areas of the brain that induce sleep and dial down those the promote being awake, and is cleared from the brain through the process of sleep. Stimulants, such as caffeine latch onto the adenosine receptors and mask the signal to sleep. Because the half-life of caffeine is 5 to 7 hours, it is recommended to limit consuming caffeine in sufficient time for your body to have flushed it from your system, thus allowing adenosine to do its job of inducing sleep. Decaffeinated coffee contains between 15% to 30% of the caffeine of a regular cup of coffee. Beware of decaffeinated drinks later in the day, especially if you are more susceptible to the stimulating effects of caffeine.

Afternoon naps

There is a biologically programmed mid-afternoon drop in alertness. It’s advised not to schedule important events at this time (the post-lunch conference slot or interview, for example!) Many cultures have a mid-afternoon nap (biphasic sleep pattern), but work hours in numerous countries don’t encourage a post-lunch snooze, forcing workers to follow a monophasic sleep pattern, against our biological makeup.

Mechanics of sleep

There are two primary sleep stages: non-rapid eye movement (NREM) or deep sleep, and rapid eye movement (REM), which we know as dream sleep, although dreaming can occur in other stages. NREM is further divided into Stage 1, Stage 2 and Stages 3 & 4. The deepest sleep, from which it is the most difficult to wake an individual from, is Stages 3 & 4. NREM and REM sleep are equally important and each play a different role.

NREM sleep

During NREM sleep, memories are moved from the hippocampus to the cortex, transferring information from its temporary storage place in the brain to long-term storage. This particularly occurs during Stage 2 of NREM sleep (with electrical activity in the brain called sleep spindles), and this process then frees up space in the short-term storage area to allow new memories to be saved. NREM sleep therefore has the greatest impact on fact-based learning, with quality sleep both before AND after learning important for retention of information.

Stage 2 NREM sleep is also critical for the enhancement of motor skills, most particularly during the last 2 hours of an 8-hour sleep cycle.

NREM sleep also has the function of cleansing the brain of harmful contaminants. There is a balancing effect of sleep between the amygdala and the pre-frontal cortex, which respectively control emotions and decision-making. Lack of sleep results in the pre-frontal cortex losing control of the striatum, with associated emotional swings from positive to negative. The fight-flight area of the brain also becomes overactive when sleep-deprived.

REM sleep

Brain scans of individuals in REM sleep show an increased activity in many parts of the brain. These include areas that help with complex visual perception and movement, those associated with autobiographical memory and the areas that help to produce and process emotions. Some areas of the brain are deactivated during REM sleep, such as those that manage logical and rational thought and decision-making. This helps to explain the unhelpful swirling thoughts that can plague us at night, when our brain is dialling up its emotional centre but dialling down the logical centre.

The purpose of dreams

Walker describes the emerging research and evidence of the purpose of dreams, which is suggested to be two-fold: supporting emotional and mental health and in problem-solving and creativity.

Emotional and mental health

Chemical changes occur in the brain during REM sleep. Noradrenaline, a stress-related chemical, is closed off. One outcome of REM sleep is to reduce the negative emotions that are associated with painful events. Walker describes his research with patients with post-traumatic stress disorder (PTSD), whose high levels of noradrenaline prevented these individuals from entering REM sleep. This stopped them from being able to deal with the emotions attached to the trauma.

REM sleep also recalibrates the ability to read the facial expressions and interpret the emotions of others, which would have been a critical survival skill, and remains important in work and social situations and relationships.


Experiments have demonstrated the value of REM sleep in problem-solving, with participants showing 15-35% increased ability to solve puzzles when woken from REM sleep than from NREM sleep. There was also, surprisingly, a similar level of enhanced performance related to REM sleep when compared to the ability to solve the puzzles during the day. Another experiment describes how, in REM sleep, the brain may skip links and logical hierarchies, reducing linear thinking, thus allowing for greater creativity. While NREM sleep aids in learning, REM sleep facilitates comprehension and the ability to connect seemingly disparate facts to weave complex solutions.

Sleep cycle

An average eight-hour sleep cycle comprises around five approximately 90-minute cycles with varying lengths of NREM and REM sleep throughout the night. The earlier cycles have a higher amount of NREM sleep while the later cycles shift more towards REM sleep. There is also a shift in the type of NREM sleep, from Stages 3 & 4, the deepest sleep, earlier in the night, to Stage 2 towards morning. Going to sleep later can disrupt the critical functions that NREM sleep provides, while getting up early will have an adverse impact on REM sleep.

Amount of sleep needed

The amount of sleep needed varies throughout life. Babies need the most at 16-18 hours per night, school-age children and teenagers need around 9.5 hours, while adults need 7-9 hours (National Institute of Neurological Disorders and Stroke, 2022).


Along with many other aging issues, sleep is impacted as we grow older. The electrical quality of sleep has been reduced by our 40s, and by late 40s, 60-70% of deep sleep has been lost. This increases to 80-90% loss in our 70s.

Sleep is more fragmented as we age, with the efficiency of sleep (amount of time asleep during a sleep cycle) dropping from 95% as teenagers to 70-80% efficiency aged 80. Good quality sleep is suggested at 90%.

Our circadian rhythms also change as we age, with melatonin released earlier resulting in the need for earlier bed times.

Jet lag

It takes a day to recover from a one-hour change in time due to travel across time zones or the transition to and from daylight saving time. Some sobering research shared by Walker describes how the rate of heart attacks increases significantly the day after daylight saving time starts in spring, and that the opposite effect is seen when there is an extra hour of potential sleep time in autumn. Traffic accidents also show a similar trend. A missed hour of sleep can have serious outcomes!

Effects of sleep loss

A number of consequences of sleep loss are described by Walker. These include cancer, heart attacks, diabetes, weight gain and obesity, reduced testosterone levels in men and fertility in women, reduced immune system functioning, Alzheimer’s and a shorter life span. There is also increasing evidence for the link between psychiatric illnesses and sleep disruption, with bipolar disorder mentioned as one of the areas studied. Conversely, research has demonstrated that improved sleep can help with a number of mental illnesses and conditions, such as depression and anxiety.

As mentioned, lack of sleep is also linked to an increased number of road accidents. The recycle rate of a human is approximately 16 hours. The brain starts to fail after being awake for this length of time. Adults need ‘more than seven hours of sleep each night to maintain cognitive performance’ (Walker, 2017: 140).

From a work perspective, there is a particularly interesting study detailed by Walker in which supervisors tracked the amount of sleep they had over several weeks and their leadership performance was evaluated by their employees. Poor self-control and increased abusiveness towards employees by supervisors was predicted by their lower quality of sleep. Further, employees, who may themselves have had good quality of sleep, were less engaged in their work after a supervisor reported poor sleep. Food for thought!

Getting a better night’s sleep

Walker offers a number of ways in which sleep can be improved, and includes top tips from the National Institutes of Health (NIH MedlinePlus, Summer 2015) as an appendix to the book. These are shared in the accompanying infographic. One recommendation that is particularly relevant in today’s switched-on world is to avoid the use of mobile devices at least two hours before bed, as the blue LED light impedes the increase in melatonin required to signal sleep.


In this article, I’ve shared some of the areas of Why We Sleep that particularly piqued my curiosity and helped me to understand the mechanisms and functions of sleep better. One topic that I’ve not covered is sleep in children, teenagers and young adults, which could be of great interest to parents and teachers. As you will have discovered from this short summary, ‘sleep is not the absence of wakefulness’ (Walker, 2017: 108) but a fundamental building block for health and wellbeing. Exploring your quality of sleep, as a part of a coaching programme, could support changes to benefit many facets of your work and life.


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