This piece was written by one of our contributors; Psychology MSc student – Ellie Wright
We do it every day. It’s free, rarely has negative side effects, and is so important for our whole bodies: our mental and physical health (1, 2, 3). But we are becoming so bad at sleeping that experts and the Centre for Disease Control and Prevention have named the problem a sleep epidemic (4, 5).
Lifestyle behaviours can prevent sleep onset. Our 24/7 world encourages us to do things which disrupt our internal clocks. Examples include:
💡over exposure to light after dark (6)
🌕 too little daylight (7)
✈️transcontinental travel (8)
👩⚕️shift work (9)
🍿persistent snacking, including late at night (10, 11)
However, from the moment we open our eyes, we can make changes which protect sleep despite these demands.
Poor sleep (short or disturbed sleep) changes our bodies and behaviour (1). Understanding how can motivate us to prioritise habits which promote sleep onset.
The problem: how much do we sleep?
Not enough! Poor quality sleep is an increasingly common condition and normally presents as partial sleep deprivation day after day (12). How much sleep we need depends on our age. For adults, the recommendation is 7-9 hours (13, 14). Short sleep is growing trend around the world. In 1960 we were getting 8.5 hours sleep each night but now, on average, we are sleeping just under 7 hours, and around a fifth of us get less than 6 hours (15, 16).
Globally, we don’t prioritise sleep
We increasingly undervalue sleep. In Japan, where the average night of sleep is 6 hours, there is even a word for being present whilst asleep ‘inemuri’ (17). And, short sleep is learned from a young age: children’s sleep has declined by 70 minutes since the 1900s (15, 18).
What is sleep?
When we close our eyes, our brain’s activity changes. We cycle through five sleep stages, an average of four to five times a night with each loop taking progressively longer.
Each stage is characterised by electrical activity. Neurons in our brain start firing in synchrony like a Mexican wave, playing out a hormonal symphony (19). Our heart rate, breathing rate and brain activity gradually slow in stages one to four. Stage five: rapid eye movement sleep (REM) resembles wakefulness; our eyes dart behind our eyelids and the sleep stage cycle starts again (2).
How we fall asleep
We have sleep and wake promoting systems. These networks of neurotransmitters communicate brain state changes, working against each other to help and halt sleep (20)
Orexin is one of many important neuropeptides. This molecule signals the change in sleep/wake brain states, meaning we can only be in one at any given time (21). Without enough of it people seesaw between wakefulness and sleep; a condition we call narcolepsy (22).
Circadian rhythms: our 24 – 25 hour body clocks
Cells in our brains and bodies follow an internal master clock: our circadian rhythm. With each rotation of the sun around the earth, light intake and feeding behaviour resets our circadian rhythm to Earth’s 24 hour day. This is disagreement about the exact timing of our circadian clocks, but on average they are a bit longer than 24 hours, making daily reset vital (23, 24)
Each cell in our body has a clock (25). Light passes through our retina and into the circadian pacemaker – part of the brain called the suprachiasmatic nucleus or SCN. This brain region coordinates a complex hormonal circuit which sends signals to organs, muscles and tissues, synchronising our body with the time of day and helping promote sleep onset (21).
How well we sleep and eat in synchrony with night and day determines the healthy or disordered production of hormones which change our behaviour. These include hormones responsible for stress, appetite, sleepiness and insulin control (21).
Why we sleep
We spend a third of our lives asleep. Animal studies suggest without it we would die (27). But anything could happen while we sleep! Dr Alan Rechtschaffen summarises this problem: “if sleep doesn’t serve a vital function, it’s the greatest mistake evolution ever made” (28)
The variation of sleep habits in the animal kingdom suggest sleep balances benefits of rest with survival needs (29). Giraffes sleep for just two hours, perhaps because it takes 30 seconds to stand up, dolphin’s sleep with half a brain at time and bats sleep for 20 hours (30).
The benefits of sleep
Current evidence suggests sleep improves how we feel, behave and think and how much people like us (1, 31, 32, 33). It replenishes energy, “boosts” our immune systems, protects physical and mental health and prevents against psychiatric conditions (35 – 42). Poor sleep quality possess risks to mental and physical health. But how?
Sleep plays back memories to remember, emotionally process and strip them of emotional feeling without affecting content (31). Sleep studies show how dreams become progressively less negative throughout the night, preparing our mood for waking (32, 2).
Sleep helps us socially connect by improving our mood and opening our body language (1). People who did not know they were judging people involved in a sleep study, liked and trusted the control group who had normal sleep more than participants who had been partially sleep deprived on 4-5 hours for just one week (1).
🙁👭Sleep deprivation causes loneliness
This same study found that lack of sleep causes social isolation (1). It makes us hypersensitive so our body language changes and we sit further away. The fact that naive judges liked people who had just one week of partial like deprivation less than those who had slept 7-9 hours matters for our physical and mental health. Loneliness poses a risk to our physical health greater than tobacco or obesity (33).
Sleep helps sustain happiness. People tested on 7 hours sleep had good moods but when the same group of participants were sleep deprived, on just under five hours a night, their moods become low, halving on the happiness scale, and their emotional and physical complaints increased four fold (66). Their mental states returned to normal when they returned to sleeping seven hours a night.
🤔 Memory consolidation
Sleep helps us to remember and store and new memories (33). Avoiding disruption in the first half of sleep, when slow wave sleep dominates, facilitates this process (2).
🤓 Learning? Take a nap!
A nap helps consolidate learning, moving learnings from short-term memory in the hippocampus to long term memory in the neocortex. Brain scans show this relocation with lists of new words (34).
Our problem solving ability increases on difficult tasks after sleep. Rest activates the brain’s Default Mode Network which uses unconscious processing to find hidden rules (35, 36).
⏩ Maximising brain capacity
Forgetting is an important part of sleep. Our brains prioritise what we need to remember and forget what we don’t for sustainable and effective brain productivity (37).
Hormonal activity during sleep is vital for our physical health, particularly growth and repair. 60- 70% of growth hormones are released during first few hours of sleep timing. Without sleep, very little amounts are released (38).
Sleep acts as a power saving mode, reducing calorie use at a time when, if awake, darkness would make us inefficient (39). It helps us replenish brain energy stores; blood glucose consumption is twice as high when we are awake (40).
❤️ Sleep helps to protect against heart disease, cancer and stroke
Evidence suggests people who sleep 7-8 hours have lower rates of cardiovascular disease, cancer and stroke. Their immune systems have adequate sleep for healthy levels of growth and stress hormones, helping to maintain immunological memory which is key for fighting illness and disease (41, 42).
😒 Mood instability
REM sleep is really important for our psychological health. Just a week without enough of it, or if disturbed, can lead to memory problems and a lack of impulse control; we can become moody, irritable and aggressive (44).
🚗 😴 Decreased ability to pay attention and think clearly
Lack of sleep significantly reduces focus and our ability to process what’s happening around us (45). For drivers, this really matters. In experimental conditions, sleep restricted drivers, who didn’t feel tired, crossed motorway lines significantly more than well slept drivers (46). Sleep deprivation makes you 2.6 times more likely to fall asleep at the wheel (47).
👩⚕️ Decline in accuracy, speed and understanding
Shift work impacts workers more than we imagine. Despite care workers thinking they adapted to night shifts, when assessed for accuracy, speed and understanding their thinking performance was still just as impaired as the first night of their rotation (48).
🤕 Increased sensitivity to pain
If we don’t get enough slow wave sleep (stages 1-4), we are more likely to suffer from aches, pains and headaches (49).
😐 Insomnia & Depression: a co-occurrence
Insomnia may cause depression and depression may cause insomnia; the direction is unclear. But, evidence suggests depression is 10 times more likely to occur in insomniacs (50).
😴 Sleep disturbance can predict psychiatric disorders
Sleep is linked to most psychiatric disorders and can emerge years before a diagnosis such as bipolar disorder (51).
🥜🍐 Eating all the time
Insufficient sleep makes us hungrier. It changes the neuroendocrine system which controls appetite. In a lab experiments, people who are sleep deprived tend to keep meal portions the same but snack late into the night eating around 130% of their daily intake with around 500 of these calories consumed late at night (10, 52) . Outside the lab, an app based experiment where dieticians analysed food photos, confirmed this sleep-snacking link (53).
🍩 What we want to eat changes.
Sleep deprivation changes food preference. Brain scans show increased activity in reward pathways even when well nourished, making high energy food more appealing (54).
Obesity and sleep exist in a vicious cycle. Staying up late increases calorie consumption but doesn’t use much energy – around 17 kcal/ hour or half a biscuit over three hours (10, 55). Short sleepers were found to have a 45% increased chance of developing obesity which in turn disrupts sleep (10, 52, 56).
👨🏿👩🏻 Who you are can change risk of weight gain
Short sleep may make men more prone to gaining more weight than women and people of African American heritage may be more likely to gain weight than Caucasians. This was discovered following the same sleep restriction of four hours sleep for five nights (52) And, people of Black and Hispanic origin are more likely than people of Caucasian heritage to get less than 6 hours sleep a night, increasing health risks (57)
❤️ Sleep deprivation is associated with poor heart health
Sleeping too much or too little is associated with heart disease and stroke. Increased activity in the nervous system may be the mechanism by which this physiological change occurs as it is associated with diabetes, heart disease and hypertension (42).
🌡Diabetes Type II
Poor sleep quality poses a diabetes type II risk of a similar scale to obesity, family history and low physical activity (58). Short sleep, difficulty falling asleep and difficulty staying asleep increase diabetes type II risk by 28%, 57% and 84% respectively(59). This may be because these sleep disorders are associated with decrease of insulin sensitivity without compensation from a sleep dependent beta cell.
Diabetes may be treated in future by prolonging slow wave sleep. We know this because reducing healthy people’s slow wave sleep for just three nights reduced insulin sensitivity by 25%, causing reduced glucose tolerance(60).
🔬Poor sleep quality may speed up ageing of gene protectors
In humans, people with better sleep quality show less ageing in their telomere length compared to those with less sleep (61). Telomeres protect molecules from deterioration.
So how can we engineer better sleep?
We can engineer sleep habits from the moment we wake up. These can teach the body when it’s bedtime and protect the quality of the sleep we have.
Sleep hygiene uses our reliance on habit to build routines which train our circadian rhythms for sleep. Surrounding ourselves with ‘zeitgebers’ – environmental cues like books in the bedroom facilitates sleep onset (62). Routine functions by conditioning part of our brain called the suprachiasmatic nucleus (SNC) to prepare for and induce sleep.
☀️Get enough daylight
Exposing ourselves to natural light in the day, for example walking on a lunch break, helps sleep onset at night. Melatonin release works like an elastic band; the more we suppress it by getting outside in the day and evening, the more it rises in the dark to promote sleep (7).
💡Avoid light after dark
Overexposure to light, in particular electric lighting, late at night disrupts our sleep promoting melatonin levels meaning we feel less tired, particularly so for women!(63)
💻 Avoid blue light for the hour before bed
Blue and high intensity light before bed delays sleep onset and disrupts quality of sleep, making it less efficient and less able to process glucose (64). LED lights, tablets and smart phones have this blue high energy light.
📺 LCD screens use different light so can help ruminators
LCD screens have a flatter light so can help people who struggle from anxiety and struggle to switch off.
🌮 Eat early to extend the overnight fast for a higher metabolism
Try to avoid late night snacking to improve sleep onset and boost your metabolism (53).
⛔️ Resist staying up late
As 24 – 25 hour humans in a 24 hour world, we tend to want to stay up a bit later each night and wake up later. Using natural light helps to keep us in synch with planet Earth (23, 24).
The hypothalamus is part of the brain home to sleep promoting cells; and GABA is the lead neurotransmitter which can turn off wake promoting cells. Insomnia medication includes GABAa agnoinists to encourage the onset of sleep(65).
👨⚕️Shift work & Transcontinental travel
We can minimise shift work disruption by engineering our light environments. Sleeping in the evening before a night shift and using bright lights at work suppresses sleep hormone melatonin (9).
Sleep is so important for sustainable health and wellbeing. Poor sleep can cause neural biological changes which impact the health of our whole bodies – mental and physical. Acknowledging the importance of sleep and what might be preventing us from getting enough of it can foster practical rest protective habits that work for us.
If you are struggling to fall asleep, talk to your doctor. Worrying about sleep onset can make it harder to fall asleep and addressing it is important to help feel more like you!
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