Why we sleep - review and podcast!

This month I have a slightly longer blog. I recently read Why We Sleep by Dr Matthew Walker, and I felt I had to share it with you. This blog contains direct quotes and paraphrases from the book; they are not my own words. I hope to give you an overview and highlights from the book to apply to your health. If sleep makes you anxious, you may wish not to read this blog, as I would not want to heighten that. If you would prefer to listen I have recorded a podcast to listen please click here.

Let’s start at the beginning.

What causes sleep?

Two factors cause us to sleep, our circadian rhythm and sleep pressure.

You may have heard your circadian rhythm referred to as your internal 24-hour clock. This 24-hour clock is controlled by your suprachiasmatic nucleus, sitting just above the crossing point of the optic nerves. It samples light signals to determine day and night, which it communicates to the rest of the body via the hormone melatonin. It is the master clock keeping all your biological clocks in time, regulating our biological function over 24 hours, keeping us alert and awake during daylight hours and asleep during the night.

Secondly, sleep pressure. Sleep pressure is dependent on the chemical adenosine. Adenosine concentration increases with every waking minute, simultaneously turning down wake-promoting areas and increasing sleep-inducing regions, increasing your desire to sleep. Concentrations reach a peak around 12-16 hours of being awake, sending you into a deep slumber. Over the night, the brain degrades the adenosine, a process that takes roughly 8 hours to complete—leaving you feeling refreshed the following morning.

So, my internal clock and building sleep pressure are telling me to sleep. But is it necessary?

Why do I need sleep?

During sleep, humans cycle through a mixture of two completely different types of sleep. NREM (non-rapid eye movement ) and REM (rapid eye movement ). Each with different but equally important purposes.

NREM sleep extracts and removes the unnecessary neural connections while moving important information into long-term storage. REM sleep strengthens the valuable connections that remain and forges creative novel connections. These processes occurring during REM and NREM sleep enhance our memory, learn and process new information, and problem-solve.

Although NREM sleep is just as essential, I would like to talk more in-depth about the REM stage of sleep.

Have you ever woken up with the solution to a problem that has been bugging you for a while?

Or found resolve the following day to an unpleasant emotional experience?

You have REM sleep to thank.

 REM sleep allows us to build connections between distantly related information that are not obvious in the light of waking day—taking information from past experiences and applying it to recent problems to find new solutions.

 Furthermore, when we enter REM sleep, the brain enters unique neural chemistry. The stress-producing hormone noradrenaline is completely shut off, creating a stress-free environment for the brain, allowing us to recall our experiences without bitter emotion and offering an emotional resolution. For this reason, we can recall a traumatic memory without reliving the same distressing emotional response. We also need REM sleep for our daily emotional stability. REM sleep recalibrates and fine-tunes our emotional circuits every night, allowing us to respond rationally. Dr Walker’s study on healthy adults found that the unslept brain had a 60% increase in emotional reactivity, swinging between extremes of emotions.

 Without a good night's sleep, you do your body damage.

 Heart disease, obesity, dementia (Alzheimer’s), and diabetes, some of the leading causes of disease and death in developed nations, all have recognised causal links to lack of sleep.

Alzheimer’s

 In patients with Alzheimer’s, there is a toxic form of the protein beta-amyloid, which kills surrounding brain cells. Lack of sleep increases the amount of this toxic protein in the brain.

 Cardiovascular disease

 When we lack sleep, our sympathetic nervous system is overactive—leading to increased heart rate and blood pressure, factors related to an increased risk of cardiovascular disease. A systematic review and meta-analysis of available studies totalling almost half a million participants found that sleeping 5–6 hours per night was associated with more than a 45% greater risk of fatal and non-fatal coronary heart disease and a 15% greater risk of stroke.

 Diabetes and weight gain

When we are sleep deprived, our cells become less receptive to insulin and consequently do not efficiently absorb glucose—increasing glucose levels in the blood. Chronic sleep deprivation is now recognised as one of the significant contributors to the escalation of type 2 diabetes throughout first-world countries.

Lack of sleep increases hunger and appetite due to decreased levels of the hormone leptin, the appetite blunter, and increased levels of ghrelin, the hunger hormone. Increasing food consumption but not leaving us satisfied. Couple this with diminished impulse control, and we, unfortunately, have the recipe for weight gain.

Immune system

Many people realise the association between being tired and run down and catching a cold. We have a weakened immune system. But may not realise the extremity. Sleeping 5 instead of 7 hours on average a week can increase the infection rate from 18 to 50%. Considering that the common cold, influenza, and pneumonia, all infectious diseases, are among the leading causes of death, you may consider getting a good night's sleep.

So, getting a good night’s sleep can enhance your memory, help you solve problems, and be less irrational. As well as lower your food cravings, protect you from dementia, ward off colds and flu and lower your risk of heart attack and stroke. It is potentially helping you to live a longer, healthier life.

Yet, after all these benefits, in general, we as humans do not prioritise sleep. In the UK, 39% of all adults report sleeping less than 7 hours, with an average night sleep of 6 hours and 49 minutes.

This is not enough.

How much sleep do I need?

The recommendation by the National Sleep Foundation is 7-9 hours’ sleep duration for healthy adults (ages 18-65), and a mean of 8 hours sleep. Further supporting this is the work done by Dr Van Dongen and colleagues, who calculated that the amount of sleep necessary to prevent neurocognitive impairment was 8.16 hours.

 However, this doesn't necessarily mean going to bed at ten and waking up at six is going to get you all the sleep you need. It is improbable you will be asleep for all that time. A healthy individual will have a sleep efficiency of 85%. Therefore, to get even the minimum sleep duration of 7 hours, you will need to give yourself a sleep opportunity, or time in bed, of 8 hours and 15 minutes. Further, to get a total of 8 hours of sleep, you would need a sleep opportunity of 9 hours 12 minutes. So, we should be aiming to spend 9 hours in bed sleeping a night.

 You may feel there is no way possible you have enough time in the day to sleep that long. However, Dr Walker believes you should give even more time to sleep. Studying the small enclaves of Greek islands over six years found that abandonment of regular siestas caused a 37% increased risk of death from heart disease relative to those who took a nap. In fact, in working men, mortality increased by over 60%. Note that none of these individuals had a history of heart disease at the beginning of the study. For this reason, Dr Walker believes we should follow a biphasic pattern of sleep, still getting out 7-8 hours of sleep a night but followed by a 30–60-minute nap in the afternoon. These islands’ practice of biphasic sleep and the healthy diet has given rise to names such as: where people forget to die.

The lucky 0%

Many individuals proclaim they only need 5-6 hours’ sleep. You may claim to be one of these. Some of you may be telling the truth. Dr Walker and colleagues have found a group of people that can survive on 6 hours of sleep without any impairment. However, you would be fortunate so lucky in the fact that his colleague Dr Thomas Roth quotes  ‘the number of people who can survive on 5 or 6 hours sleep without any impairment expressed as a percentage to a whole number is 0%’. Not impossible, but very rare. This is due to a rare gene, the BHLHE41.

Night owls and morning larks

Science says they are true. Some people really cannot get up in the morning, and some people really cannot stay up late. It is unavoidable DNA hard wiring. As discussed, all individuals have this internal 24-hour clock. However, the peaks and troughs are different from one person to the next. Meaning some people's peak wakefulness arrives earlier than others, and some people’s sleepiness arrives later than others. Lending itself to morning people, about 40% who prefer to wake up around dawn. And evening people, about 30%, naturally prefer going to bed late and subsequently waking up late the following morning. The remaining 30% are somewhere in the middle.

What happens when we don’t get enough sleep?

Adenosine concentrations remain too high, like a debt. Come morning, some of yesterday’s adenosine remains. You will carry this sleepiness through the next day, and this continues to roll over to the next sleep and the next and the next.

One of Dr Walker’s biggest take-homes from the book is that you cannot sleep back sleep that you have lost. You do not recover your precious NREM and REM sleep. The previous study found that after ten nights of 6 hours of sleep, even after three nights of recovery, sleep performance did not return to that observed at the original baseline to those getting a total of 8 hours of sleep. Nor did any group recover all the sleep hours they had lost.

How can I tell if I need more sleep?

Dr Walker suggests the two main questions you should ask yourself are:

-        After waking up, could you fall back asleep at 10/11 am?

-        Can you function optimally without caffeine before noon?

These may suggest you are sleep deficient. You should give yourself a sleep opportunity of at least 9 or 8 hours in bed. If you are still finding yourself tired every day, you should consider seeking help for a sleep disorder. He is firmly against sleeping pills. Rather than inducing a natural sleep, sleeping pills knock us into an unconscious-like state. You do not get a restorative sleep with the benefits of natural sleep. And you are likely to start a dependency cycle.

What’s stopping you from sleeping?

Modern light

Artificial evening light, especially blue light, suppresses the secretion of melatonin, the hormone that regulates sleep/wake cycles, fooling your suprachiasmatic nucleus into believing the sun has not yet set. Compared to reading a printed book, reading on an iPad delayed the rise of melatonin by 3 hours. Even more worryingly, individuals lost significant amounts of REM sleep.

Alcohol

Alcohol is a sedative; it may seem to help you drift off to sleep. However, it does not send you into a natural sleep. The brainwaves that are seen when asleep after alcohol are more akin to a light form of anaesthesia. That precious REM sleep is suppressed, and your sleep becomes fragmented, leading to an un-restorative sleep.

Temperature

Your nocturnal melatonin levels are not just controlled by loss of daylight but also drop in temperature. For your body to successfully initiate sleep, your core body temperature must decrease by 2-3 degrees. The ideal temperature to sleep at is 65 degrees Fahrenheit or 18.3 degrees centigrade. As we don’t all have the luxury of temperate control, what else can we do?

Body temp is controlled by your hands, feet, and head. Warm these areas to draw out heat trapped in the body’s core, such as taking a hot bath. Studies found a hot bath before bed induces 10-15% more deep NREM sleep in adults.

Caffeine

Remember, sleep pressure caused by increasing adenosine concentrations creates the urge to sleep. Caffeine blocks the adenosine receptors on the brain. Stopping the build-up of adenosine concentration and therefore blocking signals urging the brain to sleep, tricking your brain into full wakefulness. Caffeine has a half-life of 5-7 hours; that is the time to get rid of 50% of the ingested caffeine. Meaning that if you were to consume caffeine in the afternoon, it would still be in your system and affect your ability to sleep later that evening.

So, I leave you with these 12 key tips for a good night's sleep recommended by Dr Walker from the National Institute of health. 

1. Stick to a sleep schedule

We should aim to go to bed and wake up at the same time each day. Sleeping later on weekends won't entirely make up for lack of sleep during the week and will make it harder to wake up Monday morning. Dr Walker emphasises this is the #1 priority from the list; stick to a regular sleep schedule.

2. Don’t exercise too late in the day

Exercise is great, and we should try to exercise at least 30 minutes on most days. But try to time it no later than 2-3 hours before bed.

3. Avoid caffeine & nicotine

Colas, coffee, teas (that aren’t herbal), and chocolate contain caffeine, a stimulant. Even consuming these in the afternoon can affect your sleep. Nicotine is also a mild stimulant, and smokers will often wake up earlier than they would otherwise due to nicotine withdrawal.

4. Avoid alcoholic drinks before bed

The presence of alcohol in the body can reduce your REM sleep, keeping you in the lighter stages of sleep.

5. Avoid large meals and beverages late at night

A light snack before bed is okay, but a heavy meal can cause digestive issues, interfering with sleep. Drinking too many fluids can cause frequent awakenings to urinate.

6. Avoid medicines that delay or disrupt your sleep (where possible)

Some commonly prescribed heart, blood pressure, or asthma medications, as well as some over-the-counter and herbal medicines for coughs, colds, or allergies, can disrupt sleep patterns. If you have trouble sleeping, it may be worth speaking to your doctor or pharmacist to see if any of the drugs you're taking may be contributing to this. It may be possible to take them earlier in the day.

7. Don’t nap after 3 pm

Naps are great, but taking them too late in the day can make it hard to fall asleep at night.

8. Make sure to leave time to relax before bed

It’s important to have time before bed to unwind. Try to schedule your days so that there is time to relax before bed. A relaxing activity such as reading or listening to music should be part of your schedule.

9. Take a hot bath before bed

The drop in body temperature after a bath may help you feel sleepy, and the bath can help you slow down and relax before bed.

10. Have a dark, cool (in temperature), gadget-free bedroom

We sleep better at night if the temperature in the room is kept on the cool side. Gadgets such as mobile phones and computers can be a distraction. Additionally, the light they emit, especially the blue light, suppresses the secretion of melatonin.

11. Get the correct sunlight exposure

Daylight is key to regulating daily sleep patterns; you should try to get outside in the natural sunlight for at least 30 minutes per day.

12. Don’t stay in bed if you (really) can’t sleep

If you find yourself still in bed for more than 20 minutes, or you’re starting to get anxious in bed, get up and do something else until you feel sleepy. Anxiety whilst trying to sleep can make it harder to fall asleep.

"Add life to your years & years to your life."

Written by Hope Parish.

References

1.     https:///www.nlm.nih.gov/medilineplus/magazines/issues/summer12/articles/summer12pg20/htm.

2.     Van Dongen, H. P., Maislin, G., Mullington, J. M., & Dinges, D. F. (2003). The cumulative cost of additional wakefulness: dose-response effects on neurobehavioral functions and sleep physiology from chronic sleep restriction and total sleep deprivation. Sleep, 26(2), 117–126. https://doi.org/10.1093/sleep/26.2.117

3.     How Much Sleep Do We Really Need? | Sleep Foundation

4.     Prather, Aric & Janicki-Deverts, Denise & Hall, Martica & Cohen, Sheldon. (2015). Behaviorally Assessed Sleep and Susceptibility to the Common Cold. Sleep. 38. 10.5665/sleep.4968.

5.     Francesco P. Cappuccio, Daniel Cooper, Lanfranco D'Elia, Pasquale Strazzullo, Michelle A. Miller, Sleep duration predicts cardiovascular outcomes: a systematic review and meta-analysis of prospective studies, European Heart Journal, Volume 32, Issue 12, June 2011, Pages 1484–1492, https://doi.org/10.1093/eurheartj/ehr007

6.     Reeves, B. C., Karimy, J. K., Kundishora, A. J., Mestre, H., Cerci, H. M., Matouk, C., Alper, S. L., Lundgaard, I., Nedergaard, M., & Kahle, K. T. (2020). Glymphatic System Impairment in Alzheimer's Disease and Idiopathic Normal Pressure Hydrocephalus. Trends in molecular medicine, 26(3), 285–295. https://doi.org/10.1016/j.molmed.2019.11.008

7.     Lack of Sleep Disrupts Brain’s Emotional Controls | National Institutes of Health (NIH)

8.     2013 International Bedroom Poll | Sleep Foundation

9.     Walker.D (2018) Why we sleep. 1st ed. Penguin books.