What is sleep?
We go to bed, lie there, lose consciousness for a few hours, and then wake up. That’s how most of us have known sleep, as a passive event in our lives where our brain and body do nothing. But in fact, sleep is not the absence of wakefulness it is more active than we think. When they measured the brain activity during sleep it resembles what you see below. Don’t worry, we’ll get into the difference between NREM and REM sleep later on.
What drives our sleepiness or wakefulness
Your brain doesn’t decide by itself that it’s enough Netflix now, we’re going to sleep. It needs inputs and stimuli and when it comes to sleep there are two main ones: sleep pressure and sunlight.
Light and circadian rhythm
The photons we get either from the sun or from artificial light are essential for our brain to reset its circadian clock. What’s the circadian clock.
It’s our body’s internal pre-determined clock called the suprachiasmatic nucleus. It’s centred in the brain and communicates the “time” to almost every organ in the body. This 24h rhythm is referred to as the circadian rhythm (circa= around and dian = day).
A lot of people who know about the existence of the circadian rhythm believe that it is caused by the sun’s rising and setting. But it turned out it’s not completely the case. In experiments where humans were in an environment where they couldn’t see the changes in light, they still kept an internal clock that was not exactly 24h but varied around that. The sun however is necessary to reset the inaccuracy of this internal clock to make it around 24h cycle as we know it.
The way your brain clock communicates to the rest of the brain and body that it’s time to sleep is by releasing a hormone called Melatonin. This hormone does not help you during sleep, but it’s crucial to start the event of sleep.
Sleep pressure
Sleep pressure is the build-up of a chemical called adenosine in your brain. The more you are awake, the more adenosine gets accumulated and the sleepier you get.
The graph below shows the interaction between the circadian rhythm (process C) and the sleep drive (Process S). The bigger the distance between the two, the greater the urge to sleep is.
They both play a huge role in recalibrating our sleep need and wakefulness feelings . besides, having all of these things will help initiate sleep better.
Besides, having these two factors will determine how sleepy or non sleepy you will feel throughout the day.
Sleep structure
Our sleep is divided into cycles depending on how long it is. If you sleep from 11 pm to 7am (Around 8h duration), you’ll have 5 cycles in total with each cycle lasting around 90mins. In these cycles we alternate between two main stages of sleep:
- REM: (Rapid Eye Movement): where the brain activity is almost identical to when we’re awake and the eyes would move fast under the eyelids
- NREM: (Non-Rapid Eye Movement): where the eye movements and brain waves would become calm. They are divided into 4 other stages of sleep, from stage 1 to stage 4. In each stage, the sleep is deeper than the other with depth being how difficult it is for you to be woken up.
In the first half of the night, the majority of those 90 minute cycles are comprised of a lot of deep non REM sleep and in the other half we switch to lighter REM sleep where dreams happen.
REM helps us recalibrate and fine-tune our emotions while NREM sleep helps us take newly learned information into long-term memory.
We get a split of 20/80 between REM et NREM sleep. Below, an example of a perfect sleep architecture:
Night Owls and Early birds, do they exist?
If you don’t know the difference between early birds and night owls. The first ones wake up easily earlier in the day but struggle to stay asleep later, and the latter is the exact opposite. This difference has actual biological existence and is referred to as chronotype.
Chronotype is strongly determined by your genetics. If your parents are night owls, you’ll most likely be a night owl as well. Sadly, our society rewards the early birds and unfairly treats the night owls. And the rhythm of modern society is set up to suit early birds as well.
Coffee and sleep
Caffeine works by blocking the adenosine receptors in your brain which stops you from feeling fatigued. When you consume it, the levels of circulating caffeine peak at around 30min after you consume it.
Same as any drug, we characterise caffeine by its half-life, which is the time needed to clear 50% of the concentration. It is evaluated at around 5 to 7 hours. Caffeine gets removed from our system by an enzyme secreted by the liver. And its efficiency varies among people and is mainly due to genetics. This is why some people cannot sleep even if they drank their coffee early in the morning and some drink it before bed and sleep just fine.
It is important to note, that even if you feel like you’re getting to sleep just fine if you drink coffee close to your bedtime. It has been shown that the architecture of sleep that actually determines the quality of your sleep may be disrupted.
How much sleep should we get?
The National Sleep Foundation’s sleep recommends that adults get between 7 to 9h of sleep.
Why do we sleep and the dangers of a lack of sleep.
Why we sleep
- One of the main advantages of sleep is memory consolidation. When we go about our day our brain picks up new information and stores it in the hippocampus which has a very limited storage capacity. Once it reaches its limit, the brain is no longer able to store more and can even overwrite some. When we sleep, we help empty the hippocampus by putting all the stored information in our permanent brain storage space.
- Through REM sleep we recalibrate our emotional brain circuits allowing us to navigate the next day’s psychological challenges easier and if you dream it helps the brain meld our past and present knowledge which will make you more creative
- Sleep is like a reset button for your body. It reforms the body’s metabolic state by regulating insulin and blood circulating glucose, helps us maintain a diverse microbiome within our guts.
Why we should not, not sleep:
- Impaired immune function
- Increased risk of TypeII diabetes, heart disease, obesity and alzheimers
- It just makes you irritable, moody and affects your quality of life.
Why do we dream
I’m sorry to disappoint, but until now we do not have a clear answer to why we dream. There are various theories and debates among sleep scientist but there are no strong evidence yet to be able make a clear statement. Since dreams happen mostly in the REM stage of sleep, we can by association say that they offer the same benefit as REM.
Is sleep debt recoverable
If for some reason you weren’t able to respect the recommended 7h to 9h, can you make up your sleep debt by sleeping it another night ? If the debt is about 1h, research has shown that it can take up to four days to recover from it and up to nine days to eliminate sleep debt. Unlike popular belief, a quick 20min nap cannot make up for it.
How to optimise our sleep
One of the best ways to optimise our sleep is to have a good sleep hygiene. Having it as routine will help you have a consistently good sleep. Here are some tools to help you optimize your sleep:
Before bed:
1- During the evening, after sunset, limit your exposure to bright light. Not only blue light by wearing your blue light blockers, but all artificial lights. At night we tend to be more sensitive to light
2- Try to have complexe carbohydrates in your last meal. Carbs, although demonized a lot, play a huge role in the production of the happy hormone serotonine which is a precursor to the hormone melatonin that helps initiate sleep.
3- The higher your body temperature the more alert you are and vise versa. Having a warm shower or a bath is great addition to helpsyour core body temperature drop which will make you calmer and more relaxed.
5- Avoid caffein alltogether (unless it’s a real emergency)
6- Keep the room you sleep in cool and completely dark
After waking
1- View sunlight as soon as you wake up. This helps reset your circadian clock. If the sky is clear try do it for at least 10mins, if its a slightly covered sky for 20min and if completely covered try to shoot for 30 to 40 mins. If you wake up before the sunrise, turn on artificial lights and get the sunlight as soon as it rises.
2- Have a cold shower or exercise. This will raise your core body temperature making your more alert which will lead you to:
3- Avoid coffee before the 90min after your wake up time. If you drink it before, you’ll interfere with your body’s natural cortisol rhythm and will make you crash in the afternoon.
During the day
1- Try to get some sunlight in your eyes especially when it is at lower solar angle (starts descending). This helps remind your circadian clock, that it’s evening time and we’re nearing sunset. How does the brain know the difference between morning light and evening light you may say ? Well, they have different wavelengths which are detectable by your brain.
2-Determine your caffein cut off hour which is around 8-10 hours before bedtime for most people to ensure that most caffeine is cleared out from your system.
3- Naps are really effective at resetting your energy levels. However, if you have trouble sleeping at night they are not recommended. They will interfere will sleep pressure by reducing it and making it harder for you to fall asleep at night. But try to keep them to less than 90min
RESSOURCES:
- Why we sleep “Mathew Walker”
- Recommendations for daytime, evening, and nighttime indoor light exposure to best support physiology, sleep, and wakefulness in healthy adults: https://journals.plos.org/plosbiology/article?id=10.1371/journal.pbio.3001571
- Sleep and immune function. Pflugers Archiv : European journal of physiology, 463(1), 121–137. doi:10.1007/s00424-011-1044-0 https://www.ncbi.nlm.nih.gov/pubmed/22071480
- Elevated ghrelin predicts food intake during experimental sleep restriction. Obesity (Silver Spring, Md.), 24(1), 132–138. doi:10.1002/oby.21321 https://www.ncbi.nlm.nih.gov/pubmed/26467988
- The National Sleep Foundations sleep time duration recommendations: methodology and results summary. Sleep Health (2015) http://dx.doi.org/10.1016/j.sleh.2014.12.010
- Sleep-dependent memory consolidation.https://pubmed.ncbi.nlm.nih.gov/16251952/
- Sleep toolkit: tools for optimizing sleep & sleep-wake timing: https://www.youtube.com/watch?v=h2aWYjSA1Jc&t=2821s
- #221 ‒ Understanding sleep and how to improve it: https://peterattiamd.com/understanding-sleep
