During our early years evolving as a species, sleep was when we were most vulnerable to predation. Sleep was also when we were not hunting or gathering nutrition or when we were not mating for reproduction. Essentially, sleep is counterintuitive from an evolutionary standpoint and should have been selected against long time ago. Yet, it has been preserved as a core biological behaviour. Human beings can last several weeks without food, several days without water. But we won’t last more than a few days without sleep. No wonder sleep deprivation is a torture (it literally is – it’s one of the most brutal torture techniques used against prisoners). There must be an important reason for why that is because, evolution, otherwise, is super-effective in weeding out behaviours which are anti-selection - Selection from a Darwinian Natural Selection point of view.
That reason is the fact that sleep is when we recover and recharge. Sleep is when our bodies can recover from the inflammation caused by a whole day of eating and digesting and physically tiring ourselves. It's when our immune system can fight against pathogens. It’s when our stress levels and correspondingly our heart rate and blood pressure naturally go down. Sleep is also when our brain gets cleansed of all the gunk in the form of unwanted proteins that can impair brain function, cause neuroinflammation and can hamper memory formation.
It is important to get good sleep as it resets the ability to be alert, focused, and emotionally stable in wakeful periods. Sleep plays an important role in several brain functions, including how the nerve cells (neurons) communicate with each other.
Unfortunately, our duration and quality of sleep are going down. In the last few decades alone, we have reduced our average sleep duration from 8 hours to 7.5 hours. Relative to our millions of years of sleep duration more than 8 hours, that’s a very rapid deterioration.
Research shows that it affects every tissue and system of our body from the brain, heart, and lungs to metabolism, immune function, mood, and disease resistance. Poor quality and chronic lack of sleep results in increasing the risk of disorders including high blood pressure, cardiovascular disease, diabetes, depression, and obesity.
What governs sleep?
It is governed by two forces, chemical, and circadian. Adenosine is an important component of chemical force. It is a molecule in the nervous system that builds up the longer we are awake, creating sleep drive or sleep hunger. Sleepiness is driven by an increase in adenosine levels. Caffeine acts as an adenosine antagonist. It binds to adenosine receptors, and results in the receptors not binding to adenosine which would have caused sleep.
Circadian forces work in a 24-hour cycle determined by sunrise for the most part but also by other physiological activities such as eating and drinking, exercise, and exposure to other sources of bright light. When we wake up around the time of sunrise, adenosine is low. Adrenal glands release Cortisol and Epinephrine which stimulates the release of adrenaline in the brain which wakes us up. Normal healthy rise of cortisol occurs early in the morning which sets a timer in the body and nervous system. In early morning, the retina is not very sensitive; hence it requires many photons to activate the mechanism, which we get from sunlight. It inhibits the pineal gland from releasing melatonin and darkness stimulates the pineal gland for releasing melatonin. Melatonin is the sleep-causing and regulating hormone.
Insulin (like caffeine) is a powerful melatonin antagonist which means it inhibits the effect of melatonin. This is the reason why we can stay awake for longer during exam nights or hackathons by eating pizza or other insulin-stimulating junk food or by drinking coffee. This is also why we must eat our dinners at least 3 hours before bedtime. On the contrary, good carbohydrates derived from fiber rich whole grains, vegetables, legumes, and beans are great for sleep because they promote the production of serotonin which is the calming neurotransmitter.
Lastly, alcohol is terrible for sleep. Even though, it might make us fall asleep, but it hampers the quality of sleep by stopping our brain from functioning naturally during sleep. It knocks us out quickly but it also wakes us up several times during sleep because it’s a diuretic which means it dehydrates us and makes us pee more. This dehydration coupled with bad sleep is the primary cause of hangovers.
Basics of sleep
There are two types of sleep - Rapid Eye Movement (REM) sleep and Non-Rapid Eye Movement (Non-REM) sleep. REM sleep is also known as paradoxical sleep because the brain is active while our body is paralyzed. The activity of eyes and muscles are determinants of REM sleep. Before going into REM sleep, the brain stem sends a signal of paralysis to alpha motor neurons in the spinal cord which controls voluntary skeletal muscles. Two voluntary muscles that do not get paralyzed are the ocular muscles and inner ear muscles. REM sleep is a major predictor of longevity. A 5% decrease in REM sleep is related to a 13% increase in the risk of mortality.
Non-REM sleep is subdivided into four stages – stages 1 & 2 known as Light non-REM sleep whereas stages 3 & 4 are known as Deep non-REM sleep. During the progression of sleep stages, the heart rate drops, brainwaves are not stable, and muscle tone drops. The first cycle of sleep which is the first 90 minutes is deep non-REM sleep, and Second cycle of sleep, 90 minutes are stage 2 non-REM sleep. Heart rate, insulin regulation is Non REM sleep-dependent, whereas growth hormone, testosterone is REM sleep-dependent.
How does sleep deprivation cause inflammation and chronic disease?
Inflammation in short is our body's natural mechanism against damage and injury. It is activated primarily by our immune system which activates white blood cells that produce cytokines and other inflammatory molecules that attack pathogens. So, imaginably, acute inflammation against external invaders is great because that's how our body protects itself. But, if inflammation doesn't subside, it becomes chronic inflammation and that is not good because it contributes to developing heart disease, diabetes, stroke, cancer, and Alzheimer’s disease.
Here's how lack of good sleep contributes to inflammation. The first pathway is in our blood vessels. When we sleep, our blood pressure goes down and our blood vessels dilate. When we don't sleep properly and not for 7-8 hours, our blood pressure doesn't go down and our arterial walls harden. These cells then trigger inflammation which leads to increases in inflammatory molecules such as cytokines, interleukin-6, C-reactive protein (that’s elevated in people at risk for heart disease and diabetes). The second pathway is by increasing our stress levels which means our cortisol and our epinephrine levels don't go down as they should. These hormones also keep our blood pressure high.
Lack of sleep also impacts our brain function and causes inflammation in the brain. When we sleep, our glymphatic system takes over and does the cleaning up job in the brain by flushing our brain with cerebrospinal fluid. This cleaning up job removes the beta-amyloid protein that injures our nerve cells and impairs brain function. When this protein does not get cleaned up due to lack of sleep, inflammation builds up. This cocktail of inflammation and beta-amyloid build up causes cognitive decline, dementia and even Alzheimer's.
What should we do to enhance sleep?
We must target at least 7.5 hours of sleep every night with no interruptions and we should sleep early in the night instead of later in the night because our ratio of REM sleep to non-REM sleep is higher when we sleep early. REM sleep is the most beneficial to our brain and body – so, we should try to maximize that. Below are a few steps to enhance sleep:
1. Avoid
Caffeine and nicotine late in the day, at least 8 hours before bed. You can have green tea or chamomile or other non-caffeinated beverages
Too much alcohol before bed. If you are drinking, don’t exceed 2 drinks and preferably, drink those with some high fiber foods
Looking at your phones or other electronic devices at least an hour before going to bed. This is not only for avoiding the blue light that hampers melatonin but also for avoiding sensational news and content that can prevent us from calming down for sleep
Bright light, especially blue light in the evening hours
Eating dinner at least 3 hours before sleep and try to eat plant-based, whole foods to get the good carbohydrates for keeping us full and for producing serotonin in the brain for feeling calm
Using the bed you sleep on for lounging or for working or for daytime reading. Our brain is very good at making subconscious associations and will associate the bed with these other activities and prevent us from falling asleep
Drinking too much water before 2 hours of going to sleep. It can cause urination which can disrupt sleep.
Taking naps during the day as that can lower our adenosine levels and prevent us from falling asleep in the night. If you are tired during the day, practice NSDR (Non- sleep deep rest) such as Meditation or Yoga Nidra (lying in bed with eyes closed listening to slow wave, deeply relaxing music)
Taking melatonin supplements because it affects our natural production of melatonin in the body and because it affects several other hormones in the body. Please consult your doctor if you must take these supplements
2. Practice
Consistency in your sleep routine. It’s best to stick with our sleep time and wake up time every day because our brain likes consistency
Meditation because it calms down the sympathetic nervous system which agitates us. Meditating for 10-20 min before sleep can enhance the quality of sleep
Getting 30-40 minutes of natural sunlight daily. Exercise and sunlight are both important for circadian rhythm alignment. Getting 10 min of sun early in the morning can set our waking up clock and getting 10 min of setting sun in the evening can set up on sleep-causing clock
Exercising 30 minutes a day but no later than a few hours before going to bed
Relaxing before bed – try a warm bath, reading, or another relaxing routine
3. Our thyroid hormone imbalance can also affect our sleep by making us too sleepy during the day or by keeping us awake in the night. So, if you are struggling with these symptoms, please also check your thyroid levels
References:
● Dr. Matthew Walker: The Science & Practice of Perfecting Your Sleep https://www.youtube.com/watch?v=gbQFSMayJxk
● Master Your Sleep & Be More Alert When Awake https://www.youtube.com/watch?v=nm1TxQj9IsQ&t=3482s