Sleep Essentials
Sleep is the most conserved physiological state among all animals, with humans spending roughly one-third of their lives sleeping. Learn all the basics of sleep in this article.
Many of us never really thought of it, but on average, we spend around one-third of our lives sleeping. That’s a massive amount! We invest more overall time into sleeping than any other essential activity, such as eating or drinking water. We are not the only ones in nature being so dedicated to sleep, but basically, all animal species exhibit sleep or sleep-like states. This makes sleep the most evolutionary conserved activity across the animal world.
Why Do We Sleep?
Despite enormous research conducted on sleep during the last decades, its biological purpose remains a mystery.
Sleep is beneficial for basically all systems in our bodies. Our brain and nervous system carry on a self-cleaning routine during sleep, removing toxins and waste products through the blood circulation and a special fluid that surrounds the brain and the spinal cord, known as cerebrospinal fluid. At the same time, our cardiorespiratory system slows down, with the heart rate and breath dropping to a minimum.
Chronic lack of sleep is extremely detrimental to general health, leading to an increased risk of all-cause mortality. A very prolonged lack of sleep is even lethal. Some studies performed on rodents showed that, when the animals were not allowed to sleep at all, they all died after about two weeks (1,2).
Biology Of Sleep: How Do We Fall Asleep?
We possess a tightly regulated sleep-wake system, which also goes under the name of the circadian rhythm. Everything starts at the DNA level, where certain genes are turned on or off depending on entering and maintaining sleep or wakefulness. In 2017, Jeffrey C. Hall, Michael Rosbash, and Michael W. Young were awarded the Nobel Prize in Physiology or Medicine for “for their discoveries of molecular mechanisms controlling the circadian rhythm”, a milestone in better understanding the genetic processes underlying our sleep-wake system (3).
Multiple regions of the nervous system are involved in transitioning into the sleep stage, starting from a brain area called the hypothalamus. Through our eyes, we send signals to the brain depending on light exposure, either natural or artificial light. When the night comes and we turn off the lights in our room, our eyes perceive darkness and they send these signals to the hypothalamus which, together with the brain stem region, starts producing a neurotransmitter known as GABA. GABA is the major inhibitory neurotransmitter in the nervous system, reducing nervous activity and inducing relaxation. Such neurotransmitter works synergistically with melatonin, a crucial hormone in the sleep-wake cycle. Melatonin is produced and secreted by the pineal gland, a very small region located in the middle of the brain, upon stimulation by the hypothalamus. All these perfectly coordinated processes induce us gradually into sleep (4).
Sleep Stages
While we sleep, we go through different sleep stages. Generally, two main stages are identified: REM and non-REM sleep.
REM sleep: rapid eye movement (REM) phase usually occurs around 90 minutes after falling asleep. It has such a name because during this stage the eyes rapidly move from one side to another behind closed eyelids. The REM phase is characterized by intense dreaming, which leads to a faster heartbeat and breathing. There is also hyperactivity of the amygdala, a brain area deputed to process emotions, which plays a central role during dreaming. Usually, adults should spend about 20-25% of their sleeping time in the REM phase. It has been shown that REM sleep is particularly important for memory and cognition. During this phase our brain performs memory consolidation, discarding excessive information and storing in the long-term memory everything else that is considered important (5,6).
Non-REM sleep: rest of the sleep is spent in the non-REM stage, which can be further divided into 3 phases:
Light sleep (or stage 1): it occurs at the beginning of the process when we are falling asleep and we are still switching between sleep and awakeness. Heartbeat and breathing start slowing down and muscles relax.
Core sleep (or stage 2): this is the major sleep phase, where we spend the majority of our sleeping process. The body temperature is kept low, and heartbeat and breathing are stably slow.
Deep sleep (or stage 3): in this phase, it is very difficult to be woken up, even by external disturbance. Deep sleep usually occurs in the first half of the night and it does not last more than around 90 minutes in total. Brain electrical activity, heartbeat, and breathing are at their lowest during this stage. The body will also use this time to repair itself, especially in case of recovery from injuries (7).
REM and deep sleep together account for the so-called restorative sleep. For good quality sleep, both stages should account together for a total of ~33% of the total sleep time. The aforementioned sleep stages can repeat more than once over the night, depending also on the total sleep duration.
Tips For High-Quality Sleep
Coming to the end of the article, it is very clear how fundamental sleep is and how it requires as much attention as our diet. As you want to make sure to eat high-quality food, you must also aim to achieve good quality sleep, at least for ~80% of your nights.
If you sleep too little or your sleep quality is too low for the majority of the nights, you will have a higher risk to develop a multitude of diseases, in particular neurodegenerative and cardiovascular diseases. You will also increase your chances of developing cancer, psychiatric disorders, and gaining body fat.
Here are a few tips for having great sleep:
First and foremost, if you are aged 18-60, you must aim for at least 7 hours of solid sleep per night. This is absolutely the bare minimum, with 8 and 9 hours being even more optimal. If you are above 60, you might be fine with even around 5-6 hours per night. It is interesting to notice that a small portion of the world’s population carries mutations in one or more genes that allow them to feel completely rested with as little as ~6 hours of sleep per night, even as young adults (8).
Stick to a regular sleep schedule. Your circadian rhythm is such a tightly regulated process that if you do not have a consistent sleep schedule you will end up unbalancing it.
Do not consume stimulants, such as caffeine, up to ~10 hours before bedtime. That is the amount of time that your body requires to clear up caffeine, the most widely consumed stimulant.
Stop eating 2-3 hours before bedtime. In particular, avoid heavy meals and foods containing spices as your last meal for the day.
Avoid blue light exposure close to bedtime. Ideally, you do not want to look at your computer, TV, or mobile for ~1 hour before sleeping. However, for some people, this is challenging, so a turnaround would be to use blue light filters for your screen or blue light-blocking glasses.
Keep a favorable room temperature. As our body temperature naturally drops when we are ready to sleep, being in a too-cold or too-warm environment will surely disrupt your sleep. Aim for a room temperature between 16 and 20 Celsius (~60-68 Fahrenheit). Sleeping naked also helps your body to more effectively cool down, especially when the environment is too warm.
Avoid working out or performing any strenuous exercise too close to bedtime. Instead, work out during the rest of the day, as physical activity helps in improving sleep quality.
If you have a smartwatch that is capable of tracking your sleep, either directly or through third-party apps, make use of it. Sometimes we overestimate the amount of time we sleep or we do not have a real perception of the quality of our sleep. Smartwatches can give you detailed information also on how much time you spent in each sleep stage, so you can see how these parameters improve or worsen accordingly to some changes you make in your sleep routine.
Naturally, a large variety of natural and synthetic supplements are available on the market for helping people with sleep-related problems. You can expect many articles coming up on this topic, which is extremely broad, and I have quite a strong opinion on it. So stay tuned and subscribe to not miss any future posts!
Take care, and sleep well.