Coffee down, eyes closed. Your body will thank you.
The Science and Benefits of Sleep
Don’t sleep.
Don’t sleep.
Don’t sleep.
Don’t sleep.
The words repeatedly echoing in my head at 3 AM just a few weeks ago as I chugged along in front of my computer, preparing for my upcoming finals. With over 200 pages of notes to study for an exam just a day later, sleep was my second biggest enemy that night (the first being the professor who gave us so many notes to begin with).
And thankfully, I didn’t sleep. Not until 4 AM at least, when I finally finished my notes, walked to my room, and just faceplanted into the bed.
This reality is one that many of us are all too familiar with. Whether it be college students studying for exams, parents watching their newborn child, a grumpy employee trying to finish their report due the next day, and so on. It seems that when it comes to our lives, sleep is on quite a low rung on the ladder of our priorities.
This is despite all of us knowing that we probably should be getting sleep. Doctors, parents, teachers, bosses, and almost everyone else is constantly telling us we need to sleep more.
But… why? What exactly does shutting your eyes for 8 hours at night help accomplish? Surely it’s okay to skip it every now and then, right?
In this article, I attempt to explain to you what is sleep is and how its controlled, the benefits of sleep, and how sleep is related to human longevity. And hopefully, it will convince you to skip that next episode of the show you love and get some well-deserved shut-eye.
So… what is sleep?
You close your eyes and melt into your bed. Next thing you know, the sun is shining through the windows into your eyes, waking you up the next day.
What exactly happened during the time skip? I mean we all know that macroscopically, you laid in the bed, shifting positions several times through the night, drooling with your mouth open, and in some cases, letting out snores loud enough to wake the neighbors.
But what exactly happened down at the physiological and maybe even the cellular level?
The Physiology of Sleep
Sleep is essentially controlled by very fine collaboration between a few major structures in the brain that you may have heard of before.
Within the hypothalamus of the brain is a group of neurons called the suprachiasmatic nucleus (SCN) which receives information from the eyes regarding the amount of light in your environment. This allows the body to finely control your sleep schedule to match it with the amount of light, forming the circadian rhythm or the sleep/wake cycle. The SCN communicates with other cells in the hypothalamus, which control the overall process of sleep. The hypothalamus releases a hormone called GABA which decreases the activity of arousal centers and essentially powers you down.
The brainstem works with the hypothalamus to control the transition between sleep and being awake. The brainstem works with the hypothalamus to also release GABA, and when one needs to wake up, these areas trigger the release of hormones like cortisol. The brainstem also releases signals that relax the muscles of our limbs so that we are able to dream without acting it out.
The pineal gland is a tiny, pea-shaped gland that releases a very important hormone when it comes to sleep: melatonin. Melatonin is produced in the pineal gland in response to darkness and production stops with exposure to light. The release of this hormone, then, is extremely important in the regulation of the circadian rhythm and triggers the cascade of events that leads to drowsiness & fatigue, and eventually sleep.
The basal forebrain and midbrain are involved in the release of another chemical called adenosine. This hormone builds up over the course of the day, slowly bringing about fatigue and sleepiness. Caffeine actually works by blocking the action of adenosine, thereby reducing fatigue and increasing alertness at least for a temporary period. However, once caffeine leaves your system, the build up of adenosine during the energy spike leads to what is commonly experienced as a massive post-coffee crash.
Phases of Sleep
You might think that sleep is just 8 hours of continuous lack of activity. But actually, there’s a lot of different phases of sleep with very different characteristics and very different levels of brain activity.
Firstly, there’s two main types of sleep: rapid eye movement (REM) and non-REM. Non-REM sleep is further subdivided into 3 phases, and over the course of the night, you go through REM and all three phases of non-REM sleep in a cycle tightly controlled by the structures I laid out earlier.
As you just start to drift off to sleep, you enter Stage I non-REM sleep, which lasts just a few minutes. During this phase, your heart rate, breathing rate, and eye movements slow down as your muscles relax. You may also occasionally twitch during this phase. Your brain waves also slow to reflect a transition to a calmer state with less activity than when awake.
Next, you enter Stage II non-REM sleep. This further slows the heart and breathing rates while stopping eye movements entirely and dropping your body temperature. This stage is the longest out of any other stage of sleep, lasting 25 minutes in the first cycle of sleep and getting longer with successive cycles over the night to overall represent 45% of total sleep.
Then you enter Stages III and IV of non-REM sleep, which are referred to as the deep sleep stages. During these stages, your blood pressure, heart rate, and breathing rate have been considerably lowered and your muscles fully relax, allowing you to rest. This stage of sleep is the one that helps you feel refreshed when you wake back up, and these stages are also the hardest to wake someone up from.
The last stage of sleep is rapid eye movement (REM) sleep, which, as the name implies, is marked by a rapid movement of the eyes under the eyelids. This stage first takes place roughly 90 minutes after falling asleep, and repeats every 90–120 minutes. Unlike the other phases of sleep, this stage is marked by a sudden increase in brain activity. It is thought that dreams occur during this stage, which is why the limbs become temporarily paralyzed during this stage to avoid acting your dreams out. In babies, REM sleep makes up a significant proportion of sleeping time, while in adults it represents about 1/4 of the sleep duration.
Why Do We Sleep?
So… we don’t exactly have an answer. Despite all the research that has gone into trying to elucidate the purpose of sleep, all we have are a host of different theories that fit together to give a rough answer.
For example, one theory suggests that sleep served as a way to keep organisms safe by preventing them from being active during the times that were most dangerous to them. For humans, with our lack of night vision, the darkness serves as a major source of danger and so our bodies adapted to keep us grounded and inactive during the night and thereby prevent us from blindly foraging the woods while predators more attuned to the darkness roamed freely. However, some people argue against this theory by suggesting that consciousness would be a far better defense mechanism in an emergency, even during the night, than sleep is. As such, sleep would have rapidly been deleted from our evolutionary history (or not appeared in the first place) if there wasn’t another crucial reason for it.
Another, more common, conjecture is that sleep simply exists to restore and repair. It allows our body to recover from any stressors (physical, mental, or emotional) that we may have encountered during the day. This has been supported by a lot of evidence that suggests that repair & growth pathways in the body are most active during sleep. Similarly, in the brain, various toxins and metabolic factors that may build up and lead to poorer cognition are eliminated during sleep, allowing a mental reset every night.
In addition to a restoration function, it is also thought that sleep allows a significant conservation of energy and resources, thereby allowing an individual to survive longer on the same amount of energy intake. While this is not necessarily a massive issue for a large portion of the world today, with the massive amounts of food available to us at our whims, it certainly would’ve been an issue back when sleep first evolved over 700 million years ago.
However, a very interesting new theory arises from studying brain activity in sleeping individuals. While we might expect a lack of activity in the brain during sleep, scientists noted a lot of activity related to both processes like dreaming as well as changes in the very structure and organization of the brain itself. This process is referred to as neuronal plasticity, where neurons (brain cells) break and form different connections with the neurons around them for a variety of still widely unknown functions. Such plasticity allows learning, memory, habit formation, physical coordination, and virtually every other process that the brain is heavily involved in. Without such plasticity, our cognition would never develop past that of a newborn. Interestingly, many scientists estimate that this is why infants sleep so much: they promote neuronal plasticity in order to adapt and grow into more intelligent and capable versions of themselves.
While all these theories exist, none of them are mutually exclusive. This means that both the inactivity theory and the plasticity theory may be true. Honestly, looking at all the data and the research that has been done thus far, and knowing the complexity of the process that is sleep, it would be juvenile to assert only one function onto it. It is a process so crucial to our existence that the answer to “why we sleep” may be no easier to answer than “why do we exist?”
Sleep and Longevity
Perhaps the most interesting sleep research coming out now is the work relating sleep patterns and styles to one’s longevity.
It has long been shown that sleep tends to become more irregular, dysregulated, and overall worse as we age. In a study by Mazzotti et al., they found the older individuals had a far lower sleep efficiency (total time asleep vs. total time in bed) and less REM sleep. This is largely the result of an aging and slowly degenerating suprachiasmatic nucleus (SCN), disrupting the circadian rhythm greatly.
Flipping the correlation on its head, research has also now shown that insufficient sleep can make our cells age far quicker, even if it’s just one night. Poor sleep has also been implicated in increased inflammation, which is a well known risk factor for many age-related chronic conditions and considered one of the driving forces behind the process of ageing itself. In an Alzheimer’s disease study, it was found that sleep problems, fatigue, use of sleep medication, trouble sleeping, and changes in sleep patterns are all associated with increased risk of Alzheimer’s disease, dementia, or death within four years.
Even sleeping too much has been associated with poor health quality and increased risk of death.
Poor sleep can also massively impact one’s mental health in the short-term. For example, lack of sleep has been shown to greatly increase the risk of depressive symptoms, which can lead to further physiological and behavioral complications associated with lower human longevity.
Some research into optimal sleep conditions for longevity found that strict adherence to sleep schedules was extremely crucial. So, unlike what so many people seem to believe, maintaining a regular time to sleep & wake is just as important as the number of hours we sleep every night. Interestingly, people with longer lifespans also seem to take short naps during the day.
Overall, sleep is an extremely well regulated process very directly tied to our health. Even one night of poor sleep can have very significant ramifications on our rate of aging as well as our short term health. So, next time you’re up at midnight binge-watching a show, hopefully you’ll remember this article and get some well-needed shut-eye instead.
