As far as essential biological functions go, sleep is one of the most crucial- and unfortunately, one of the most overlooked. Sleep is just as critical a function as breathing, and, like breathing, it is a function most people don't spend time thinking about. When you do something repetitively, day after day, with some regularity in regards to schedule, you don't really stop and think about it. Sleep, however, is unique from something like breathing or blinking- it's a biological function that's in a class of its very own. It works in a much more nuanced way, and both the process and its effects require understanding.
When we look at all the things that have changed with evolution, sleep remains the single non-automated aspect of human life that we conserved in its entirety. Every other aspect of human life, from the way we eat to our form of shelter to the way we interact with each other, has changed drastically, but sleep has been the constant. For as long as humanity has existed, our system has needed a period of restful recuperation to function properly.
The phenomenon of sleep is ubiquitous across the animal kingdom. Some animals indeed have incredibly unique sleep cycles; certain species of birds can go months without sleep, while some animals such as dolphins can go to sleep with only one side of their brain, alternating between the sides to rest one half while the other stays fully awake. However, sleep cannot be avoided entirely in the animal kingdom.
Scientists have made significant progress in understanding the effects and necessity of sleep, but in many aspects, it remains a mystery. Why does the body require such a long period of slumber to rebuild? Why does this period vary so greatly from animal to animal? What causes dreams, and what is their purpose? There's a great deal we still have to learn about the multiple facets of sleep, but one thing is clear: sleep is both critical to every aspect of our well being and often neglected- especially in the modern world.
The science behind sleep lies in something called the circadian rhythm. The circadian rhythm is a natural process present in everything from animals to fungi to plants. This process is essentially a daily cycle that itself regulates the sleep-wake cycle (or its respective equivalent in plants and fungi) and is driven at its core by things like temperature and light.
The circadian rhythm process causes many physical, mental, hormonal, and emotional changes throughout the day. Sleep, in particular, is an example of the light-related circadian rhythm. Other examples of the circadian rhythm include fluctuations in body temperature and hormone levels throughout the day. In humans, the circadian rhythm is controlled and synchronized by something called a biological clock.
Our biological clock is what controls the circadian rhythm. This biological clock is an internal tool that manages every aspect of the circadian rhythm. For example, it is the internal biological clock that produces sleep hormones that "tell us" when it's time to sleep, helping control that aspect of the circadian rhythm. Many people with stable sleeping schedules often find themselves waking up at the same time every day with no need for an alarm clock- this too is because of their biological clock.
Biological clocks can change based on location, light, and change in environment. Whenever you take a flight across several time zones, you may be jet lagged for a couple of days, but once your biological clock "resets", you, along with your circadian rhythm, adapt to that environment. Likewise, people living in the far north or far south, where daylight can vary extremely based on the season, have biological clocks that have adapted to this.
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Though we may not realize it, sleep is actually a very active time for our organisms. While we lay there dreaming, with virtually no sensory activity, our system is doing a variety of different things. These things have to do with both our physical and mental health and are critical for our health.
Sleep is a time when the body releases many hormones. These hormones are countless; in children, for example, growth hormones are among the many that the body releases during sleep. In adults, hormones linked to reproductive health are secreted. Other hormones that the body produces during sleep can affect things such as weight and appetite; ample evidence suggests that lack of sufficient sleep plays a considerable role in being overweight.
In addition to the hormones that the body releases, sleep is a pivotal aspect for many different aspects of overall physical health and recuperation. The skeletal system requires adequate sleep for bone marrow health, which dramatically affects overall bone strength and blood cell production. Our immune systems also depend on rest in order to function correctly- not only does a good night's sleep help the immune system stave off illness, but most people's instinct to go to sleep when they're sick is grounded in biology; our bodies can recover much better when we're well-rested.
If you're somebody that likes working out, you probably already know a thing or two about nutrition and overall health. But it's not all about weights and diets- getting adequate sleep is crucial to see results. Obviously, not being fatigued helps with our performance during exercise, but a healthy sleeping schedule actively helps build muscle mass. Without enough sleep, your muscles don't get their glycogen replenishment, which is crucial for muscle mass. One study performed on individuals on the same exercise regimen and diet can have up to a 60% discrepancy in muscle mass when they don't get enough sleep.
These present only a fraction of the physical effects of sleep- its consequences are all-encompassing; if there is a bodily function your body performs, you can almost be sure that sleep affects it. But these consequences aren't just physical, as sleep also affects us on a mental level.
Everyone has felt the mental results of a poor night's rest. We simply cannot focus as well when we aren't fully rested or have to perform a task continuously for a prolonged period of time. But there's another reason that sleep is crucial for the mind- it helps us process, store, and consolidate all the information we've experienced throughout the day. It's during sleep that your mind organizes memories, getting rid of all the unnecessary information and adequately storing all relevant and helpful information.
Neglecting a proper sleep schedule on a long enough timeline has been proven to cause more severe and chronic mental disorders, including anxiety disorders, depression, and, in more extreme cases, even psychosis. Of course, some people have health issues that disrupt sleep, but many people are fully capable of having a proper sleep schedule and simply neglect to do so.
We can talk about hormones and bone marrow and glycogen all day, but what are the actual results of sleep (or lack thereof)? What do we stand to gain or lose from sleeping well or sleeping poorly? What are some tangible results in our performance?
Firstly, it's important to note that both getting too little and too much sleep are problematic. We'll touch on this in more detail a little bit later on, but it's important to understand this because both sleeping deprivation and oversleeping are two sides of the same coin, and bring with them their own respective set of issues. Therefore, when people discuss the effects of "unhealthy" sleeping habits, it's essential to distinguish the two main ways sleeping habits can be unhealthy.
Oversleeping is somewhat less of a concern, only due to it not being as prevalent as sleep deprivation and due to it having relatively fewer health effects than sleep deprivation. Nevertheless, it's nothing to sneeze at. One survey found that though oversleeping is linked to fewer issues than not sleeping enough, it was still tied to having a higher BMI and certain psychiatric problems.
On a day to day basis, oversleeping can cause people to feel lazy, sluggish, and irritable. People who sleep more will have more sleep inertia- which means the period of grogginess that comes after sleep (the period between sleep and full wakefulness) will last much longer. This is why neglecting sleep during the week only to "catch up on some sleep" during the weekend is doubly harmful- not only are you less productive during the week but sleeping in on the weekends will make you less inclined to get anything done at home on the weekend as well.
With that in mind, it's important to note that chronic oversleeping is usually due to underlying medical issues. If you're an otherwise healthy adult who regularly doesn't feel well-rested on 7-9 hours of sleep, it's definitely something to speak to a medical professional about. It's still a problem, but it's usually not an issue brought on by negligence or unhealthy decision making in the same way that not sleeping enough is.
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The bigger issue to address is not getting enough sleep. This is an epidemic that plagues most of the world; a Finnish report found that over 20% of their adult population does not get enough sleep, while that figure rises to about a third of the population in the United States, according to the CDC. Again, it's one thing to read about the chemical imbalances and hormonal issues that sleep deprivation can cause. Still, it's also essential to understand the results of it in layman's terms- how you feel, how you perform, how productive you are.
Insufficient sleep can be a result of different forms of unhealthy sleeping habits. Sometimes people have sleeping issues due to medical concerns, and, again, it's probably best to speak to a medical professional to resolve that. But negligent or irresponsible sleeping behaviors mainly happen in two ways: sleeping on a regular nightly schedule but not getting a sufficient amount of sleep each night or not sleeping for prolonged periods followed by a long period of oversleeping. Both tend to have the same adverse effects to varying degrees.
The first and probably most imminently noticeable effect of sleep deprivation is being temperamental or irritable in general. There's empirical evidence to support that an inadequate amount of sleep- even for one night- can cause irritability, anger, anxiety, and sadness in people. More importantly, the same evidence shows that people feel a substantial improvement in their mood once they begin getting enough sleep. Even without the ample evidence to support this, this is something we've all felt after not getting enough sleep. We find ourselves getting annoyed more easily and increasingly more irritable after a night of insufficient rest.
As you can imagine, these effects only get worse when we continue to neglect sleep day after day. And as stated previously, if someone neglects sleep for long enough, they are more prone to developing severe mental disorders related to anxiety, depression, and stress.
In addition to irritability and moodiness, sleep deprivation affects cognitive skills and our ability to perform and be productive. Cognitive skills across the board take a blow when we don't get enough sleep; anything from vigilance to reaction time to our ability to do simple addition has been shown to suffer when we don't get enough sleep. There's hardly an area related to cognition that doesn't suffer when we sacrifice sleep.
It's often an evil cycle that people get caught up in: sacrificing sleep due to work, work performance suffering from the lack of sleep, work piling up (along with stress), due to which sleep suffers. It's crucial to be aware of the fact that one often causes the other, and being aware of this is the first step to breaking out of this cycle in order to restore balance to our lives.
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Poor performance is obviously not desirable in any case; in both our professional and personal lives, we all want to be at the top of our game. But there are times when things can go from merely unfavorable to downright dangerous. The classic example of this is driving; we're always taught that it's better to pull over if we're sleepy, even just at the side of the road, and catch some shut-eye rather than continue driving fatigued. At the wheel, even falling asleep for one second can be the difference between life and death for the driver and all the other drivers or pedestrians around.
But this isn't limited to driving, and the consequences can be far more disastrous than a car accident. Human error can play a fatal role for dozens, hundreds, or even thousands of people in some lines of work, and the chance of human error increases exponentially as our cognitive abilities fall. Taking a quick look at some of the worst disasters out there, not many people know the role sleep deprivation has played in them.
The accident in the Prince William Sound, which resulted in 11 million gallons of oil spilling into the water off the coast of Alaska, had many culprits. Among them was sleep deprivation. When the captain handed over the reins to the third mate, the third mate was, according to the official investigation, sleep-deprived and had worked a very demanding day. Whether he was slow to react due to being sleep deprived or outright just fell asleep at the helm is unclear, but what is clear is that due to the sleep deprivation, he didn't react in time as the ship ran aground over Bligh Reef.
Two of the most famous nuclear power plant disasters in the world were also linked to insufficient sleep. Though not much more detail has been given in the reports of these accidents, other than "human error", many other authors and researchers have suspected this might be the case. Both of these accidents happened very late into the night/very early in the morning. It also isn't exactly a secret that workers in these power plants often had to work 12+ hour shifts.
Possibly one of the most memorable tragedies for every American is the Space Shuttle Challenger exploding only a minute after its takeoff. And though you'd be hard-pressed to find many people (American or not) who haven't heard of the disaster, not many people know the actual cause. The "human factors" attributed to the cause of the explosion were actually from "severe sleep deprivation"- something even NASA has stated openly. Workers at NASA were once known for voluntarily staying overnight and working on as little as 2 hours of sleep, night after night. And though NASA called this "admirable", it approached such practices with much more severity following the accident.
And these are just a few examples of many, many fatal accidents that have stemmed from workers getting insufficient sleep. It's a deadly practice common across all sorts of jobs- sometimes due to poor practices (such as in the case of Chernobyl or Three Mile Island) and occasionally due to overzealous, dedicated workers (such as in the case of NASA). But even if your job doesn't carry the implications of such jobs, sacrificing sleep for the sake of work is not a good habit- and you, along with your work, will suffer for it.
So we get the effects of sleeping too much or not sleeping enough- but how much sleep is just right? For this, it's essential to understand the types of sleep we get. There is non-rapid eye movement sleep (NREM sleep) and rapid eye movement sleep (REM sleep). Combined, these two distinct stages make up for an entire night's sleep. Throughout one night's sleep, stages of REM and NREM sleep alternate 4-6 separate times and last an average of 90 minutes. However, as the night turns into morning, the stages tend to get longer and longer.
The most important parts of these two stages are the deep sleep stage of NREM sleep and the REM sleep in its entirety. Deep sleep (otherwise known as slow-wave sleep) is when our bodies repair physically. REM sleep is responsible for our mood and energy. The most unimportant are the transition stages from NREM into REM sleep, but that is an unavoidable process known as light sleep. Basically, it's not the total amount of sleep you're getting; it's the quality of that sleep that you get that really matters.
Most adults need anywhere from about an hour to just under two hours of deep sleep a night total, throughout the various stages. They also need about 95 minutes to two hours of REM sleep total in one night. Light sleep is by far the longest part of anyone's sleep cycle, accounting for 4.5 to 5 hours of sleep every night as our bodies transition from NREM to REM sleep. And though it's considered the least vital in terms of function, scientists do still believe it's good for us. Therefore, the recommended amount of sleep for a healthy adult is 7-9 hours.
Some people may sleep 9 or more hours and still feel not rested, and that's because they aren't getting the deep sleep or REM sleep they require. There can be several medical issues linked to this, and, as stated previously, is best to bring up to a medical professional. Likewise, scientists did discover a gene that allows people to function properly on 6 hours of sleep- but that gene is estimated to be in just 3% of all people. So chances are you need at least 7 hours a night- and definitely no less than 6.
Sleep is misunderstood and incredibly underrated and continues to be neglected more and more for several reasons. This is for many reasons- overconfidence, overwork, and a general misunderstanding of the phenomenon. Many of these reasons are usually intertwined or part of the same evil cycle. As we continue addressing this issue to encourage people to fix their sleeping habits, please stay tuned for our next blog post where we'll discuss modern sleeping issues and trends related to sleep pertaining to today.
Other helpful links and resources:
How sleep heals the body?
How sleep affects mental health?
Need sleep? Whats in it for you?