Why We Need Sleep: The Mystery, The Medical, And The Magic

Trying to find the answer to the age old question that asks “why we sleep?” is typically answered by reverse engineering the whole sleep process, and that means examining the effects on mammals when they are deprived of sleep. The results of sleep deprivation are well known and we’re all generally aware of the symptoms. Loss of brain function, disconnects from reality, utter exhaustion, and so on.

Many studies compare species and their responses to sleep deprivation to establish patterns that could reveal answers about sleep functions. By studying sleep dynamics with other species, we do get some data, but the big questions that reach to answer the mysteries of sleep and exactly why we require it are not scientifically proven.

Just because we don’t have a clear answer doesn’t mean that the vast amount of research on the subject has been a waste of time. Recently, a number of promising theories have begun to shed light on the subject, though the answers seem to suggest that multiple factors are involved. 

What we do know is that clear health benefits can be gained when we sleep a reasonable amount of time, and when we sleep uninterrupted so that our body can descend into REM sleep (rapid eye movement), and of course, owning the best mattress you can find is a consideration in this discussion as well. 

Sleep hygiene, such as scheduling sleep at a regular time, using tech like sleep machines, black out shades, masks, and other “Instrumentation” can drastically improve the caliber of your sleep.

Let’s take a look at the strongest theories that attempt to explain why humans require sleep, and why we simply can’t stay upright and awake 24 hours a day.

The Inactivity Theory

One of the earlier theories of sleep, often called the evolutionary theory, suggests that inactivity at night is an adaptation that served a necessary function by keeping organisms out of sight and hidden during times when they would be otherwise be particularly vulnerable. 

The theory suggests that animals that were able to remain silent and still during these periods of vulnerability had a clear advantage over animals that were active and became easy prey. These animals did not injure themselves in the darkness, for example, and were not hunted and eaten by predators. 

Natural selection refined this behavioral strategy, and evolved into what we know as sleep. Sleep itself is highly technically evolved, our brains being able to suspend our consciousness and even utilize automated systems that kick to breathe for us. 

An argument to this theory is that it is always safer to remain conscious during inactive times, even when lying still in the night, to be able to respond to predators that are active during this time. The ability to spontaneously awaken upon hearing even the most subtle noises does provide some advantage. Those “footsteps in the night” can suddenly awaken humans and put us on immediate high alert. 

Energy Conservation Theory

Not likely to be as much of a factor in societies where humans have ready access to food and water, one of the strongest components in natural selection is effective use of energy resources necessary for daily survival, and stretching those resources to the maximum.  This theory suggests that the primary purpose of sleep is to shut down systems that consume a lot of energy and 

Although it may be less apparent to people living in societies in which food sources are plentiful, one of the strongest factors in natural selection is competition for and effective utilization of energy resources. The energy conservation theory suggests that the primary function of sleep is to reduce energy consumption, allow metabolic systems to shunt energy used for digestion and processing of food. The most visible example of this in humans is napping after a big meal, or consuming our largest meal prior to bedtime, allowing our bodies to store energy resources.

Research has shown that energy metabolism is significantly reduced during sleep. Both body temperature and caloric demand decrease during sleep, as compared to wakefulness. Such evidence supports the proposition that one of the primary functions of sleep is to help organisms conserve their energy resources.

Restorative Theory

One hugely popular explanation for why humans require sleep is based on the long-held belief that sleep in some way serves to regenerate and refuel, replacing what is lost in the body while we are awake. Sleep provides an opportunity for the body to build cells, create hormones, remove toxins, and essentially reboot itself.

These ideas have recently gained a huge following based on evidence acquired from human and animal studies. Case in point: Animals deprived entirely of sleep lose all immune function, experience organ failure, and die in as quickly as weeks. This is further supported by findings that many of the high priority restorative functions in the body such as muscle growth, tissue repair, protein synthesis, mitochondrial repair and regeneration, and growth hormone release occur mostly, or in many cases only, during sleep.

Other rejuvenating elements of sleep occur in the brain and directly effect cognitive function. For example, while we are awake, neurons in the brain produce adenosine, a byproduct of, or exhaust fume if you will, of cellular metabolism. The accumulation of adenosine in the brain is thought to be one factor that leads to our perception of being tired. It’s the reason we need that Vente cup of coffee in the morning. 

To a neuron, caffeine looks like adenosine and binds to the adenosine receptor. Instead of slowing down because of adenosine, the nerve cells ramp up, rather quickly. Caffeine also causes the brain’s blood vessels to constrict, because it blocks adenosine’s ability to dilate them.

Scientists think that the gradual increase of adenosine during waking hours may promote the urge to sleep once concentrations are high enough in the blood.  As long as we are awake, adenosine gradually increases and remains high. It dulls our senses and creates fatigue. During sleep and at rest, the body has a chance to clear adenosine from the system, and, as a result, we feel more alert when we wake.

Brain Plasticity Theory

One of the most compelling explanations for why we sleep is based on research that suggests that sleep is correlated to changes in the structure and organization of the brain. This concept, known as brain plasticity, is not completely understood, but its relationship to sleep has several critical implications. It is evident for example, that sleep plays a critical role in brain development in infants and young children. 

Infants spend about 13 to 14 hours per day sleeping, and about half of that time is spent in deep REM sleep, the stage in which most dreams occur. Refinement and development of the cerebral cortex, and the degree to which brain plasticity will occur, is directly related to sleep in young and rapidly growing brains.

A link between sleep and brain plasticity is becoming clear in adults as well. This can clearly be observed by examining the effects that sleep and sleep deprivation have on people’s ability to learn and perform a variety of tasks.

This theory and the role of sleep in learning are covered in greater detail in Sleep, Learning, and Memory.

Because sleep is complex and esoteric, even delving into the realm of mysterious and intangible, science has made tremendous strides in discovering what happens during sleep and what mechanisms in the body control the phases of sleep and wakefulness. While this research may not answer the question, “Why do we sleep?” it does create new avenues to help generate new knowledge about this essential part of life, and for developing new treatments for sleep disorders.

We tend to think of sleep as a time when the mind and body turn off, and engage in a kind of suspended animation, which could not be further from the truth. The brain in fact, is fully awake, buzzing like a factory, driving and controlling all of the waste removal, metabolic processing, restoration, and regenerative activities that are happening- simultaneously.  Exactly how this happens and why our bodies are programmed for such a long period of slumber is still somewhat of a mystery. But scientists do understand some of sleep’s critical functions, and the reasons we need it for optimal health and well being.

One of the vital roles of sleep is to help us encapsulate and consolidate memories. Imagine how much data there is in a two dimensional video, and add sensory elements, physiologic processes, emotional processing, and other stimuli added to the The amount of information absorbed by a healthy brain is almost inconceivable.

As we go about our day, our brains take terabytes of information. Rather than being directly logged and recorded, however, these facts and experiences first need to be processed and stored; and many of these steps happen while we sleep. Overnight, bits and pieces of information are transferred from short-term memory strings to stronger, long term memory strings, imprinting them permanently into neuronal networks. 

Research has also clearly demonstrated that after people sleep, they tend to retain information and experience better results on memory based testing. The human body requires long periods of sleep to be able to restore and rejuvenate, to grow muscle, repair tissue, and synthesize hormones.

How Much Sleep Do We Really Need?

Healthy sleep is critical for everyone, since we all need to retain information and learn skills to be able to thrive. This is likely the reason that children, who acquire language, social, and motor skills at astonishing speed throughout their development need far more sleep than adults. While adults manage well on 7-9 hours of sleep per night, toddlers need roughly 11 to 14 hours, young children between 9 and 11 hours, and tweens and teenagers between 8 and 10 solid hours. 

During these critical periods of growth and development, younger people need restorative sleep that is uninterrupted and regularly scheduled, for optimal development and alertness.

Unfortunately, humans can’t just accumulate sleep deprivation and then log many hours of sleep to make up for it. The best sleep habits are consistent, healthy routines that allow all of us, regardless of our age, to meet our sleep needs every night, and keep on top of life’s challenges every day. Part of that process is a mattress that promotes restful, energizing sleep. You can check out our list of carefully curated mattress dealers here.