Why do we need sleep? It’s an age-old question that researchers have puzzled over for generations. Short answer? No one knows. Long answer? There are several theories, each of which may explain it on its own or combined to give us insight into exactly why we not only need it but that we even do it.
It’s kind of crazy that after all these years, we still don’t fully understand why we shut down at night. Sure, we have all these cool things our bodies do while we snooze — produce melatonin, rejuvenate different enzymes and proteins, burn calories, revitalize metabolism, etc. — but somehow, there’s just no clear line of reasoning as to how we even started doing it let alone why.
There must be a scientific/anatomical reason for it, right? After all, research shows our bodies regulate sleep in the same way it does eating, drinking, and breathing. Those three things alone literally keep us alive and because we process slumber in the same way as those life-giving activities, it would appear sleep fulfills the same critical need for our overall health and well-being.
The mystery of slumber vs. the reality of life-giving processes
One reason understanding the “why” of sleep is difficult — especially when you recognize it affects our bodies the same way as the other three — is because the effectiveness of the act itself doesn’t rely on introducing any external matter or stimulus into our bodies to support or detract from our well-being. The other three are all about what goes in and what comes out, and if deprived of any of them — if we do not ingest food, water, or air — we die.
Putting food into our bodies gives us the energy needed to keep breathing and functioning properly. Eating provides the nutrients vital for keeping our limbs and muscles moving, our entire anatomy warm, and helps grow and repair tissue. A healthy diet with a good combination of protein, fiber, healthy fats, and carbohydrates supports brain and gut health, and muscle mass. While never recommended, a person can survive without food for up to 2-3 months if they have water.
Staying hydrated is even more important than eating — although no one should ever go without doing either for any length of time. We need to drink water to lubricate our joints, regulate our body temperature, protect our spinal cords and other sensitive organs, and eliminate waste and toxins through urination, perspiration, and bowel movements. The longest your body can survive without water is between 3-5 days, because by day 3, your organs are starting to shut down and if you don’t get water by then, it is most likely too late.
As far as breathing, well… That above all else is vital to our very existence. We breathe because first, as a living organism, we need to take in oxygen to survive and provide our body with the energy to function. Second, those processes of eating, drinking, moving, and even thinking produce waste gas known as carbon dioxide, and breathing it out releases it from our system. Our brains get signals telling it how much oxygen and carbon dioxide is in our blood and body, so it regulates our breathing to accommodate the in and out required to operate properly. After 4 minutes of not breathing, permanent brain damage can set in, and death happens usually if someone hasn’t breathed for 8 to 10 minutes.
You may be asking yourself, “What the eff does all this have to do with sleep?” Well, did you know that after just 24 hours without sleep, it affects your body, mind, and overall emotional state? While there are no true cases of someone literally dying from sleep deprivation — with that being the actual diagnosis — being deprived of sleep for any length of time leads to deterioration of various bodily functions that if continued unchecked can ultimately lead to death. There’s an actual form of insomnia known as fatal familial insomnia (FFI) that is very rare, starts out as mild and worsens over time, can lead to the inability to sleep for seven to 36 months — months not hours — and subsequent death. There is no cure for FFI, which is also hereditary, and the breakdown of the body due to lack of sleep is catastrophic.
All this is to say healthy slumber is considered as valuable as those other functions. After all, when you sleep, all this cool stuff happens, right? Your body rejuvenates, certain chemicals and minerals revitalize, cells reboot and so on. After a good night’s sleep, you feel refreshed and energized, and if you don’t get enough sleep, you are toast.
BUT… the true answer of “Why do we need sleep?” continues to elude and there are only theories. And because we like giving you insights into sleep whenever possible, we’d like to share five of those with you: Inactivity Theory, Energy Conservation Theory, Restorative Theory, The Clean-Up Theory, and Information Consolidation Theory.
INACTIVITY THEORY (aka Adaptive or Evolutionary Theory)
Inactivity Theory is also known as Adaptive or Evolutionary Theory. The whole idea here is that when humans were becoming, well, human way back when, being inactive at night was a survival function. Staying still and quiet during the most vulnerable times of day gave animals resting at night an advantage over others who were more active. Those keeping a low-profile in the dark wouldn’t have accidents, would not be killed by predators, and be protected. Thanks to natural selection, humans then evolved what was a behavioral and survival strategy into what is now considered “sleep.” Cool, right? Except there is a counterargument for this theory that it’s safer to stay alert even if it’s at night or in the dark to protect yourself. And, of course, there’s the counter-COUNTER-argument, that our fight-or-flight instinct kicks in when we’re asleep, too. It’s why we go through stages of sleep rather than a continuous REM, dead-to-the-world sort of process.
ENERGY CONSERVATION THEORY
Energy Conservation Theory is related to the Inactivity Theory in a way. It posits the simple idea that the primary function of sleep is to help you conserve your energy. This purpose for rest evolved when we were hunter/gatherers, helping us reduce our energy needs during those times when we weren’t using it to forage food for our tribe — when we were most inactive. Proof of this is that energy metabolism reduces as much as 10 percent in humans when we’re snoozing, and that our body temperature and need for calories decreases.
The Restorative Theory has a lot of supporters. The whole idea here is that sleeping restores what your body has lost while awake. When you go to bed for the night, the act of sleeping allows the body to rejuvenate and repair itself. This gained a lot of agreement when studies showed animals who are completely deprived of sleep lose all immune function and end up dying within just a matter of weeks. This may seem to counter the whole “there are no true cases of someone literally dying from sleep deprivation” but it does highlight the realization that “being deprived of sleep for any length of time leads to deterioration of various bodily functions that if continued unchecked can ultimately lead to death.” During our nightly rest, there are major restorative functions happening such as muscle growth, tissue repair, protein synthesis, and releasing of growth hormones into our system. Some restorative functions don’t just happen mostly while we sleep, but only when we sleep.
A case for this theory is also being made for its ability to rejuvenate the brain and cognitive function. See, when we’re awake, our brain’s neurons produce something called “adenosine” — a by-product of our cells’ activities. The build-up of this by-product is believed to be one of the reasons we perceive sleepiness. A little FYI: caffeine blocks adenosine’s effects on the brain and that’s why it makes us feel “awake”. Researchers theorize that the build-up of adenosine promotes the “drive to sleep.” It keeps accumulating during our waking periods and when we slumber, the body clears it out of our system, which results in our then feeling more alert when we’re awake. It’s a cycle.
THE CLEAN-UP THEORY
The Clean-Up Theory plays off the whole adenosine situation rather nicely. Here it is the belief that sleep allows the brain to clean itself up. Studies show that toxins and waste produced in the brain during the day are flushed out while we snooze. See, our brain cells produce waste products during our normal daytime activities and when we rest for the night, the flow of fluid through that thing in our skull increases, acting like a sort of waste disposal system. Basically, this theory is all about sleep flushing away the crap in our head.
INFORMATION CONSOLIDATION THEORY
Our final supposition is Information Consolidation Theory. Researchers who support this idea suggest we sleep to process the information we’ve acquired during the day and to prepare for the day to follow. Our rest locks things we've learned into long-term memory and this thought is supported by several sleep deprivation studies showing a lack of sleep seriously impacting our ability to recall and remember information. It’s like saying our brain is a storage facility and sleep is not only the key to our lockers but is also the movers loading in the boxes and furniture.
Sleep: Not one size fits all
The reason we need sleep and why we do sleep can be a combination of some or all these theories. End of the day? The quality of your rest affects your body, mind, and emotional well-being on a variety of levels. If you are struggling with your slumber at all, please seek professional help. Lack of it is no laughing matter and doing all you can to get the best snooze possible makes for a healthier sleep, dream, and waking life, overall.