It used to be thought that sleep was one of three pillars—along with a healthy diet and adequate exercise—needed for a long and healthy life, but recent advances in polysomnography (that is, the study of sleep) are forcing us to re-evaluate our attitudes. Sleep is no longer considered just one of three pillars. In fact, sleep is now thought to be so important that it’s more like the foundation under which the other two rest.
Shakespeare once referred to sleep as “Chief nourisher in life’s feast” and the science is rapidly accumulating to confirm this evaluation. Forget about pop culture’s misconceptions—sleep is nothing like being dead. Sleeping is a highly metabolic process that performs crucial functions that are absolutely essential to a healthy life. We've delved into the science of sleep, and why it's so important.
This funny thing called sleep
There are four stages of sleep and two “types” of sleep: NREM (non-rapid eye movement) and REM (rapid eye movement). The brain cycles through three different stages of NREM sleep—in which our bodies enter deeper and deeper states of sleep—until we eventually start dreaming. It’s during this dreaming state that our eyes start to dart about underneath their lids, a strange observation from which the REM type of sleep gets its name.
As we enter Stage 1 of NREM sleep—the lightest part of sleeping, just as we start to drift off—our brain waves seem to slow and smooth out. A sleep scientist monitoring your brain waves in the lab will then start to see little, fluttered, waves of activity as you drift off further, entering into Stage 2 of your NREM pattern. These are called “sleep spindles”. The brain seems to smooth out further as you enter Stage 3, until a remarkable thing happens.
You begin dreaming. Suddenly, your brain waves become ecstatic, reporting as though you were wide awake. Your body paralyses itself, leaving you unable to move, everywhere except your eyes, of course, which move about frantically. This strange nature of sleep—REM sleep—is not unlike something a psychopath would experience while awake, except it's a routine part of your everyday sleeping pattern.
Why you should sleep
As strange as sleep sounds, it’s not without purpose. In fact, sleep is so efficient that Mother Nature has, for billions of years of natural selection and evolution, saw fit to preserve it in every animal. There is not one creature known to science that doesn’t enter some stage that can’t be described as sleep, and for good reason.
When we enter NREM sleep, our brains begin the process of “sorting” our experiences, both from the previous day and from our entire lives. It’s a process a bit like a businessperson clearing the clutter from a desk, or a gardener pruning a rose. Our brains dispose with what’s not deemed to be necessary, and give those that are most important high priority. Then, during REM sleep, the brain takes this “sorted” information and integrates it into the brain—think again of the businessperson taking the most important documents from the desk clutter and filing them safely away.
It takes around eight hours to fully perfect this process of memory integration—eight hours which, funnily enough, is the recommended amount of sleep we should get every night. Sleep less than eight hours, and you dramatically cut off the amount of REM sleep you get. This is because NREM sleep tends to dominate the first four hours of our sleep cycle, with REM dominating the latter four hours. Sleep for just six hours one night, and you could lose up to ninety per cent of your REM—or in other words, your ability to form memories.
Sleeping to learn
Because sleep helps us to form and retain memories, it should perhaps come as no surprise that it also helps with learning. Our brains can only take in so much information in the short term, storing what it can in the hippocampus region. Think of the hippocampus as a memory stick, with limited storage. As we sleep, our brain transfers the information from the hippocampus to the cortex which, using the same analogy, can be considered a more permanent hard drive. If you ever find yourself revising for an exam or test, consider napping between sessions. Even twenty minutes of rest will free up space in the hippocampus for greater fact retention.
It’s important to know that the more sleep spindles a person experiences in NREM sleep, the more that person can learn both fact-based and motor-based skills. Most of these sleep spindles seem to occur in the later hours of our sleep cycle, sandwiched between our majority-REM stages. Skipping that full eight hours could mean the difference between passing or failing an exam, whether it be a SAT paper or a driving test.
The health benefits of a good night’s sleep
Studies have consistently demonstrated that getting your eight hours will not only make you feel happier, but can make you slimmer. This is because a lack of sleep disrupts how the body regulates hormones that control appetite and food satisfaction. Poor sleepers tend to crave unhealthier food, and consume an extra 300 calories a day, which over the years can amount to significant weight gain. Hit the gym on a day after a bad night’s sleep, and you’ll burn more muscle than fat. The REM stage of sleep also helps to construct creative and innovative ideas, giving a whole new basis to the old saying “let’s sleep on it” when trying to solve a problem.
The consequences of neglecting sleep
Sleeping for six hours or less can wipe away up to 70 per cent of our immune response. Consistently failing to sleep for more than six hours not only decimates the immune system over time, it hinders our ability to ward off flu and cancerous cells. Just one week of poor sleeping is enough to raise our blood sugar levels to that of a pre-diabetic. Even more disturbingly, not getting a full eight hours hampers our brain’s ability to clean up and flush out certain toxins that accumulate around the hippocampus and other regions—which can lead to dementia in later life.
The most shocking fact may be this: the brain starts to fail after 16 hours of being awake. If you get behind the wheel of a car after 20 hours of not sleeping, the brain is impaired to the same degree as being legally drunk!
How much sleep do we really need?
At an absolute minimum we need seven hours, but eight or nine are perfect amounts. Given that the human “recycle rate” is 16 hours—that is, the brain requires a recharge after 16 hours of being “on”—we need to try and sleep around this 16-hour mark. Naps can be useful for “catch up” sleep, for an optimal time of around 90 minutes, as this allows for a sufficient amount of REM sleep to occur in healthy individuals.
It is important to remember that sleep opportunity is not the same as total sleeping time. If you give yourself an eight-hour window, say, between 11pm and 7am, you’re unlikely to sleep for eight hours because that includes the time it takes to drift off, plus any restlessness you might experience, including waking up in the night. Ideally, you should give yourself a longer sleeping opportunity for a greater sleeping time.
There are no detrimental effects from sleeping too much, at least not that we know of. So bonne nuit! Good night! And remember, sleep is the feast of life. It’s not being lazy, or idle. It’s a crucial life function. Take a nap, because you’ve earned it—even if it means skipping the gym. It’s far more important.
If you're struggling to get your recommended hours each night, read our tips on how to get a better night's sleep.
This article was influenced by Matthew Walker’s phenomenal book ‘Why We Sleep: The New Science of Sleep and Dreams’ by Penguin Books. Buy it here at: Waterstones.