A man squeezing a pillow in bed.

Why Do We Need Sleep, And How Much?

Jun 26, 2017

Sleep is essential. That much we know. As important as food, hydration, and exercise, consistent and quality sleep is a pillar of a healthy life. We spend roughly a third of our lives doing it! Without it, we quickly grow tired and irritable, we become less efficient and more mistake-prone, our health suffers, and in some extreme cases, we might even die. So, it may come as a surprise to learn that something so crucial to our lives remains somewhat of a mystery to scientists. There is no single concrete answer to why we need sleep.

But from a practical perspective, why wouldn’t you want to sleep? It leaves you feeling refreshed and ready to take on the day ahead and improves your mood, health, and brain. Few would turn down a nap if offered one right now. In fact, the drive to sleep will ultimately even trump the desire to eat. However, there are many theories on the scientific explanation for sleep, and these theories add up to a credible overview of what functions most believe sleep serves.

It’s to conserve energy. Much like a battery, humans use a tremendous amount of energy throughout their waking hours, and a significant component in natural selection over time has been how well one can utilize their energy source, namely food. Some have speculated that one way we do this is through nighttime rest. Sleeping decreases our energy demand and usage, reducing metabolism, body temperature, and need for food. A restful state theoretically allows us to “recharge our batteries” and conserve our resources.

However, some dispute this considering that sleep’s unresponsive state would seemingly not bode well for any creature in a more natural food chain. Is saving some energy worth losing your life in the wild? Probably not, and yet sleep remains a universal phenomenon in life. And in most of today’s modern world, there’s more than enough food to go around, so this may just serve as an underlying function of sleep that we’ve simply outgrown for now.

It’s to heal the body and refresh the mind. The day inevitably takes its toll on all of us, so one popular theory posits that the night is there to repair. Sleep gives us a chance to stop, relax, and let our bodies and minds rebuild. Many restorative bodily functions, from muscle growth to tissue repair, occur mostly during non-REM sleep. Our chemicals and hormones restore to normal levels, and our wounds heal faster. And without sleep, experiments with animals have shown the shutdown of immune system processes and, ultimately, death. During REM sleep, our brain gets some love. While awake, our brains produce adenosine, a byproduct of all the cell activity, which is thought to contribute to feelings of drowsiness. While sleeping, our brain can clean these from our system and wake us back up. Without sleep, our attention spans are reduced, and our short-term memory suffers as we stifle yawns. This leads us to our final theory…

It’s to help aid memory processing and learning. With our five senses, we’re exposed to an extraordinary amount of information every day. An overwhelming amount, perhaps, if not for sleep. A day of new experiences and knowledge needs to be processed and stored as memories, while unimportant information and stimuli can be tucked away or thrown aside. New connections can be made more easily while we sleep as new information to analyze comes to a halt for the night. Sleep also better prepares us to take in and store that new information the following day. There’s a reason infants and young children spend so much time sleeping. Their brains are still forming and learning how to process their new environment.

Though none of these are technically “proven,” they do seem to point to logical solutions to why we spend so much of our lives checking out with our eyes closed. And one thing remains undisputed: Sleep is essential.

How Much Sleep You Need

We obviously need sleep, but how much? Luckily, we have some generally agreed-upon recommendations courtesy of the National Sleep Foundation:

Recommended Hours of Sleep

Newborn (0-3 months): 14-17 hours

Infant (4-11 months): 12-15 hours

Toddler (1-2): 11-14 hours

Preschool (3-5): 10-13 hours

School Age (6-13): 9-11 hours

Teenager (14-17): 8-10 hours

Adult (18-64): 7-9 hours

Older Adult (65+): 7-8 hours

Of course, these figures aren’t universal. Your specific sleep needs may differ, and that’s ok. If you’re questioning how much sleep you should get, consider what makes you feel rested. Is it 6 hours? Is it 10? Find what genuinely works for you and stick with it consistently. And be careful once you find it to not then oversleep, which carries its own risks and health concerns.

Do you suffer from health issues, or at risk for any? Do you rely on daily caffeine intake to keep you going? Do you struggle to stay asleep at night? It’s possible you’re not getting the sleep you need, and you may need to reassess your sleep habits and environment to optimize your nighttime hours. If not, you’ll quickly collect what’s known as sleep debt, or hours of optimal sleep missed, harming your productivity, your focus, and your health. Make your sleep schedule a priority.

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