Sleep is essential – this much we know. As equally important as nutrition, hydration and exercise, consistent and quality sleep forms a cornerstone of healthy living. Remarkably, we spend roughly a third of our lives sleeping! Its absence swiftly leads to fatigue, irritability, decreased efficiency, increased errors, and, in severe cases, life-threatening issues. With something so crucial to our lives, it may come as a surprise to learn that much remains unknown 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? In fact, the impulse to sleep often surpasses the desire to eat. Sleep rejuvenates, allowing you to face the new day, and it improves your mood, health, and cognitive function. There are many scientific theories that explain why rest plays a vital role in our lives, and these theories add up to a credible overview of the functions sleep serves.

Theory #1: Sleep saves energy. Some scientists believe that sleep is a method of energy conservation. During waking hours, humans use a great deal of energy, and a significant component in natural selection is how well one can utilize their energy source, namely food. Perhaps one way we do this is through sleep. Sleep helps reduce energy consumption by lowering metabolism, body temperature, and the need for food. This state allows us to “recharge our batteries” and conserve our resources.

However, some dispute this theory, considering sleep’s unresponsive state seems counterintuitive in the context of natural selection and survival within a food chain. Is saving energy worth losing your life in the wild? Probably not, and yet rest remains a universal phenomenon. In today’s modern world, where food production is more plentiful[HE1] , the conservation of energy may be an underlying function of sleep that we’ve outgrown.

Theory #2: Sleep heals the body and refreshes the mind. As the day unfolds, its demands inevitably take their toll on all of us, and one popular theory is that the night serves as a period dedicated to repair and restoration. 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. During this time, our neurotransmitters and hormones are restored to normal levels, and wounds heal faster. Throughout the day, our brains produce adenosine, a byproduct of cell activity, which is thought to contribute to feelings of drowsiness. While sleeping, our brain can clean these from our system for improved cognitive function. Without sleep, our attention spans are reduced, and our short-term memory suffers as we stifle yawns.

Theory #3: Sleep helps aid memory processing and learning. Our five senses give us an extraordinary amount of information daily – an overwhelming amount 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 because no additional information comes in. This can better prepare us to take in and store more 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 environments.

Though none of these theories provide definitive answers, they do offer logical reasons for why sleep is an essential part of life.

How Much Sleep You Need?

Every person is different, but luckily we have some generally agreed-upon recommendations courtesy of the National Sleep Foundation:

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 recommendations 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 works for you and stick with it consistently – but be careful not to oversleep because that can carry its own health risks.

Do you depend on caffeine every day to stay energized? Do you struggle to stay asleep at night? It’s possible you’re not getting the quality sleep you need. Consider reassessing your sleep habits and environment to optimize your sleep time. Neglecting this can adversely affect your productivity, focus, and overall health.