why is sleep important for health

Why Is Sleep Important for Health, Longevity, and Performance

The three main components we can optimize for health and performance are sleep, exercise, and nutrition. While all three are very important, if you deprive one of each for 24 hours, it’s most likely that sleep deprivation will make you a zombie the fastest.

But why is sleep important for health? From the aspect of health, well-being, and recovery to improving brain performance, mood, and longevity, we will cover it all. It’s also important to see what happens in the body on a physiological level that affects these changes in the body.

What is Sleep?

Sleep is a natural biological process of regeneration. During sleep, thousands of little processes occur in the body at a physiological level, crucial for sustaining life. From muscle repair and cellular restoration to neural reorganization and flushing out of toxins, sleep promotes numerous benefits – sleep is the king of all.

A more scientific answer would be sleep as an active state of unconsciousness. It’s during sleep that the deepest brain restoration happens. The brain activity significantly lowers and the body is in a rest, digest, and repair mode. (1)

Why Is Sleep Important for Health and Well-Being

Besides the thousands of studies that show a deprivation of sleep can lead to numerous metabolic and neurodegenerative diseases, it’s known that sleep is essential for supporting every physiological process.

Sleep is when your muscles grow, your brain gets a deep clean, and your hunger and sex hormones are balanced. It’s what allows you to be a better, fresher, and more alert human the next day – potentially less of a zombie.

There are four theories of how and why sleep works (1)

  • Energy conservation theory – sleep reduces and conserves human energy.
  • Restorative theory – sleep supports the repair of cellular components.
  • Brain plasticity theory is concerned with consolidating memory, flushing out brain toxins, and neural reorganization.
  • Inactivity theory – is based on the evolutionary concept that inactive creatures are less likely to die (get eaten) in the dark.

Any physiological stressor causes oxidative damage in the body. Digestion of food, lifting weights, learning new information, and even just being alive. To function optimally, get stronger, better, and smarter, we need cellular repair. During sleep, that’s exactly what occurs along with many other effects supporting our physiological adaptations.

Phases of Sleep

Sleep is separated into two main categories, Non-RRM sleep, and REM sleep. Each one offers specific effects and benefits for the body. Once sleep cycle lasts from 90 to 120 minutes. Optimally, we get around 4 to 5 cycles a night. (2)

  • Non-REM 1
  • Light Sleep NR 2
  • Deep Sleep NR 3
  • REM Sleep

Non-REM 1 phase is when you transition from wakefulness to sleep. The brain is in the alpha brain wave band known as wakeful relaxation. It lasts for 1-7 minutes, it’s the drifting-off phase that’s easily distractable.

Non-REM 2 is light sleep as well, characterized by even slower (and mixed) brain activity. It lasts for 10-25 minutes, 50% of total sleep.

Non-REM 3 phase is the deepest, most regenerative sleep. It’s a slow wave sleep lasting from 20-40 minutes.

REM sleep is the 4th phase characterized by vivid dreaming and mixed brain activity shifting from alpha to theta waves.

Non-REM phases 1 and 2 are known as light sleep. NREM 3 is the deepest restorative sleep and REM is the vivid dreaming one.

Fun Fact

The ratio between Non-REM 3 and REM sleep changes during the night. The first few hours, we get an extended window of Non-REM sleep. As we go along the last few hours of our sleep, close to the morning, we increase the amount of REM sleep.

What Happens In The Body During Sleep?

The body has an internal clock called a circadian rhythm, which signals when we should go to sleep. Once lights are off, darkness causes the release of melatonin, an important sleep hormone that helps us fall and stay asleep.

Falling asleep is characterized by a slower heart rate and blood pressure. However, during REM sleep, if we have vivid dreams, K complexes, heart rate, and brain activity increase.

As we transition from NREM 1 to NREM 2 – brain activity changes. K-complexes and sleep spindles occur, which are bursts of neural (oscillatory) activity that help consolidate memory. (3)

The reason the NREM 3 sleep phase is the most regenerative is due to the secretion of growth hormone. (3) It is the main hormone that helps repair and regenerate tissues, restores metabolic energy, and is responsible for slowing down aging.

As we enter REM sleep, our physical bodies are partially paralyzed and only our eyes can move. Quite logical since REM stands for rapid eye movement, isn’t it?

Our respiration, ventilation, and respiratory flow are faster and more erratic during the dream phase. However, due to reduced muscle tone, we require less oxygen, so hypoventilation may take place. (3)


Brain activity and physiological processes change during each phase of sleep. Light sleep lowers blood pressure, heart rate, and respiration while transitioning to REM sleep can increase all of them during a vivid dream.

Sleep on health

Sleep for Health

Health is quite a large and complex subject, so to make matters simpler, we’ll discuss how sleep affects cardiometabolic factors, physiological functions, disease prevention, inflammation, and energy.

There is no shortage of studies showing how low-quality sleep or sleep deprivation leads to higher inflammation, neurological and cardiovascular diseases. It even impairs our ability to process glucose, increasing the odds of insulin resistance, diabetes, and obesity. (4) (5)

Sleep Deficiency and Deprivation

Sleep deficiency even impairs our ability to learn, focus, and memorize things. It causes emotional imbalances, making us angry, impulsive, and more depressed. This happens when our mood hormones are out of whack. (6)

Sleep deprivation may lead to dysregulation of the hypothalamic-pituitary axis – an important pathway for controlling metabolism, sleep cycle, immunity, and nervous system. This can lead to increased sympathetic nervous system activity and inflammation. (7) (8)

And if all that can be restored with getting good quality sleep, it sounds like a good deal to me. The ROI, or return on investment from sleep seems pretty good if you ask me. I mean, better heart health, brain performance, and more energy? All that for free?

While these metabolic markers like cholesterol and inflammatory factors can say a lot about our health, subjectively, it really matters how we feel. Higher energy, greater mood, and higher libido translate to better health.

As posted at Harvard Health – sleep enhances your ability to generate more ATP – meaning you’d end up with higher energy levels. (9) Also, lowering sleep debt may help you increase libido and reduce stress, improving the ratio of Cortisol to Testosterone which is of significant importance for athletes. (10)


Sleep is important for health as it supports numerous physiological functions. It helps us create more energy, restore neural connections, remove toxins and junk cells, balance hormones, and repair tissue. It’s the ultimate, natural, cost-free health supporter

Sleep and Longevity

How do you extend your lifespan? Well, what shortens it? Disease. Well, it seems quite logical that improving health and supporting one’s physiological functions leads to a longer life. But, don’t take my word for it, let’s see some data.

Sleep, Mortality & Longevity

Population-based studies and large meta-analyses show that sleeping too much or too little is detrimental to health. Those sleeping <7 or >9 hours had an increased rate of mortality. (11) (12)

Quality sleep is associated with longevity. It’s the ability of sleep to repair and turn on “longevity genes” or pathways that stimulate DNA repair. This is important because higher DNA damage accelerates aging. (13) (14)

Sleep on Human Growth Hormone

Growth hormone (HGH) is the ultimate anti-aging hormone, also known as the fountain of youth. But more isn’t necessarily better as each organism needs a balance between catabolism and anabolism, to sustain life. However, in many, especially the aging population HGH is too low, which results in degradation.

Sleep is important for this, as the highest amount of HGH is released throughout deep sleep. Studies show the III and IV phases of slow wave sleep, somewhere in the NREM 3 (which we said is most regenerative) is where the HGH magic happens. (15)

Sleep on Neuroplasticity

Brain longevity is about keeping the brain adaptable, plastic and functional. It’s during sleep that functional changes and neural reorganization occurs – enhancing neuroplasticity, or the brain’s adaptability. (16)

Sleep helps repair the brain, flush out toxic compounds and give your brain a deep clean.
It’s during sleep that the glymphatic system clears out plaque (beta-amyloid) which is known to aid in neurodegenerative diseases like Alzheimer’s when accumulated. (17) (18)


Quality sleep is associated with longevity, as it helps repair DNA damage and turn on “longevity genes”. It supports neuroplasticity, helps remove plaque in the brain, and consolidates memories. It’s during deep sleep that the most regenerative hormone, HGH is released.

Sleep and Performance

Numerous studies show sleep deprivation impairs the ability to lose weight. It can increase stress hormones, reduce insulin sensitivity and impair glycemic control. Plus, by throwing your hunger hormones out of whack, ghrelin increases making you hungrier than usual. (19) (20)

Exercise Performance & Recovery

What does that mean for sports performance? Without the ability efficiently transport glucose to tissues our energy-generation processes are impaired. That’s how sleep may help you be more energetic, and even improve stamina. Let’s look at some research.

Sleep is essential for cellular and systemic functions:

  • poor sleep may cause an increase in cortisol (in humans) and corticosterone (in rats) (21)
  • during sleep deprivation (catabolism) testosterone and IGF-1 are decreased, and protein synthesis is likely impaired (21)
  • in rats sleep loss causes metabolic abnormalities and cellular damage (22)
  • sleep plays an important role in recovery after training, and may likely reduce the risk of injury in athletes (23)
  • higher quality and duration of sleep are associated with improved performance and competitive success (24)

If that wasn’t enough, during sleep is when lactic acid, creatine kinase, and all these nasty by-products that come after muscle damage (exercising) are flushed out.

Sleep and Cognition

Do you remember a time you had poor, or distracted sleep? You woke up like a zombie right? Nothing’s funny enough, everyone’s bad, and everything’s against you, I mean the world is just a mess? Well, chill it off. You probably just need a good night’s sleep.

Sleep plays an important part in balancing neurotransmitters that help us feel happy, motivated, and satisfied. Yap. Depriving people of sleep may reduce dopamine receptor availability, (25) plus sleep is associated with depression. (26) We don’t want that, do we?

Regarding cognitive performance, sleep is essential for learning and memorizing.

  • It helps consolidate memories, especially during NREM 2 sleep where K-complexes and sleep spindles occur (27)
  • It restores brain energy and helps create more ATP, as depriving people of sleep increases Adenosine availability. (28)
  • Helps clean up plaque and toxic by-products in the brain, replenishing its energy (29)
  • Improves memory recall and working memory, plus it helps reorganize neural structures and recharge the brain (30)

I mean, what other component have you seen so influential? Sooner or later you’ll fall asleep, but optimizing it is a promising way to step up your cognitive performance and support brain health.


Quality sleep is essential for cellular repair, recovery, and regeneration, thus improving athletic performance. In terms of cognition, it’s essential for memorizing, learning, and processing information.

Quality vs. Duration of Sleep

When optimizing sleep, biohackers tend to focus on a specific part of sleep. But technicalities, theory, and nature are slightly different. While listening to a Matthew Walker podcast, I’ve realized it’s important to focus on sleep in general, not just NREM 3 phase, which is known to be the most regenerative.

Each and every phase has a specific reason. Some work for memory, some to clean up toxins, others to secrete HGH and accelerate recovery, etc. That being said, what’s the difference between duration and quality of sleep?

You can sleep (or be in bed) for 10 hours. But if that’s with lights on, in a noisy and distracting environment, especially at hot room temperatures, that sleep is quite poor. Compare that to 6 hours of quality deep sleep in a no-noise, blacked-out dark, and cold environment – you might be getting the same benefits.

So the idea is to get the recommended 8-9 hours in bed, optimally 8 hours of high-quality sleep to regenerate and restore the body. The point is to not just be concerned with time, but optimize your sleep environment for extra benefits.

Tips to Improve Sleep

How to optimize your sleep environment is a topic on its own, but very quickly, here are a few tips to help you sleep better and deeper, potentially extracting more benefits from sleep:

  • Sleep schedule: keep a consistent sleeping schedule (pattern) optimally every day.
  • Temperature: sleep in a cool environment, preferably with a blanket.
  • Light: Sleep in an absolutely dark, blacked-out room. Maybe invest in black-out curtains.
  • Blue Light: block blue light 3-5 hours prior to sleep by putting on blue-blocking glasses if you look at electronic devices.
  • Noise: absolutely cut all noise from traffic or devices around.
  • Radiation: turn off any internet, Wi-fi, Bluetooth, or light-emitting devices – consider putting your phone on airplane mode.
  • Eating: avoid eating heavy meals 3-4 hours before bedtime.
  • Wake-up: make sure you go out in nature, exposed to sunlight in the morning to signal wakefulness and alertness to your brain.
  • Breathing: slow deep and diaphragmatic breathing can help activate parasympathetic NS, helping you relax and fall asleep.
  • Caffeine: Avoid caffeine after 2-3 PM as it can disrupt sleep if it stays in your system.
Fun Fact

Following all these sleep-optimizing tips may result in a drastic improvement in your sleeping time, and quality. You’d be surprised to hear that many people who measure their sleeping with an Oura ring or Whoop 4 device get a boost of 30-50% REM and Non-REM deep sleep just by cutting blue light out.


Sleep is an essential biological process that supports health and vitality. It’s essential to regenerate the body, aiding in sports performance through muscle recovery. It’s crucial to brain health as it helps consolidate memories, restore energy and attention, and flush out plaque from the brain. It keeps our hormones in balance, supports immune system function, and helps us adapt. Poor sleep quality or sleep deprivation, on the other hand, is associated with numerous health issues, poor cognitive performance, and a shorter lifespan.


What happens if I don’t get enough sleep?

Sleep deprivation leads to fatigue, poor mood, lower focus, and productivity, as well as irritability and mood swings. Accumulated over time, it can detrimentally affect one’s metabolic and cardiovascular health.

What are the different stages of sleep?

Broadly, we can split sleep into Non-REM and REM phases. There are 3 NREM phases and 1 REM, in which we dream. Each stage performs a different task, such as memory consolidation or energy restoration, and is distinguished by particular brain wave patterns and bodily changes.

How many hours of sleep do I need each night?

The average recommendation is 8 hours of sleep a night for adults. This varies between people and ages, but somewhere around the optimal for adults is around 7-9 hours a night. Children need more sleep, while older adults usually sleep less.

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