The Most Comprehensive List of Sleep Facts

Article at a Glance: 

  • Humans are programmed to spend about 1/3 of their lives sleeping; it is just as important as nutrition and exercise because it helps regulate vital biological functions (like your circadian rhythms).
  • Modern lifestyles have changed dramatically since the days when our ancestors solely relied on sunlight and fire to illuminate the spaces around them. 
  • Sleep is essential for your memory, mood, processing information, and regulating hormones.
  • When you don’t get adequate sleep at night, you put yourself at greater risk for several health concerns, including weight gain, mood disorders, circadian rhythm disruption, diabetes, heart disease, cancer, and Alzheimer’s disease.

Sleep and Evolution

  1. Hunter-gatherer societies in history relied on sunlight exposure and temperature to help them schedule their daily activities — including when to wake up and when to fall asleep. The tribes would go to sleep shortly after dusk as the temperature started to drop, and they would wake up around sunrise when the temperature would increase again.
  2. We spend about ⅓ of our entire lives sleeping.
  3. Sleep is just as important as diet and exercise.
  4. At night, after the sun has gone down, the sensors in your eyes signal to your brain that it’s getting dark outside and that it’s time to start winding down to go to bed. This signaling helps the body naturally produce melatonin so that you can fall and stay asleep.
  5. It took over 3.6 million years for mother nature to create our need to 8 hours of sleep each night. And in the past 100 years alone, we’ve managed to lower that number by an average of 20% each night. (Matthew Walker)
  6. Exercising regularly helps promote consistent and healthy sleeping patterns; however, working out right before bed may make it more difficult for you to fall and stay asleep.
  7. “Sleep is the greatest legal performance-enhancing drug that most people are probably neglecting.” (Matthew Walker)
  8. During sleep, we produce a growth hormone that helps to repair damaged cells. When we sleep less, we have less of this growth hormone present to repair our cells. (Dr. Satchin Panda)


Benefits of Sleep

  1. Getting a good night’s rest can help you improve your short term memory.
  2. Getting your beauty sleep can help regulate hormones that control appetite, so you’ll eat fewer calories overall when you snooze for seven to nine hours per night, compared to when you’re experiencing a sleep deficit. (National Sleep Foundation)
  3. During REM sleep, the brain takes old information and combines it with new information that we’ve learned that day. This helps us form new connections and associations. Because of this, it’s more likely that we might be able to find or create new solutions to previously unsolvable problems after we’ve had a good night’s sleep and a health information flow into the memory center of the brain.
  4. Sleep is crucial for strength training recovery because it helps repair muscle throughout the body after a strenuous workout. Conversely, inadequate sleep can interfere with the body’s ability to recover after lifting weights and inhibits the body’s ability to build maximum muscle strength. (

Sleep Deprivation

  1. Of all the creatures in the animal kingdom, humans are the only ones to deliberately deprive themselves of sleep, or delay it, for no reason.
  2. “Sleep deprivation weakens our immune system, making us more susceptible to garden-variety illnesses, like the common cold, and sets the stage for the development of more serious diseases. A lack of sleep also has a major impact on our ability to regulate our weight. In fact, a Mayo Clinic study found that sleep-deprived individuals ate an extra 559 calories a day than their well-rested counterparts.” (Arianna Huffington)
  3. Sleep deprivation has been connected to practically every mental health disorder we know of — especially depression and anxiety. In other words, when you don’t get enough sleep, you’re more likely to experience changes in your mental health and mood. The Great British Sleep Survey has found in previous research that sleep-deprived people are 7 times more likely to experience feelings of helplessness and 5 times more likely to feel lonely than people who get the recommended 7-9 hours of sleep each night.
  4. Humans are 60% more emotionally reactive when sleep deprived. The amygdala is responsible for triggering emotions, and it is excessively reactive when sleep deprived. We also lose some control from the prefrontal cortex – a part of the brain that is normally our rational and decision-making center. (NCBI)
  5. Guinness World Records no longer recognizes “lack of sleep” as a category because long term sleep deprivation is thought to pose serious health risks, both physically and mentally.
  6. Sleep evangelist, Matthew Walker, argues that the cognitive, emotional and physiological stresses of sleep deprivation take a toll on frontline personnel, such as military fighters, first responders, commercial airline pilots, and long-haul truck drivers — leading to an increase in vehicular accidents, botched surgeries and fatalities, and in the case of exhausted parents, child neglect and abuse.
  7. Men who only sleep 5-6 hours a night have a level of testosterone that’s 6-10 years their senior.
  8. According to a National Sleep Foundation poll, about ⅓ of women say their sleep is disturbed when they have their periods, and lack of sleep can exacerbate PMS symptoms like bloating, cramps, and discomfort.
  9. People who get 5 hours of sleep are 60% more likely to have a physical injury than those who get 9 hours of sleep. More specifically, lack of sleep can lead to a number of disorders, including but not limited to: microsleep, restless leg syndrome, cognitive dysfunction, anxiety, alcohol abuse, and cardiovascular risk. All of these health issues can subsequently cause physical injuries. Athletes have also been shown to experience a higher risk of injury when they do not get enough sleep the night before.
  10. When you don’t get the proper amount or quality of rest each night, you’ll experience lower peak muscular strength, lower vertical jump height, and lower peak running speed.
  11. Sleep deprivation typically causes people to feel hungrier. This is because their leptin levels drop, which subsequently causes an increase in appetite.
  12. Being awake for 16 hours straight leads to drowsiness and is almost equivalent to having a blood alcohol level of .05%. Note: the legal blood alcohol limit is .08%.
  13. Stress and sleep are incredibly interconnected. When we’re sleep-deprived, cortisol (a stress hormone) is released in our brain and in our bodies. And when stress rises and becomes cumulative during the day, it’s much harder to fall asleep at night because it’s harder to slow down and quiet our brains. (Arianna Huffington)
  14. 51% of active duty U.S. Army, Air Force, and Navy personnel have obstructive sleep apnea and another 24% suffer from insomnia. (
  15. Without adequate sleep and rest, overworked neurons can no longer function to coordinate information properly, and we lose our ability to access previously learned information. (Harvard)
  16. People with insomnia are 10 times more likely to have depression, and 17 times more likely to have anxiety. (NCBI)


Sleep and External Cues

  1. Just like our ancestors, our bodies naturally know when to wake up, eat, exercise and sleep based on what time of day it is (a.k.a. the positioning of the sun). But humans have since evolved (greatly!) beyond relying on sunlight or candlelight thanks to the development of artificial light — like LEDs, compact fluorescents (CFLs), halogens and incandescents. Today’s world doesn’t necessarily prioritize sleep as our ancestors did. Instead, society encourages people to be “on” all the time thanks to the lighting in our homes, office buildings, and public spaces. We also have nifty devices that use LED screens (smartphones, laptops, computers, tablets, televisions) that we can use on the go — whenever and wherever we want to. That means our bodies are constantly being exposed to artificial light sources, which makes your brain think that there’s daylight outside when there may not actually be. This is ok if you’re looking at your smartphone’s screen at noon, but if you’re looking at the screen at midnight (or any time after dusk), then it’s going to be tough for your mind and body to fall and stay asleep.
  2. While technology gives us power at our fingertips, the noise, light, and stimulation associated with digital devices — particularly at night — does without a doubt affect the quality and quantity of your sleep. More specifically, devices that have LED screens emit blue light, which the brain interprets as daylight. So if you’re staring at your smartphone a lot, and/or using it late into the evenings, then you’re more likely to lay awake in bed with a “wired and tired” feeling.
  3. It’s a good idea to turn your bedroom into a cave-like environment at night as you’re winding down to get ready for bed. This means:
    1. using blackout curtains to prevent any light leakage (from street lights, car headlights, airplanes, etc.) from entering your bedroom window(s)
    2. covering up the power source lights (specifically blue and green lights) that you typically find on monitors, power cords or other electronic devices with tape or stickers
    3. dimming the lights in your room in the hours leading up to bedtime, and turning them completely off when you’re ready to go to sleep
    4. wearing blue light blocking glasses that are specifically designed to block blue (and green) light at night — especially if you’re someone that likes to read on their tablet or work on their computer in bed
    5. keeping the room cool so that your body is comfortable enough to fall asleep (remember that your ancestors slept as it got cooler outside too!)

Shift Work

  1. Shift work (working outside of the standard 9-5 window) puts individuals at risk of experiencing something called Shift Work Sleep Disorder, which is characterized as having insomnia or excessive sleepiness.
  2. Shift Work is thought to be so disruptive to circadian rhythms that it’s often listed as a carcinogen. Carcinogens are substances and exposures that can lead to cancer. Some carcinogens do not affect DNA directly but lead to cancer in other ways. For example, they may cause cells to divide at a faster than normal rate, which could increase the chances that DNA changes will occur. (American Cancer Society)
  3. Many of today’s shift workers have some of the most dangerous jobs out there, including: doctors and nurses, EMTs, police officers, security workers, pilots, construction workers. Customer service representatives, commercial drivers, and other industries that require 24-hour coverage also fall into the shift category, and all of these jobs face the risk of worsened concentration, more accidents or errors happening, as well as higher injury and fatality rates.
  4. Shift workers are at increased risk for a variety of chronic illnesses such as cardiovascular and gastrointestinal diseases. (International Classifications of Sleep Disorders)
  5. Shift workers are at very high risk for colon cancer. This is because they tend to eat late into the night, and have altered circadian rhythms – never really giving the gut the rest it needs. (Satchin Panda)
  6. If you stay awake for three hours or longer between 10:00 PM and 5:00 AM for 50 nights in a year, then you are considered a card-carrying shift worker. (Dr. Satchin Panda)
  7. Sleep deprivation is a deep-rooted part of soldier culture. In the past, the popular “four-hour rule” stipulated that troops working in high-tempo, operational environments could function on only four hours of sleep. Today, thankfully, more and more members of the military recognize that this simply isn’t the case: Working under any circumstances with only four hours of sleep will lead to poor performance and weakened cognitive abilities (aka the brain-based skills we need to carry out tasks). (
  8. Put frankly, the body never adjusts to shift work!

Fun (And Some Not So Fun) Facts About Sleep

  1. After one week of short sleep, your blood sugar levels are disrupted so significantly that your doctor would prescribe you as being prediabetic.
  2. In the spring, when we lose one hour of sleep, we see a subsequent 24% increase in heart attacks. In the fall, when we gain an hour of sleep, we see a 21% decrease in heart attacks. That’s how fragile your body is to even just the smallest changes in your hours of sleep. (Matthew Walker)
  3. In the 1940s, studies showed that three-quarters of Americans, including college students, reported “rarely” or “never” seeing any color in their dreams. (People over 55 today grew up with little access to color television.) Now, those numbers are reversed, and a very small percentage of people dream in only black and white. (New York Times)
  4. In 1938, a sleep researcher and a student lived in a cave for over one month in order to study their own sleep cycles. This became known as the Mammoth Cave experiment, and it was a huge step towards identifying the human circadian rhythm. (The Scientist)
  5. Scientists still don’t know if animals dream during REM sleep the same way that humans do.
  6. If it takes you less than 5 minutes to fall asleep at night, then you’re probably sleep-deprived. It *should* take you about 10 to 15 minutes on average to fall asleep.
  7. Most people aren’t actually night owls, but their tendency is to stay up late because they drink coffee too late in the day and/or they are exposing themselves to too much blue light too close to bedtime.
  8. Snoring is the primary cause of sleep disruption for approximately 90 million American adults; 37 million on a regular basis. (National Sleep Foundation)
  9. Nearly 9 million are using prescription sleep medication. (Centers for Disease Control and Prevention)
  10. According to Business Insider, 90% of 18-29-year-olds sleep with their smartphones, and studies show that people who consume electronic media in bed are at higher risk for insomnia.
  11. A Harvard Medical School study found that 1 in 4 U.S. workers has insomnia, costing U.S. employers over $63 billion in lost productivity each year.
  12. One in four women has some insomnia symptoms, such as trouble falling asleep, trouble staying asleep, or both. (NCBI)
  13. Women may be more likely to have insomnia than men because they experience unique hormonal changes during:
    1. their menstrual cycle, especially in the days leading up to their period.
    2. pregnancy, due to discomfort, leg cramps, or needing to use the bathroom.
    3. perimenopause and menopause, because of hot flashes and night sweats.
  14. When you fall asleep in an unfamiliar environment, half of your brain stays awake as a protection mechanism. This is because your brain senses that it should be a little more on-guard than at home. So only half of the brain will achieve deep Non-REM (NREM) sleep.


Sleep and Medications

  1. Sleeping medications can help people get a decent night’s rest, but they are notably not designed for long-term use. (Harvard)
  2. If you have a short-term sleep disorder — a need to re-establish normal sleep patterns — then there’s an obvious reason to use sleep medications. But most doctors recommend not using sleeping aids for longer than a week or two.
  3. Possible side effects of using sleep medications include, but aren’t limited to:
    1. Sleepwalking
    2. Amnesia
    3. Impaired senses that could cause more risk of injury
    4. Increased risk of falling down
    5. “Rebound insomnia”, dependency, and/or trouble weaning off of the medication
    6. Shortened breath while sleeping
  4. Prescription sleep medications are big business — more than $41 billion/year in the U.S. Still, many people that have trouble sleeping rely on over-the-counter antihistamines such as Tylenol PM and Benadryl. (Consumer Reports)
  5. Your dreams might seem more real or vivid when you’re getting off of medication because your brain is not used to dreaming, so your brain is treating those dreams like a whole new experience. (Dr. Michael Breus)
  6. It can be difficult for people to stop taking sleep aids if they develop a dependence on them. When the medicine is taken away, people can get a temporary withdrawal reaction that makes it harder for them to fall and stay asleep.
  7. Melatonin in pill form is not the same thing as the melatonin that your body produces naturally. Although it is considered a natural sleep aid, it doesn’t work the same for everyone, and has its own potential side effects to consider before consuming:
    1. Nausea
    2. Headaches
    3. Dizziness
    4. Morning drowsiness
    5. Vivid dreams
    6. Changes in blood pressure
  8. Women tend to metabolize sleeping pills slower than men do, but they are often still prescribed the same or similar dosages.
  9. The number of emergency room visits involving overmedication of prescription sleeping pills in the U.S. almost doubled between 2005 and 2010, increasing from 21,824 visits in a two-year period to 42,274. Females accounted for two-thirds of those visits. (Women’s Health Magazine)
  10. Prolonged use of sleeping pills can make you more susceptible to memory loss.
  11. Studies found that elderly people who are prescribed sleeping pills become more prone to develop Alzheimer’s disease.
  12. A recent study showed that people with prescriptions for sleeping pills have an increased risk of developing lymphoma, lung cancer, colon, and prostate cancer. (Consumer Reports)
  13. People who take sleeping pills are significantly more likely to be diagnosed with cancer or to die within the next two and a half years than people who don’t take them. (Consumer Reports)


Sleep Hacks

  1. Be mindful of your exposure to artificial lighting:
    1. Go outside in the morning to help jumpstart your circadian clock.
    2. Wear blue light blocking glasses during the day to prevent overexposure to blue light from fluorescents, LEDs, and devices with LED screens.
    3. Wear sleep-hacking glasses at night that block all sleep-stealing wavelengths of junk light (blue, green and violet) leading up to bedtime.
  2. While traveling, particularly across time zones, proactively adjust your body clock to the local time in your destination. More specifically, focus on sleeping and eating according to the local time in order to avoid jet-lag.
  3. Turn your bedroom into a cave-like environment at night:
    1. Use blackout curtains to prevent light leakage from cars and street lighting outside.
    2. Dim the lights or turn them completely off so that your brain and body understand that it’s time to wind down and get ready for bed.
    3. Cover up pesky little lights like those found on power sources, computer monitors and tv screens with TrueDark® Dots.
  4. You can track and measure your sleep at night and then see how that translates to your performance and activity levels during the day with products like Oura Ring and SleepScore.
  5. You can also contribute to circadian rhythm research by tracking your sleep, diet, and exercise with the My Circadian Clock app.

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