The Science of Sleep and Sleep Deprivation

Written by Dr. Joseph Mercola Fact Checked

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Story at-a-glance -

  • Healthy sleep consists of several stages, each stage lasting five to 15 minutes, with a complete cycle taking between 90 and 120 minutes. You cycle through each of these stages four to five times during the night
  • Getting less than six hours of sleep in any given 24-hour period will leave you cognitively impaired. In 2013, drowsy drivers caused 72,000 car accidents in which 800 Americans were killed and 44,000 were injured
  • Polls show 63 percent of people do not get enough sleep to be healthy, 69 percent struggle with frequent sleep problems and 22 percent are so sleepy during the day it affects their quality of life
  • Sleep deprivation costs the U.S. economy $411 billion each year in accidents and lost productivity, equivalent to 2.28 percent of the gross domestic product
  • Recent research found people who got seven hours of sleep each night had hearts showing signs of being 3.7 years older, based on biological age, than their chronological age; those who got five hours or less had the oldest biological heart age — 5.1 years older than their chronological age

Sleep deprivation can have a number of health effects and ramifications, ranging from mild to devastating. The 2015 National Geographic video, "Science of Sleep," starts out with the story of third mate Gregory Cousins, whose sleep deprivation led to one of the greatest environmental catastrophes in history.

Cousins had slept only six hours in the past 48 hours when he ran the supertanker Exxon Valdez aground, causing the 11 million gallons of crude oil to spill into Prince Williams Sound, devastating 23 species of wildlife and nearly 13,000 miles of shoreline habitat.

Indeed, research shows getting less than six hours of sleep in any given 24-hour period will slow your reaction time and leave you cognitively impaired, unable to make rational decisions. This is a devastating combination, and accident statistics offer sobering reminders of the seriousness of the situation.

In 2013 alone, drowsy drivers caused 72,000 car accidents in which 800 Americans were killed and 44,000 were injured.1 This is more than died from those texting and drunk drivers combined.

Sleep Deprivation Is a Recipe for Serious Accidents and Puts Lives at Risk

According to the American Sleep Association,2 nearly 40 percent of people report unintentionally falling asleep during the day at least once a month, and nearly 5 percent have nodded off while driving. Most people skimp on sleep because they feel they have to "get things done." However, the evidence clearly shows that what you end up with is the complete opposite of productivity.

Sleep deprivation is actually costing the U.S. economy $411 billion each year in accidents and lost productivity3 — an amount equivalent to 2.28 percent of the gross domestic product. An estimated 1.2 million working days are also lost.

In worst case scenarios such as the Valdez oil spill and the space shuttle Challenger accident, life is lost. The latter is described in the 1988 paper "Catastrophes, Sleep and Public Policy: Consensus Report," published in the journal Sleep.4 Other costly accidents caused by sleep-deprived personnel include the Three Mile Island nuclear power plant accident and the Mir space station collision.

Polls show 63 percent of people do not get enough sleep to be healthy, 69 percent struggle with frequent sleep problems and 22 percent are so sleepy during the day it affects their quality of life. Still, most say they will simply push through their sleepiness in order to complete whatever it is that needs to be done.

But when construction workers, nurses, doctors, mechanics, pilots or truck drivers, for example, go to work and "push through," it can have lethal consequences for those around them. Needless to say, sleep deprivation itself is also hazardous to your health and is perhaps one of the fastest ways to break down your immune function and make yourself sick.

Research by Eve Van Cauter, director of the Sleep, Metabolism and Health Center at the University of Chicago, also shows that sleeping less than six hours a night dramatically increases your risk of insulin resistance, which is at the core of most chronic diseases.

As noted in "Science of Sleep," research conducted in the 1980s discovered that depriving mice of sleep for 17 days straight led to certain death. Two contributing causes were immune system breakdown and blood poisoning.

Lack of Sleep Ages Your Heart

Studies have linked poor sleep with a variety of health problems, including excessive aging of your heart. People who got seven hours of sleep each night had hearts showing signs of being 3.7 years older, based on biological age, than their chronological age.5

People who regularly slept either six or eight hours had hearts that were on average 4.5 years older than their chronological age, while those who got just five hours or less of sleep each night had the oldest biological heart age — 5.1 years older than their chronological age.

As noted by lead author Quanhe Yang, senior scientist in the Division for Heart Disease and Stroke Prevention of the U.S. Centers for Disease Control and Prevention:6

"The difference between a person's estimated heart age and his or her chronological age is 'excess heart age.' Higher excess heart age indicates a higher risk of developing heart disease.

For example, if a 40-year-old man has a heart age of 44 years based on his cardiovascular risk profile — the personal risk of having a heart disease — then his excess heart age is 4 years. In effect, his heart is four years older than it should be, for a typical man his age. The concept of heart age helps to simplify risk communication."

Of the 12,755 participants in this study, 13 percent slept just five hours or less per night; 24 percent got six hours; 31 percent got seven hours; 26 percent slept for eight; and about 5 percent got nine or more hours of sleep each night. Considering the ideal sleep time is between seven and nine hours, these statistics reveal at least 37 percent of American adults aren't getting anywhere near healthy amounts of sleep.

Sleep Quality Also Affects Blood Pressure and Heart Disease Risk

Other recent research7 strengthens the link between sleep problems and heart disease. While this link has been previously noted, recent research found that even if you sleep a healthy number of hours, the quality of that sleep can have a significant impact on your risk for high blood pressure and vascular inflammation associated with heart disease.

Women who had mild sleep disturbance such as taking longer to fall asleep or waking up one or more times during the night were "significantly more likely to have high blood pressure than those who fell asleep quickly and slept soundly," Forbes reports.8 According to the researchers:9

"Systolic blood pressure was associated directly with poor sleep quality, and diastolic blood pressure was of borderline significance with obstructive sleep apnea risk after adjusting for confounders. Poor sleep quality was associated with endothelial nuclear factor kappa B activation.

Insomnia and longer sleep onset latency were also associated with endothelial nuclear factor kappa B activation … These findings provide direct evidence that common but frequently neglected sleep disturbances such as poor sleep quality and insomnia are associated with increased blood pressure and vascular inflammation even in the absence of inadequate sleep duration in women."

Different Stages of Sleep and Their Importance

Sleep is not a single state. Healthy sleep consists of several stages,10 each stage lasting five to 15 minutes, with a complete cycle (light, deep and rapid eye movement or REM sleep) taking between 90 and 120 minutes.

A full sleep cycle starts out in light sleep and progresses through to deep sleep, then reverses back from deep to light sleep before entering REM. You cycle through each of these stages four to five times during the night, and this cycling is tremendously important, from both a biological and psychological perspective.

Stages 1 and 2 (light sleep; non-REM) — During the initial stages of sleep, biological processes in your body slow down but your brain remains active as it begins the editing process where decisions are made about which memories to store and which to discard.

Stages 3 and 4 (deep sleep; non-REM) — In these deeper sleep stages you enter into a near coma-like state, during which physiological cleansing and detoxification processes in the brain11 take place. Your brain cells actually shrink by about 60 percent during this deep sleep phase. This creates more space in-between the cells, giving your cerebrospinal fluid more space to flush out the debris.

Stage 5 (REM) — During this last phase, you enter rapid eye movement (REM) sleep, where dreaming takes place. In this phase, your brain is as active as it is during wakefulness, but your body is paralyzed, which prevents you from acting out your dreams.

The frightening experience of sleep paralysis occurs when you awaken during this phase and find your body unresponsive. The "treatment" for this disorder is knowledge. As noted in "Science of Sleep," you simply need to be educated about what's happening so that you can calmly ride out the episode, which typically will not last more than a few minutes.

All of these stages are important, and it's important to cycle through them enough times each night — especially the deeper stages. When stages 3 and 4 are missing or interrupted, your brain gets clogged with debris associated with Alzheimer's disease and, indeed, sleep deprivation is a risk factor for severe dementia. Stages 1 through 4 are also what allow you to feel refreshed in the morning, while stage 5 is important for memory.

Sleep Deprivation Takes a Toll on Mental Health

Forgoing REM sleep for extended periods of time may also lead to a state where you actually start dreaming while you're awake, resulting in delusions and wild hallucinations. "Science of Sleep" features Dr. William Dement, a professor of psychiatry and behavioral sciences at Stanford, who in 1963 oversaw a sleep deprivation experiment by a young man named Randy Gardner.

"We were waiting to see if he would become psychotic," Dement says. Gardner stayed awake for a record 264 hours — 63 hours longer than Peter Tripp, a disc jockey who, in 1959, tried to break the world record for sleeplessness. Tripp stayed awake for 201 hours straight, doing a continuous broadcast from Times Square.

For Tripp, hallucinations set in on Day Three. He saw spiders in his shoes and became desperately paranoid, convinced people were trying to poison him. He also became belligerent and abusive, and according to one of the attending psychiatrists, "clearly psychotic."

Gardner, on the other hand, claims he was feeling all right up until the eighth or ninth day, and didn't start having hallucinatory experiences until the very end. Once the experiment ended, after 11 days of wakefulness followed by 14 hours of sleep, a comprehensive exam and mental health check was performed. Gardner was found to be completely normal.

According to Dement, Gardner's experiment proved extended sleep loss did not cause psychosis. Tripp's experiment, on the other hand, revealed that even though he was awake — walking around and talking — his brainwaves showed he was asleep, and it was during the REM cycles that he was most likely to hallucinate. Essentially, he was experiencing his nightmares in an awake state.

What's more, while Tripp had no signs of psychosis after the experiment ended and he'd slept for 24 hours, many insisted his personality had permanently changed for the worse. He was no longer as cheerful and easygoing as he'd been before, and those who knew him best insist those eight days of sleep deprivation damaged his psyche long-term.

In all likelihood, the effects of sleep deprivation will affect different people in different ways, depending on a variety of biological, environmental and perhaps even genetic factors.

The Influence of Genetics, Jet Lag and Stress Chemicals on Sleep

Sleep deprivation can be worsened by jet lag. Also known as flight fatigue, time zone change syndrome or desynchronosis, jet lag occurs when travel across time zones disrupts your internal body clock, resulting in daytime sleepiness and lethargy, nighttime insomnia, irritability, confusion and poor concentration.12,13

Interestingly, researchers have found that people with a genetically inherited sleep disorder called familial advanced sleep phase syndrome have a circadian body clock that runs about three hours faster than normal. According to "Science of Sleep," scientists are trying to determine the protein associated with this gene, in the hopes that it might be used to develop "jet lag drugs."

Whether or not such drugs will ever be realized, there are other, more natural ways to minimize the effects of jet lag. For tips and tricks, see "Can You Decrease Jet Lag With Exposure to Light?"

"Science of Sleep" also discusses research showing the role of stress chemicals in waking. Tests have revealed your body will begin to release certain stress chemicals about an hour before your intended wakeup hour, and that this occurs through mental expectation or intention alone. In other words, the stress chemicals act as a sort of internal alarm clock, readying your body to wake up at the time you mentally prepared yourself to get up.

General Sleep Guidelines

So, how much sleep do you need to optimize your mental and physical health? According to a scientific review of more than 300 studies published between 2004 and 2014, a panel of experts came up with the following recommendations. Keep in mind that if you're sick, injured or pregnant, you may need a bit more than normal.

Age Group Hours of sleep needed for health

Newborns (0 to 3 months)

14 to 17 hours

Infants (4 to 11 months)

12 to 15 hours

Toddlers (1 to 2 years)

11 to 14 hours

Preschoolers (3 to 5)

10 to 13 hours

School-age children (6 to 13)

9 to 11 hours

Teenagers (14 to 17)

8 to 10 hours

Adults (18 to 64)

7 to 9 hours

Seniors (65 and older)

7 to 8 hours

There's simply no doubt that sleep needs to be a priority in your life if you intend to live a long and healthy life. For many, this means forgoing night-owl tendencies and getting to bed at a reasonable time.

If you need to be up at 6 a.m., you have to have a lights-out deadline of 9:30 or 10 p.m., depending on how quickly you tend to fall asleep. As for how to improve your sleep if you're having trouble falling or staying asleep, see "Sleep — Why You Need It and 50 Ways to Improve It."