Topic Review: Sleep – Part 1
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TOPIC INTRO
US President Donald Trump gets just four hours of sleep each night. Winston Churchill on the other hand, cherished his ~7hrs of sleep. Every afternoon Churchill would sip whisky and take a long nap that allowed him to stay up late into the night leading Britain to victory in World World II.
Leonardo da Vinci, a creative genius, is claimed to have functioned on just 1.5 hrs of sleep a night (although this is unverified). Meanwhile innovator Benjamin Franklin was a big sleeper, once saying “Early to bed, and early to rise makes a man healthy, wealthy and wise.”
Sleep habits vary widely for each us. It’s an elusive, somewhat mystical force in our daily lives. We all need sleep, but it depends on many individual variables that are often out of our control. Beyond cherry-picking a few famous people’s sleep habits, what is the latest on sleep science for all of us? We at Metafact are here to help.
Sleep is too big of a topic for just one review. In this first review on Sleep, we investigate the most common sleep questions and how they relate to our health. How much sleep do we need? What can lack of sleep cause? Can you die from lack of sleep? Can you get too much sleep?
Part II of our review on sleep will investigate the methods and tools we can use to help us get better sleep. Before then, let’s dive in with the world’s top sleep researchers and learn the latest on the science of sleep and human health.
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NUMBERS
Meta-Index
33% Proportion of human life spent sleeping
$327,000,000 Funding dedicated to sleep research in 2017 by the US National Institutes for Health
12.1: number of hours cats sleep a day
2.9 number of hours horses sleep a day
82.9% Proportion of day sleeping for a brown bat
7.9% Proportion of day sleeping for a giraffe
4 Typical number of sleep cycles (N1, N2, N3 and REM) that occur each night for humans
7 typical time in minutes for the first stage of sleep (N1) where you start to nod off.
25 typical time in minutes for the second stage of sleep (N2) where your muscles become more relaxed.
40 typical time in minutes for the third stage of sleep (N3) where it’s very difficult to wake someone up. Sometimes called ‘Deep Sleep’.
25% proportion of sleep taken up by the 4th stage of sleep, Rapid Eye Movement (REM). Eyelids flutter, dreaming and breathing becomes irregular. Your brain paralyzes your muscles so you do not act out the dreams.
6 Number of dreams experienced each night
97% Proportion of dreams forgotten each night
ORIGIN STORY
The Mystery but importance of Sleep
Since Nyx, the goddess of night in Greek mythology, was said to have given birth to both Thanatos (the god of death) and Hypnos (the god of sleep), humans have considered sleep to be just as mysterious and puzzling as death. Some even called death the “eternal slumber.”
Sleep is also commonly tied to death in popular culture. Even the common phrase “rest in peace” suggests that death is simply a permanent rest. This inherent sense of mystery surrounding sleep also lends a natural curiosity that drives us to seek answers for what happens to our brains while we sleep and why we fall asleep to begin with.
Sleep does more than simply replenishing our energy levels. Our brains can use sleep and the state of dreaming to make sense of the events of our waking lives. A good night’s sleep can improve our mental health and increase our life span. Throughout human history, plenty have attempted to explain how or why this happens, and yet very few concrete answers have come to light in that time.
As societies formed, sleep began to pose a threat to so-called “productivity” – if people slept too much or too often, societies would lose structure and hierarchies became unstable. However, if they did not sleep enough, the quality of their work would suffer. We were then left with the responsibility of attempting to structure sleep within society.
In 1913, a French scientist named Henri Pieron wrote a book entitled “Le probleme physiologique du sommeil,” which was the first written text to look at sleep from a physiological perspective. This was the foundation for modern sleep research, and led to the 1953 discovery of Rapid Eye Movement (REM) during sleep. Aided by technology and data, sleep research has expanded rapidly in recent decades, giving scientists unparalleled insights into the importance of sleep for human health.
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EXPERT EXPLAINER
Why do we need sleep?
James Ware: A sleep expert from Eastern Virginia Medical School in Sleep Research
Sleep is homeostatic (naturally self-regulating to reach a stable state) and adaptive with an expected range for most people of 6-9 hr. Each person has a sleep set point, which the body tries to maintain. Too little sleep results in sleepiness. Too much leads to more time awake at night.
For most adults, the set point is about 7.5 hours. However, one’s immediate sleep needs and therefore sleep time appropriately fluctuates in response to internal and external happenings. For example, after heavy exercise some sleep a bit more possibly due to inflammatory / soporific cytokines.
Fortunately, we can sleep less to complete tasks, e.g., completing a report. Too much sacrificing sleep for other task contributes to a sleep debt along with cognitive and physiological problems. Fluctuations in sleep can be due to the brain and muscles responding to the day’s activities, infection, noisy neighbors or even changes in the microbes of the gut.
Frequent perturbations or a lot of time spent outside of the normal physiological set point interfere with the functions of sleep and our circadian rhythms. Thus, chaotic sleep can impair most body functions including metabolic, cardiovascular, immune, and cognitive activity. It is not possible for a healthy person to “overdose” on sleep. The person will instead lie awake, usually uncomfortably, in bed or get up.
Sleeping too much is a strong warning sign of a problem and deserves discussion with a doctor. It is our canary in the coal mine. This recognition hopefully leads to changes that can forestall death!
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META-TRENDS
Hours slept per night by age and gender
ATLAS | Data: Walch et al, Science (2016)
META-TRENDS
Population sleeping less than 7hours per night in US (%)
ATLAS | Data: CDC
META-TRENDS
How many hours should I sleep?
THE CONSENSUS
Is lack of sleep linked to higher mortality?
100% Affirmative from 10 experts
Read the full answers to this question here. Extreme sleep depravation is fatal for animals. “Studies on mice have shown that complete sleep deprivation kills them within a week or two” writes Dr Zahra Moussavi, sleep expert from the University of Manitoba. For humans, we should get 7-9 hours of sleep. However, what happens if you don’t get the recommended daily dose? Is lack of sleep linked to early death?
There was unanimous agreement amongst our experts. If you get 6hrs of sleep or less, “evidence suggests an increased risk of all-cause mortality” notes Dr Tetyana Kendzerska, an expert in sleep research from the University of Ottawa. Experts suggest a clear link between poor sleep and early death but a causal effect is still debatable. “Mortality is a complicated outcome” writes Dr Jason Wong, an epidemiologist from the National Cancer Institute, “there are many forms of mortality related to hundreds of different cancers, cardiovascular disease, deaths of despair, metabolic disease, accidents etc”. To draw a direct line of cause-and-effect between sleep and mortality is impossible given the current literature he says.
The key question is whether sleep causes certain diseases or is rather, influenced by those conditions. Some new insights may offer a plausible explanation for the link. “Growing data in well controlled trials have found that sleep deprivation leads to pathophysiologic changes that result in worsening metabolic and cardiovascular outcomes (i.e. diabetes risk, weight gain, hypertension) that could be mediators for higher mortality rates” writes Dr Dennis Auckley, an expert in sleep research from Case Western Reserve University.
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THE CONSENSUS
Are children and teenagers getting less sleep?
92% Affirmative from 14 sleep experts
Read the full answers to this question here. “Shorter sleep duration in young children is associated with an increased risk for later obesity” notes pediatrician Dr Joanna Maclean from the University of Alberta. For good health, school-age children (6-13yrs old) need 9-11 hours every night while teenagers (14-18yrs old) need 8-10 hrs per night. But are children and teenagers getting enough sleep? No – there was a clear consensus on this trend.
53% of school-age children don’t get enough sleep notes Dr Cele Richardson, a sleep scientist from the University of Western Australia, with a recent US study showing “the proportion of adolescents regularly obtaining less than 7 hours of sleep increased from 1995 to 2012”.
Sleep epidemiologist from the University of Southern Florida Dr Chighaf Bakour shares evidence from a study of nearly 700,000 that showed over the last century, children and teens are getting 1 hour per night less sleep than those 100 years ago. So what is causing the decline in sleep?
The invention of lighting, earlier school schedules, two working parents, sports activities after school, homework demands and limits on recreational space availability have all contributed to pushing back bedtimes and earlier wakeups notes pediatrician Dr Joanna Maclean. “Screens are smaller, more ubiquitous, and also associated with shorter sleep duration,” she writes.
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THE CONSENSUS
Is too much sleep bad for you?
Read the full answers to this question here. Although too little sleep certainly seems to have a negative effect on our health, what about too much sleep? Many experts refer to something called a “U shaped curve” in terms of sleep and risk levels for diabetes and cardiovascular disease. Our experts agree that too much sleep can be just as bad for your health as not enough sleep – but not in the short term. “There is no evidence of negative health consequences if habitual sleep duration is experimentally increased for a week or more in healthy individuals” writes Dr Monika Haack from Harvard University. In fact, she says, extending habitual sleep can be beneficial on everything from blood pressure to pain sensitivity.
If you are sleeping >10hrs for an extended period, it may be a sign of other health problems. If that is you, best to check with your doctor our experts suggest.
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THE CONSENSUS
Is there such a thing as sleep debt?
83% Affirmative from 6 experts
Read the full answers to this question here. Say that you didn’t get enough sleep last night. According to science, would you be able to “make up” that sleep tomorrow night?
Some experts say that this is unlikely due to the physiological purpose that different stages of sleep serve. Dr Jim Horne, sleep researcher from Loughborough University, says that when you lose sleep, you often lose the “deep sleep” that you can only get by sleeping for long periods of time. “In sum,” Horne writes, “it’s the quality of sleep that counts, here, rather than quantity.” It also should be noted that just because a survey indicates that people want more sleep does not necessarily mean that they need more sleep. Eating, drinking — and yes, sleeping — to excess is possible without necessarily having the need for any of those things. Our sleep is more adaptable than we previously thought.
However, many experts argue that a so-called “sleep debt” does, in fact, exist. Dr Stanley Coren, an expert from the University of British Columbia, wrote a book called “Sleep Thieves” that reviews a number of sleep studies examining sleep debt. Over the course of these studies, the general finding was that people tested on IQ scored lower after getting less sleep. Interestingly, these effects accumulated over time. “If an individual lost two hours of sleep per night over a five night period, then at the end of this period they would effectively be operating at a level which on the tests amounted to a 15 point loss of IQ,” Coren writes. Therefore, a “sleep debt” does exist in terms of cognitive functioning. Unfortunately, these studies fail to answer whether or not this debt can be made up.
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THE CONSENSUS
Is there a proven link between poor sleep and dementia / alzheimers?
100% Affirmative from 12 experts
Read the full answers to this question here. Given that poor sleep appears to affect cognitive functioning and memory, it would make sense to question whether or not sleep deprivation could lead to conditions that affect those areas of the brain, like dementia and Alzheimer’s.
Dr Fabricio Ferreira de Oliveira, an expert in neurology from the Federal University of São Paulo, says that “sleep disturbances increase with advancing dementia severity, and may predict faster cognitive decline.” However, much like with other effects of sleep deprivation, we do not currently have the information necessary to determine whether a lack of sleep contributes to dementia or if insomnia is simply a side effect of the later stages of the condition.
“Sleep is important for neuronal plasticity, memory consolidation, and has also been shown recently to facilitate the elimination of toxic molecules such as beta-amyloid peptides.” says Dr Laurent Seugnet, an expert in sleep research from Inserm in France. Therefore, it can be assumed that there is a relationship between sleep disorders, which disrupt healthy sleep, and the occurrence of dementia and Alzheimer’s.
Although a relationship is clearly present, given the limitations of the current available evidence, it is hard to say whether a lack of sleep causes Alzheimer’s or vice-versa. Dr Bettina Platt, an expert in neurodegenerative disease from the University of Aberdeen, calls it a “chicken and egg” dilemma: “does sleep disturbance cause / contribute to dementia, or does dementia lead to sleep disturbance?”
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QUICK ANSWERS WITH CONSENSUS
Is sleep quality in decline? Uncertain. These studies suggest that poor sleep quality is associated with cognitive decline and health issues, particularly in older adults.
Can a lack of sleep increase your chance of developing diabetes? Likely. These studies suggest that insufficient sleep duration and poor sleep quality are associated with an increased risk of developing diabetes.
Does lack of sleep impact memory? Likely. These studies suggest that lack of sleep negatively impacts memory, affecting attention, working memory, memory consolidation, and the ability to retain new information.
Is lack of sleep dangerous? Yes, particularly for driving and shift workers. These studies suggest that lack of sleep is dangerous, as it is associated with increased risks of metabolic and cardiovascular diseases, cognitive impairment, negative mental health outcomes, and safety hazards.
Is lack of sleep bad for your heart? Likely, it may increase ‘inflammatory processes’. These studies suggest that lack of sleep is bad for your heart, increasing the risk of cardiovascular diseases, morbidity, and mortality.
Does sleep affect your immunity? Likely. These studies suggest that sleep significantly affects immunity, with sleep deprivation generally weakening immune responses and increasing infection risk.
Is 8-hour sleep unnatural for humans? No. Sleep patterns are diverse across cultures. Some studies suggest that 8-hour sleep may not be necessary for all individuals, while other studies indicate that reduced sleep can have negative health effects.
Does radiation from sleeping next to your smartphone affect your brain patterns negatively? Unlikely. Some studies suggest that radiation from sleeping next to your smartphone can negatively affect brain patterns and sleep quality, while other studies indicate no significant impact on cognitive tasks or direct sleep disruption.
Are sleep disorders associated with cognitive decline? Likely. These studies suggest sleep disorders are associated with cognitive decline.
Is it possible to read dreams with a brain scan? Unlikely. These studies suggest that while current technology can infer and predict some aspects of dream content from brain activity, it is not yet capable of fully reading dreams.
Do dreams reflect unconscious desires? In some dreams, yes. These studies suggest that dreams reflect unconscious desires.
NOTABLE ANSWER
Can you learn in your sleep?
Itamar Lerner: An expert from University of Texas at San Antonio in Neuroscience, Sleep Research
Probably yes. While past aspirations for finding ways to learn complex new information (e.g., learning a new language) during sleep have turned out to be naive or unrealistic, simple strengthening and reorganization of previously learned materials may be possible.
A new technique developed over the last decade, Targeted Memory Reactivation (TMR), involves having subjects learn new materials to memorize, or perform a certain task, while at the same time being exposed to some unrelated external stimulation (auditory tones, odors, or even small electric currents induced to the scalp). This concurrent presentation supposedly creates associations between the task being learned and the unrelated stimulations. During a following sleep period, the same external stimulations are applied again, at specific times during the sleep cycle.
Evidence from animal research suggests that these repeated presentations reactivate memories related to the learned task, leading to their strengthening. The following morning, subjects who receive such targeted stimulations show improved memory for the learned materials, or better performance in the learned task, compared to subjects that receive sham stimulations (For a recent review, see Cellini & Capuozzo, 2018)
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TAKEAWAYS
- How much sleep you need per night depends on the individual – but on average your body would naturally like to have ~7.5hrs (6-9hrs for most)
- Poor sleep is linked to diabetes, heart and neuro-degenerative conditions like Alzheimer’s Disease
- Children and teenagers are getting ~1hr less sleep than previous generations
- Getting less than 6hours and more than 10hours is linked to earlier death – but a causal effect is unknown
- You can’t make up temporary “sleep debt“. It’s better to just get enough sleep the first time around
- If you are sleeping >10hrs for a long period, see a doctor
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