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Why We Sleep

The question arises of what exactly is the purpose of sleep.  The short answer is that we don’t know exactly.  However, as the science of sleep progresses, our understanding as to the true purpose of sleep will likely be elucidated.

The fact that in deep NREM sleep physical and mental activity slow down considerably, has led to the reasonable speculation that this phase of sleep serves as a recovery and recharging function. While lower species don’t have REM sleep, almost all species do have NREM suggesting that this phase of sleep has a restorative function. When you’re in NREM you’re recharging your batteries. More specifically, N3 sleep or deep sleep is felt to be the most restorative.

This recharging function is essential because a prime consideration of both the brain and body is energy production and conservation. The brain’s prime goal is survival and its primary defense system, the fight/flight system, uses a lot of energy. Thus the production and conservation of energy is a critical function and it is assumed that NREM fills this role. When people are deprived of NREM sleep they do continue to feel very tired and the body tries to compensate for this on subsequent sleep occasions.

If NREM is about energy conservation, what is REM? Paradoxically REM uses a lot of energy. Perhaps the NREM phase of recovery, mentioned above, is among other things, designed to ensure that there’s enough energy for the REM phase?

Some researchers have argued that because of the high energy output in REM, the energy conservation of sleep overall is pretty small, particularly compared to being awake and just resting. Others have pointed out that if restoration of energy was the purpose of sleep, large animals should require more sleep, but in fact they sleep less.

One view of the energy consuming REM phase of sleep is that its main function is the consolidation of memories formed during the day. This would be crucial for learning and indeed young children do seem to require more REM than adults. One metaphor that might be useful here is that during the REM phase of sleep, the brain is filing away the day’s events. As you open the relevant filing cabinet you will see other associated ideas and other relevant recent events and their associations. If that were the case, our dreams would involve recent events and associations these events have with past experiences. Of course, a lot of dreams are like that. Moreover, the dreamer’s emotional state at the time of the dream would likely shape the dream sequence. So it’s likely that some consolidation of memories occurs during REM sleep and this process helps to explain dreaming.

While the consolidation of memories might be an efficient use of sleep time, it doesn’t appear too critical to functioning. As mentioned above, many species don’t even have a REM sleep phase, and when REM is suppressed it doesn’t appear to affect basic functioning.  However, in humans, when REM is suppressed for while, as in heavy alcohol consumption, there is a period after the REM suppression in withdrawal, during which there is increased amounts of REM sleep, what is called REM rebound.

The evidence is not overwhelming but it is reasonable to assume that NREM sleep serves some energy restoration function and that NREM sleep serves some neural consolidation of memories and learning.

Now we have a better understanding of sleep, it has allowed us to research sleep patterns and determine the type, rate and costs of poor quality sleep, reduced sleep time, or a combination of both. And we have been unable to expose the myth, common until about 20 years ago, that sleep deprivation or poor quality sleep doesn’t cause serious health and economic consequences.

History of Sleep


History of Sleep
While it seems obvious that humans have slept throughout their history, the way they did so in the past might be different from how we sleep today. For example, in his famous Oddysey written around 800 BC, Homer writes about people having two very distinct periods of sleep at different times of the 24 hour cycle. About three hundred years later, the Greek Alcmaeon observed that blood seemed to be draining from the vessels as we sleep, and assumed that this was a cause of it. Similarly, around 400B.C., Hippocrates noted that bodies cool during sleep and that sleep was therefore characterized by blood retreating from the periphery. Not long after that, Aristotle suggested that sleep was brought on by the warming of the body through digestion. Of course, such an observation would be heavily influenced by what one was eating and drinking and certainly rich foods and plentiful amounts of wine could have people nodding off in no time.

Up until about 162 A.D., the view was that the heart, not the brain, was the center of influence from which all bodily actions were controlled. It was Galen who suggested that the brain was the body’s control center and not the heart, leading to sleep theories that were centered on brain rather than heart activity. Subsequent research suggests that the ancients weren’t totally wrong about the heart. It turns out that there are about 50,000 neurons (brain cells) in the heart that connect with the brain. And there are 500 million neurons in the gut, so perhaps Aristotle’s connection between sleeping and eating wasn’t entirely off the mark.

Despite Descartes’ effort during the Renaissance to divide mind and body, much of the subsequent work focused on the brain’s control of the sleep process. In 1650, Dr. Willis identified the functions of different parts of the brain; in 1929, Hans Berger invented the EEG, which opened the study of the brain and its activity. Later, various areas of the brain were identified with the specific functions of sleep.

Specific identification and treatment for sleep disorders emerged in the twentieth century. In 1903 the first sleeping pill was introduced and in 1930 the first stimulant treatment for narcolepsy was developed. Restless Leg Syndrome (RLS) was first described by a Swedish doctor in 1945 and other conditions were subsequently diagnosed; for example, Dr. Schenk and colleagues first reported on a group of patients who didn’t demonstrate the usual muscle paralysis when in REM. In the last seventy years, there has been even more research, which has been able to identify the different stages and phases of sleep.

Nathaniel Kleitman was one of the pioneers of sleep research, with an interesting personal history. Arriving in New York as a penniless 20-year-old in 1915, he went on to get a PhD and conduct some of the earliest research on sleep and the brain. Using a crude EEG machine that used about half a mile of paper each time it ran a sleep test, Kleitman noticed the different stages of sleep, especially dreaming sleep. In a 1953 paper, he and his colleague, Eugene Aserinsky, called this stage of sleep “Rapid Eye Movement.” Kleitman, who lived to be 104, was fascinated by the concept of wake/sleep cycles and even conducted research on the effects of sleeping in caves and submarines.

One of Kleitman’s proteges, William Dement, continued the tradition of researching the brain and sleep using EEG technology. Dement was interested in sleep dysfunction and has contributed enormously to the diagnosis and treatment of sleep disorders. He is widely considered the father of sleep medicine. He launched what is now known as the American Academy of Sleep medicine and served as president for twelve years. Dement also played bass as a jazz musician and has even played with musical greats, Ray Charles and Quincy Jones.

Dement formed the Stanford University Sleep Disorders Clinic which has been the home to a great deal of important sleep research and some other very influential researchers. One of these is Christian Guillemenault, a prolific researcher, who has written more than 600 academic papers. His most noted work has been on the subject of sleep apnea. He co-opted cardiologists to measure and observe blood pressure and cardiac function in people who have what we now know as sleep apnea. In fact, Guillemenault was one of the first to use the term ‘obstructive sleep apnea’ and was the first to use tracheostomies to free the airways, both providing relief to sufferers as well as convincingly demonstrating the relationship between apnea and cardiovascular function.

Despite the work of these pioneers, sleep medicine research and literature lagged behind that of the other key lifestyle behaviors, like nutrition and exercise. It is only in the past decade has there been a recognition of the importance of sleep, elevating it to a science more in keeping with its importance.

What is Sleep?


What is sleep?

Regardless of the various theories, we know that sleeping is a natural function common to all humans and animals, too. We are designed to function on a wake/sleep cycle, although with the advent of artificial light (thank you, Edison for the 1879 introduction of the light bulb), energy boosting drinks, foods and medications, that cycle can be severely disrupted. However, it is clear that daily sleep is the preferred default setting for humans and that sleeping serves some very important functions that underpin health and wellbeing. However, there isn’t a complete agreement on what the functions of sleep actually are.

Sleep can simply be described as a state of reduced sensory and environmental responsiveness and physical inactivity. By comparison, wakefulness is characterized by, sensory perception, thinking, environmental responsiveness and physical activity.

There are various stages of sleep in mammals; the two most prominent are Rapid Eye Movement (REM) and non-REM (NREM) sleep. These two phases are quite different.

In REM sleep, muscles are effectively paralyzed, what is called atonia, and dreaming occurs. Obviously, it’s a good design feature to be paralyzed while dreaming otherwise many of us would be sleep walking and acting out or dreams with physical actions. This atonia is achieved through muscle inhibition by parts of the brain that regulate movement.    Interestingly, there is a sleep disorder called REM Behavior Disorder which is characterized by individuals acting out their dreams.

In REM there is also an increase in breathing and heart rate variability. In addition, in REM the brain also uses a lot of energy, which is important because one theory of sleep is that it is about energy conservation, which might seem paradoxical. There is obviously a lot of mental activity in REM unlike in the other sleep phase, which has earned the REM phase of sleep “paradoxical sleep.”  Core temperature is less well regulated in REM but sexual arousal is common and independent of dream content. In other words, physiology comes first and arousal is experienced, which may or may not be incorporated into a dream’s content.

NREM sleep is characterized as featuring general immobility, regular respiration and heart rate, and slow mental activity. It is divided into three parts:

N1: falling asleep, just in that border between nodding off but still easily awoken

N2: breathing and heart rate slow as you drift off to sleep

N3:  the slow wave delta phase that characterizes NREM. The hallmark feature of N3 sleep is slow, high amplitude delta waves on EEG.  The first episode lasts 45-90 minutes but gets progressively shorter though the night. Children tend to have more N3 sleep than older individuals.

These two phases of sleep are so different that they have led to speculation that there is more than one function of sleep and those functions are represented by these quite different states.

In addition to these separate and distinct sleep states, there is also a typical pattern of sleep in humans as we move in and out of these different phases.

Brain Wave Activity

Delta: 1-4 cycles per second: Deep sleep. Typical NREM phase

Theta: 5-8 cycles per second: Conscious, but low level of brain activation, e.g. meditation.

Alpha: 9-13 cycles per second: Relaxed wakefulness

Beta: 14-30 cycles per second: Active processing, stress.

Sleep Cycles

Sleep occurs in cycles that typically last 90 minutes; the ultradian sleep cycle.  Sleep proceeds from NREM phase to a REM phase, about five times a night. There is typically more NREM in the earlier part of sleep and more REM in the later part of the night or early morning. This is why people commonly awaken during their dreams.  REM accounts for between 20% and 25% of total sleep time.

The way in which a person cycles through these phases, as well as the quality of the stages of sleep, determines the healthiness or otherwise of sleep. There are almost 80 distinct types of sleep disorders, which reflect different dysfunctions in the stages and phases of sleep.

Sleep and Mood Disorders

Sleep disturbances are commonly occurring complaints in people who are diagnosed with mood disorders.1 By far, the most common mood disorder is depression.  It is estimated that 6.7% of the US adult population meets criteria for major depression each year.  The majority of individuals with major depression will have sleep related complaints of complaints of fatigue.

Changes in patient’s sleeping patterns are criteria which help to make the diagnosis of these mood disorders. This emphasizes the importance of how common these sleep disturbances occur in patients with mood disorders. Up to 16 percent of the general population struggles with insomnia (the inability to fall asleep), but this percentage increases in patients with mood disorders.  It is estimated that up to 80% of patients diagnosed with major depression have symptoms of insomnia.  In addition, the symptoms of sleepiness, fatigue, anhedonia, and difficulty initiating or maintaining sleep are very common in both insomnia and depression.  Therefore, the diagnosis of major depression should be made with caution in patients who don’t present with this sleep disorder.2

Major depression

Major depression is characterized by at least two weeks of low mood that is present in most situations. Affected individuals may also complain of experiencing low self-esteem, low energy, a loss of interest in activities that used to be enjoyable, and pain without a definitive cause. Some people may also admit to thinking false beliefs they believe are true (delusions), or they may even hear or see things that others cannot (hallucinations).

Major depression negatively affects an affected person’s personal and work, or school life, as well as their general health, eating and sleeping habits.  One of the main characteristic of major depression is that it affects the hypothalamus in the brain. This is an area of the organ that is responsible for connecting the brain to the endocrine system (responsible for the release of hormones which control metabolic functions of the body). Major depression negatively affects the hypothalamus and this is why patients experience disturbances to their eating habits, sex drive and sleeping patterns. Most of the time these aspects are depressed, but there are cases where they become elevated.

Up to seven percent of patients with major depression die from committing suicide. In fact, a study discovered that clinically depressed patients with insomnia and hypersomnia (increased sleep) had higher scores on the SADS suicide questionnaire than those without any sleep disturbances.3 It was also noted that patients with sleep disturbances were much more likely to become suicidal than those without sleep-related problems.

Sleep apnea and mood disorders

Certain sleep-related conditions may also be associated with the development of mood disorders such as major depression.

This includes sleep apnea, which is a condition associated with difficulty in breathing while the affected individual is sleeping. This disturbance in the person’s ability to breathe results in decreased oxygen supply to the body with resulting sleep fragmentation and injury to body tissues.   We have also seen snorers ‘gasp themselves’ awake.  This is an example of sleep fragmentation which prevents people with sleep apnea from achieving deep restorative sleep.

Researchers have discovered that sleep apnea is associated with the development of certain mental health issues, especially major depression.4  This link suggests that patients with mood disorders should be evaluated for sleep apnea.

Management of sleep disorders in major depression

The optimal approach to managing individuals with mood disorders and insomnia is to consider them comorbid disorders and treat them both.  It is quite possible that managing an individual’s depression will improve their insomnia.  Similarly, it is quite possible that managing an individual’s insomnia will help their depression symptoms.  However, the optimal approach is to address both.  The management of sleep disorders in patients with major depression can be performed by treating the cause of the depression, or by managing the symptoms of the sleep disturbances.

The two main methods of treating insomnia (with or without depression) are with cognitive behavioural therapy and with medications.  Similarly, the two main ways to treat depression is with therapy and with medications.  As expected, there can be a lot of overlap.  Therapy for both insomnia and depression is optimally provided by a behavioural medicine provider with expertise in sleep disorders.   This approach attempts to change behaviours and beliefs relative to one’s condition.  It commonly takes many months to achieve but can result in long term symptom relief.

Pharmacologic approaches generally utilize antidepressant, anti-anxiety medications and soporific agents to treat the myriad of symptoms.   Mirtazapine and fluoxetine are two of the former mentioned medications which have been shown to reduce stress and anxiety levels, associated with the development of major depression. Mirtazapine though has been shown to help more than fluoxetine in managing the insomnia associated with depression.5

Benzodiazepines and benzodiazepine-like medications such as zolpidem have been used for many years to help get patients to sleep. These medications don’t treat the sleep disorder, but they do help to sedate the patient so that they can get to sleep.   Over the past decade, there has been a tremendous increase in the number of sleeping pill prescriptions.  Along with that, there has been an increase in the number of night time falls, particularly in the elderly.  Sleeping pills should be utilized at a minimum, with extreme caution and with close oversight by the managing physician.

Some medications that are commonly prescribed for the treatment of depression may however worsen insomnia and impair full recovery from the illness.2 Therefore, caution needs to be exercised when these patients are prescribed medications by their doctors, and that the individual’s unique circumstances are considered when doing so.

Home remedies and natural measures

Alternative therapies such as the use of certain herbs and dietary supplements are noted to be effective in the management of sleep disturbances in the presence of major depression.6 Such products include St. John’s wort and kava to help with the depression caused by anxiety, and valerian for insomnia specifically.

Preliminary evidence from certain studies shows that supplements such as folate, phenylalanine and tryptophan have shown some benefit in improving the effect of conventional antidepressants. Also, omega-3 fatty acids (from fish oil) have shown to have mood stabilizing effects.

It’s important to remember that any natural supplement should be discussed with the patient’s primary care physician to make sure that these products are safe to use, and that they won’t interact with any other medications that may be used by the patient.

Relaxation measures such as deep breathing exercises, aromatherapy, massage therapy, pet therapy, meditation, prayer, yoga and acupuncture are all proven natural measures which can be incorporated to reduce stress and anxiety levels in people.7 Regular aerobic exercise has also been proven to promote a healthy body which also helps with stress relief.  In my personal life, I am certain that daily exercise and meditation as well as aromatherapy and a healthy diet promote my sense of well-being and improve my sleep

Sleep hygiene is suggested to help patients to get to sleep regardless of the cause of the insomnia. These include measures such as going to bed and waking up at the same time every day, following strictly to a pre-bedtime routine, taking a warm bath or shower before retiring to bed, only lying in bed to try to sleep and not watching T.V. or reading a book, and staying in bed even if the patient wakes up during the night.8


Sleep disturbances are very common problems in patients with mood disorders.  Optimal management involves addressing both the mood disorder and the insomnia/sleep condition in parallel utilizing a combinations of behavioural modification/therapy, medications and natural therapies.  One should think of it as a ‘two way street’.  Improving one’s sleep will improve one’s mood problems.  Similarly, improving one’s mood disorder such as depression will commonly improve the quality of sleep.


  1. Peterson, M. J., & Benca, R. M. (2006). Sleep in mood disorders. Psychiatric Clinics29(4), 1009-1032.
  2. Antonina Luca, Maria Luca, & Carmela Calandra (2013). Sleep disorders and depression: brief review of the literature, case report, and nonpharmacologic interventions for depression. Clin Interv Aging, 8, 1033–1039.
  3. Ağargün, M. Y., Kara, H., & Solmaz, M. (1997). Sleep disturbances and suicidal behavior in patients with major depression. The Journal of clinical psychiatry58(6), 249-251.
  4. Sharafkhaneh, A., Giray, N., Richardson, P., Young, T., & Hirshkowitz, M. (2005). Association of psychiatric disorders and sleep apnea in a large cohort. Sleep28(11), 1405-1411.
  5. Winokur, A., DeMartinis 3rd, N. A., McNally, D. P., Gary, E. M., Cormier, J. L., & Gary, K. A. (2003). Comparative effects of mirtazapine and fluoxetine on sleep physiology measures in patients with major depression and insomnia. The Journal of clinical psychiatry64(10), 1224-1229.
  6. Fugh-Berman, A., & Cott, J. M. (1999). Dietary supplements and natural products as psychotherapeutic agents. Psychosomatic Medicine61(5), 712-728.
  7. Arcos-Carmona, I. M., Castro-Sánchez, A. M., Matarán-Peñarrocha, G. A., Gutiérrez-Rubio, A. B., Ramos-González, E., & Moreno-Lorenzo, C. (2011). Effects of aerobic exercise program and relaxation techniques on anxiety, quality of sleep, depression, and quality of life in patients with fibromyalgia: a randomized controlled trial. Medicina clínica137(9), 398-401.
  8. Harvey, A. G. (2000). Sleep hygiene and sleep-onset insomnia. The Journal of nervous and mental disease188(1), 53-55.

Sleep and aging

Sleep changes dramatically over our life spans.  As we know, newborns sleep the majority of the day and napping persists until age 3-4.  Eventually, our sleep consolidates into a single period of sleep lasting 7-8 hours per night.  Elderly individuals seem to be more prone to distressing sleep disruptions.  This blog post reviews the types of sleep issues that commonly occur as we age.

The effect of age on sleep

We have discussed the effects of decreased sleep on the elderly, and now we shall focus on what the effect a person’s age has on sleeping patterns.

A study has shown that elderly people experience a shorter duration of sleep time, decreased sleep efficiency, and increased waking up at night independent of other factors such as chronic conditions and problems such as sleep apnea.8

The study further found that in men, age was independently associated with more Stage 1 and Stage 2 sleep and less Stage 3 to 4 (slow wave sleep) and REM sleep. Older women were found to have more trouble falling asleep, and experienced more issues with waking up during the night and waking up too early.

Lack of sleep and dementia

One of the vital roles of sleep is to allow the brain to activate a specific system that is responsible for cementing long term memories in the brain cortex. Sleeping also helps individuals to retain information and perform better on memory tasks and activities.1

Studies have shown that sleep deprivation may be linked to the development of dementia disorders, such as Alzheimer’s disease, in the elderly.2 The reason behind this may be due to lack of slow-wave sleep causing the build-up of beta-amyloid proteins in the brain, which ultimately affect the mentioned system responsible for memory consolidation. Alzheimer’s disease also worsens patients’ sleep patterns, so a vicious cycle develops where sleep deprivation causes worsening of the disease which worsens the patients’ abilities to sleep.

Lewy body dementia, which is caused by deposits of Lewy body proteins on the nerve cells of the brain, directly causes increased daytime sleepiness due to lack of sleep.3 This seems to occur regardless of other factors such as disease progression and memory fluctuations in these affected individuals. Lewy body dementia is also responsible for rapid eye movement (REM) sleep disorder, which is a condition characterized by flailing of the limbs and acting out while dreaming. The reason for this is because REM sleep causes temporary paralysis of the skeletal muscles of the body, and REM sleep disorder inhibits this paralysis causing the patients’ symptoms.4

The researchers of these studies have collectively requested that further investigations are conducted into the cause and effect of sleep disturbances on dementia-related pathologies, in order to try and discover possible treatments for the conditions.

Sleep duration and inflammation

A recent study was done determining the link between the duration of sleep in the elderly and what effect inflammation has on the mortality of individuals aged between 71 and 76 years of age.5 The fundamental findings made were that short sleep duration (5 or less hours of sleep per night) was associated with an increase in inflammatory markers resulting in elevated mortality levels, and that longer sleep duration was associated with decreased mortality. These findings were made independent of other risk factors such as smoking, obesity, chronic conditions such as hypertension (high blood pressure) and diabetes (uncontrolled high glucose levels), and complications of these factors such as coronary artery disease.

Therefore, shorter sleep duration is regarded as an independent cause of increased mortality, thereby making this aspect just as detrimental to one’s health as the mentioned factors.

Sleep disturbances and depression

A study that was performed on a community of elderly people yielded that these individuals’ disturbed sleeping patterns were linked to them experiencing varying symptoms of depression.6

The sleep-related issues were linked to those who were female, living alone, unmarried and who had a disability. The two year follow up analysis of these elderly individuals showed that half of the participants still experienced sleep disturbances. It was discovered that the best predictors for future depression were elderly people with sleep disturbances and current depression symptoms; and for those who were not initially depressed, it was sleep disturbances alone.

This latter finding suggests that disturbed sleeping patterns are not only a symptom of depression, but rather as a possible predictor of the future development of depression in the elderly.

Sleep disorders and falls in the elderly

Since sleep-related disorders and falls are a common problem in the elderly, researchers decided to look into the possible link between the two problems.

Surveys were conducted which were filled in by elderly people between 65 and 89 years of age, and most of the participants admitted to falling down when getting up at night. The reason for the latter issue was that the individuals were experiencing poor sleep quality.7 Other risk factors for the falls included the use of diuretics, causing the affected participants to get up and visit the bathroom at night, not being able to see properly and bumping into obstacles, and having to use walking aids for pre-existing physical issues.

Improving sleep in the elderly

Due to the abovementioned issues it would seem prudent to promote an adequate amount of sleep, especially in the elderly who are more prone to developing issues such as dementia and who already have an increased risk of mortality.

A study has shown that supplementing with melatonin, a hormone produced by the pineal gland in the brain and which regulates the sleep-wake cycle, helps to promote an adequate amount of sleep in affected individuals.9

Elderly patients who are prone to sleep disorders have been noted to be those who are on chronic medications. These medications can disrupt the production and clearance of melatonin by the body, thus resulting in the sleep-related issues experienced by the affected individual.


The recommendation made by the researchers, in the clinical studies used for this article, is that an adequate amount of sleep of between six to eight hours is achieved by elderly people. Less than 5 hours and more than 9 hours of sleep can have detrimental effects on the physical and psychological well-being of these individuals.


  1. Scullin, M. K. (2013). Sleep, memory, and aging: the link between slow-wave sleep and episodic memory changes from younger to older adults.Psychology and aging,28(1), 105.
  2. Drummond, S. P., & Brown, G. G. (2001). The effects of total sleep deprivation on cerebral responses to cognitive performance.Neuropsychopharmacology, 25, S68-S73.

3. Ferman, T.J., Smith, G.E., Dickson, D.W., Graff-Radford, N.R, Lin, S-C., Wszolek, Z., … & Boeve, B.F. (2014). Abnormal daytime sleepiness in dementia with Lewy bodies compared to Alzheimer’s disease using the Multiple Sleep Latency Test. Alzheimer’s Research & Therapy, 6, 76.

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