From Health Facts
Sleep is a natural state of rest for the mind and body. A third of life is spent sleeping, yet it is often taken for granted or abused. Sleep is essential to physical, cognitive and emotional well being. As sleep is perceived as lacking importance in our society, sleep difficulties are rapidly becoming more prevalent. Insomnia is defined as difficulty in initiating or maintaining sleep for an adequate amount of time. It is estimated that 3.3 million Canadians a year, or about 1 in every 7th persons, have trouble going to sleep or staying asleep.
Stages Of Sleep
During the day the brain is firing at a rapid rate – known as beta waves - keeping one alert, allowing one to think and to be aware of their surroundings. Normal sleep is characterized by alternating between light, deeper slow-wave sleep (NREM) and REM sleep. Each sleep cycle is roughly 90 minutes, allowing an individual to move through 4 to 6 cycles in a given night. During the first cycle the least amount of time is spent in REM sleep and the most time in stages 3 and 4 of NREM sleep. Throughout the night, as the cycles continue, there is an increase in the amount of time in REM sleep and a decrease in the amount in NREM. During 7.5 hours of sleep you will spend about 25% in REM sleep.
Rapid eye movement or REM sleep is the period of sleep that the eyes flutter back and forth and vivid dreams are experienced. During this stage the brain is highly active and muscles are temporarily paralyzed. Researchers believe this is to protect an individual from acting out their dreams. This stage is characterized by alpha and beta brain waves, bringing the brain close to a wakeful state. Respiration rate, heart rate and blood pressure all fluctuate during this time in response to dreams. Women may experience clitoral engorgement and men may experience penile erection as part of the autonomic nervous system activation. It is easier to arouse someone from REM sleep than from stage 3 or 4 of NREM sleep.
NREM Stage 1 - Stage 1 of NREM begins when the brain waves slow and one begins to relax. This stage is known as a state of transition when an individual slips into the beginning of sleep. One may notice physical changes as they relax: brain activity decreases, heart rate and blood pressure drop, muscles become relaxed, breathing slows and body temperature drops. This stage is characterized by theta brain waves and lasts for 5 to 10 minutes.
REM Stage 2 - In stage 2 of NREM, the brain waves slow even more. This is still a stage of moderately light sleep and it is fairly easy to arouse someone. However, during this stage the body has committed to sleep rather than just dozing. Healthy adults typically spend about 50% of their time in stage 2.
NREM Stage 3 and 4 - Stages 3 and 4 are often grouped together, because, from a physiological point of view, they are relatively similar. During stages 3 and 4 the senses and mind are completely cut off from the external environment. The brain waves have switched to a delta brain wave activity. If a person were to be aroused from this stage, it would be quite difficult to wake them. If they do wake up, they would awaken feeling groggy and disoriented. Stage 4 is the stage of deepest sleep, followed by stage 3. It is during stage 4 that growth hormone is secreted and the body begins to repair itself. The immune system also works hard during this stage. This is why, when falling ill, a good night’s rest helps one to feel better. On the other hand, when lacking sleep, the body is not awarded the opportunity to repair and is unable to ensure optimal immune function. During sleep deprivation the body craves delta sleep and will do its best to get one to stages 3 and 4 in a hurry. This is noticed when someone falls asleep quickly and it is very difficult to wake them. Their body has pushed them to a deep sleep quickly to make up for a lack of repair processes.
During sleep the body’s energy shifts focus from external activities such as processing information, movement and digestion to internal activities such as self healing, rejuvenation and repair. Some of the internal processes that occur during sleep include:
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- Cellular Repair: The body must constantly keep up with the wear and tear of daily living. When awake the body is in a breakdown process or catabolic process, in which large amounts of adrenaline (the fight or flight hormone), noradrenaline and cortisol (two stress hormones) are released which helps the body deal with daily strains.
- At night, these hormones drop and the body shifts to anabolic processes where it releases growth hormone which stimulates the cellular repair process. Growth hormone initiates protein synthesis, breaks down fats to supply energy for tissue repair, and stimulates cell division to replace old or malfunctioning cells.
- Growth hormone is released in stage 4 of sleep, the deepest stage of sleep. Balancing catabolic and anabolic processes aids cellular repair which is vital for health and well-being. This also explains why it is necessary and common for a person to require more sleep when dealing with acute or chronic illnesses.
- The maximum healing potential is between 11 p.m. and 1 a.m.
- Immune System Replenishing: The immune system works hard to keep us free of illness by attacking anything that it does not recognize as self. The immune system also recognizes if one of the body’s own cells has mutated or become cancerous and attempts to kill it off to keep us healthy. If the immune system recognizes an invader, it releases interleukins (a specific protein) which signal other immune cells to come to the area to multiply and attack. Special proteins called immunoglobins or antibodies are called upon to identify and neutralize foreign bodies. During sleep the body releases large amounts of interleukin 1 and tumor necrosis factor. Interleukin 1 is a powerful immune system messenger that allows the body to mount a fever if necessary and also helps to decreases inflammation.
- Tumour necrosis factor is a potent killer of cancerous cells and rises ten fold in the blood during sleep. Natural killer cells are also affected by sleep. Although no change is noticed during a sleepless night, their number is 30% lower the following night. Natural killer (NK) cells are essential to the body’s defenses. Decrease in NK cells indicates a weakened immune system making one more susceptible to illness. Sleep is of vital importance and assists the body’s ability to fight infections, cancer and inflammation. A chronic state of insomnia increases the risk of disease.
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- Increased longevity. Sleep duration is related to length of life, with a greater risk of death in those sleeping fewer than 6 hours a night. Sleep deprivation is also linked to vehicle crashes and deaths. Insomnia early in adult life is a risk factor for the development of clinical depression and mental health disorders.
- Muscle relaxation: During the night muscles can take a break and relax. Respiratory muscles also relax, resulting in the breathing rate slowing down. During REM sleep, muscles become so relaxed that they actually become temporarily paralyzed, called muscle atonia. This is thought to protect a person from acting out their dreams. Muscle relaxation is a necessary component of sleep in order to allow the body time to recharge and replenish. When muscles are relaxed, there are less metabolites formed, allowing for additional cellular repair and replenishing.
- Weight management: Adequate sleep is required for weight management. Sleep deprivation is linked to weight gain, typically because the amount and quality of sleep affect hormone levels, namely the levels of leptin and ghrelin. Many physiological processes depend on these hormone levels to function properly, including appetite. Leptin is a hormone that affects the feeling of fullness and satisfaction after a meal, and ghrelin is the hormone that stimulates appetite. When you suffer from sleep deprivation, your body’s levels of leptin fall and ghrelin levels increase. This means you end up feeling hungrier without feeling satisfied by what you eat, causing you to eat more and, consequently, gain weight.
- Free radical scavenging: Sleep is the body’s natural antioxidant. Throughout the night large amounts of free radicals are scavenged from the brain and other vital organs, protecting them from oxidative damage. Most individuals can handle a few days of sleep deprivation, but prolonged depletion of sleep creates advanced aging to the brain, neuronal damage and elevated night time cortisol levels.
- Cognitive enhancements: Without adequate rest, the brain’s ability to function quickly deteriorates impacting concentration, consolidation of memories, and the learning of new motor tasks.
- The brain works harder to counteract sleep deprivation effects, but operates less effectively. Sleep helps with memory in two ways; first, when someone is sleep deprived, there is an inability to concentrate and, therefore, an inability to learn efficiently; secondly, in the consolidation of memory. Memory consolidation implies storing short term memories to long term memory. Memory consolidation occurs during sleep through the strengthening of neuronal connections that form memories. Another area of research is on sleep and procedural memory. Procedural memory is the remembering how to do something and REM sleep seems to play a pivotal role in this. Insomnia early in adult life is a risk factor for the development of clinical depression and mental health disorders. 
- Chronic sleep deprivation is linked with cognitive impairments, the decrease of the brain’s ability to problem solve and the impairment of an individual’s ability to perform optimally. Sleep deprivation has been associated with increased accidents and injury. When decision-making abilities are compromised, the brain falls into rigid thought patterns that make it difficult to generate new problem-solving ideas. Insufficient rest can also cause people to have hallucinations.
- Regeneration of personal essence: Adequate deep restful sleep is essential to a person’s overall sense of wellbeing. It allows a person to process and recover from each day and to feel rejuvenated and ready to handle the next. Sleep is tied to a person’s overall vitality and to their sense of inner strength and ability to heal. Lack of adequate restful sleep is associated with increased aging and with greater dissatisfaction in life. Sleep duration is related to length of life, with a greater risk of death in those sleeping fewer than 6 hours a night.
How Much Sleep Is Optimal?
When it comes to the amount of sleep needed for each person, there is tremendous variability among age groups but also among members of the same age population. The Canadian National Sleep foundation recommends 7 to 9 hours for adults. See the chart below for sleep recommendations for each age group. Please visit 
- Newborns (0 – 2 months)need 12 - 18 hours
- Infants (3 to 11 months)need 14 - 15 hours
- Toddlers (1 – 3 years)need 12 - 14 hours
- Preschoolers (3 – 5 years)need 11 - 13 hours
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- School-age children (5 – 10 years)need 10 -11 hours
- Teens (10 – 17 years)8.5 - 9.25 hours
- Adults need 7 - 9 hours
There are numerous internal and external factors that can promote sound restful sleep or can wake an individual leaving them lethargic, irritable and moody due to sleep deprivation. The most common factors that disturb sleep include:
- Mental Unrest is the most common cause of a disruption in sleep.
- Most individuals with an active mind find it difficult to fall asleep or find themselves waking between 3 and 5 am.
- Both short term and long term stress and anxiety can cause significant impairments in an individual’s ability to fall asleep. Stress and anxiety cause increased muscular tension and sympathetic nervous system activation. In addition to these negative emotional states impairing sleep, sleep deprivation increases an individual’s level of stress and anxiety. Individuals become anxious and stressed about not sleeping creating a vicious cycle.
- Anticipatory anxiety is anxiety that interferes with sleep. This is anxiety experienced the night before a significant event or a stressful period in life causing an overactive mind which in turn affects sleep ability.
- Depression and feeling down or confused are also linked with insomnia. Working on figuring out and addressing what is really bothering you is often the best solution.
- Food choices that you make greatly influence sleep.
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- Root vegetables are high in minerals and are more grounding and settling to the body helping promote restful sleep.
- Tryptophan, an essential amino acid found in turkey, milk, miso soup, eggs, nuts, figs, fish, bananas, dates and papaya, helps the body to produce serotonin, a neurotransmitter that helps promote relaxation and sleep.
- Complex carbohydrates and starches promote sleep as they release sugars into the blood causing a compensatory release of insulin followed by a drop in blood sugars causing the body to feel fatigued. Eating a high-carbohydrate meal (potatoes, pasta and whole grain breads) three or so hours before bed is often helpful for those that have trouble falling asleep.
- Lettuce can often promote healthy sleep as it contains an opium-related substance combined with traces of the anticramping agent, hyoscyarnin. Include lettuce as part of your evening meal.
- Include foods high in Vitamin B3 (niacin) such as legumes, peanuts, nutritional yeast, fish or poultry. Niacin is involved in serotonin synthesis and promotes healthy sleep.
- A glass of warm milk with honey is one of the oldest and best remedies. Milk contains tryptophan which, when converted to serotonin, induces sleep and prevents waking.
- On the contrary, certain foods can negatively impact sleep.
- As most individuals know, caffeine is a nervous system stimulant. Some individuals are so sensitive that even a cup of coffee in the morning or chocolate bar can cause a sleepless night. Avoid foods high in caffeine such as coffee, tea, cola and chocolate.
- Sugar stimulates the nervous system and hence, sugary desserts and for some even the consumption of fruit after dinner is best avoided if you desire a good night’s sleep. Sugar causes a rapid increase in blood sugar which calls upon the pancreas to release insulin. Once insulin is released, sugar enters the cell and blood sugar rapidly drops. If sugar is ingested right before bed, a drop in blood sugar occurs in the night calling upon the adrenal glands to release hormones to restore blood sugar balance. This release of hormones wakes you up and affects the normal sleep patterns.
- Foods high in tyramine increase the release of norepinephrine, a brain stimulant.If you have difficulty sleeping, avoid bacon, cheese, chocolate, eggplant, ham, sauerkraut, sugar, sausage, spinach, tomatoes and wine close to bedtime.
- Alcohol, another nervous system stimulant, interferes with the natural sleep cycles and also increases anxiety levels interfering with sleep. Alcohol impairs the transport of tryptophan into the brain and hence, disrupts serotonin levels.
- Any food that you are intolerant to is best avoided. Food intolerances are often the cause of snoring and can contribute to gas, heartburn, indigestion, pain and discomfort.
- Diets high in meat or other proteins can inhibit sleep by blocking the synthesis of serotonin, making you feel more alert. Diets high in protein are also more acidic and take longer to digest.
- Avoid too many ingredients in a meal and too much food late at night.
- Dietary Regimen. Ensuring that your last meal of the day is about 3 hours before bedtime is important because:
- It ensures that your blood sugar is not spiking in the middle of the night, thus waking you up.
- It allows the body time to complete digestion so that when you are sleeping your body can focus on healing and repairing. It minimizes any discomfort that may be associated with going to bed with a full stomach.
- During digestion your metabolic rate and body temperature increase. This increase in body temperature can throw off the internal stimulus for inducing sleep.
- Smoking Individuals who smoke require more time to fall asleep, have less oxygen absorption, more congestion and snoring and less deep sleep. Another good reason to quit smoking!
- Physical Activity People who regularly engage in exercise have fewer episodes of sleeplessness and typically fall asleep more easily and sleep more deeply and soundly.
- Exercise promotes improved sleep quality by allowing for smoother and more regular transitions between the cycles and phases of sleep.
- Increased physical activity is also associated with improved mood and well-being. Individuals who exercise appear to have better emotional balance, decreased anxiety and depression, thus promoting restful sleep.
- The change in body temperature promoted by exercise triggers areas in the brain that help to initiate sleep.
- When exercising, the body releases endorphins, a natural opioid in the brain, that increase feelings of wellbeing and decrease the sensation of pain. These endorphins are a nervous system stimulant and if one exercises too late in the evening, it impairs your ability to fall asleep.
Initiation of an exercise regime can, however, temporarily impair sleep.
- Muscle stiffness and soreness experienced after initiation of a new exercise routine can cause the body to experience pain, therefore, interfering with sleep.
- Too much physical activity or physical activity at the wrong time can also interfere with sleep. Do any aerobic or strenuous exercise in the morning or afternoon, not close to bedtime if experiencing sleep difficulties. Choosing to take a leisurely walk or to do some gentle yoga or stretching is a good way to unwind at the end of the day and will support your body winding down and preparing for sleep.
- Sleep Regimen When you choose to sleep affects health. Sleep comes most easily and is the most conducive to health when it is in line with the natural circadian rhythms. Circadian rhythms govern the body’s hormonal, physiological and behavioural processes. The most notable circadian rhythm is the sleep cycle.
- Establishing a regular sleep schedule and sleeping when it is dark and waking when it is light ensures balances between the delicate systems of the body. Not being in sync with the circadian rhythm can lead to hormone imbalance, seasonal affective disorder and jet lag just to name a few.
- Melatonin is the second most powerful message for the body’s circadian rhythm. Melatonin is a hormone secreted by the pineal gland which is located in the center of the brain between the two hemispheres. Melatonin is the “hormone of darkness”, as its levels rise in response to darkness and fall in response to sunlight. Its secretion begins in the evening as the sun is setting and signals the body to feel tired and go to bed. Melatonin production deceases throughout the night and reaches a low in the morning when one is cued to wake up. Exposure to increase in light in the evening or while sleeping can disrupt melatonin levels and often contributes to sleep disorders.
- Cortisol is known as the stress or the 'awake hormone. It is responsible for waking a person up. On a normal basis its release follows the circadian rhythm with a peak in cortisol naturally occurring between 6 and 8 a.m. The initiation of sleep is associated with low levels of cortisol. Many sleep problems, such as night time awakening and difficulty following asleep are linked with increased cortisol levels and are associated with chronic stress or adrenal fatigue.
- Body temperature is also governed by the circadian rhythm. Body temperature and sleep run independently, yet they are usually synchronized. Body temperature fluctuates throughout the day, rising in the morning making one alert and falling during the night. It is easiest to sleep when body temperature is reaching its lowest temperatures. Around 6 to 8pm body temperature reaches a peak and begins it decline, at the same time melatonin begins to rise making one feel sleepy.ii Temperature reaches its lowest point between 3 to 5 a.m.
- Sleep Environment In order to sleep soundly it is important to have a sleep environment that is quiet, dark, secure and comfortable.
- Loud noise causes excess nervous system stimulation and inhibits the ability to sleep or to wake an individual from a sound sleep.
- Light entering the bedroom, either from the outdoors or from an alarm clock, impacts the release of melatonin from the pineal gland affecting hormone balance, causing a direct impact on the ability to fall asleep. Choose to sleep in a completely dark and quiet room.
- Temperature also plays a role in your ability to sleep soundly. At night the body temperature drops, cueing us to feel tired and to go to bed.
- In order to have a comfortable and uninterrupted sleep it is important to have enough covering on the bed to not cause one to wake feeling chilled.
- Having a comfortable mattress and a bedroom that is comfortable and free of stressors (i.e. computer, work, etc.) will help ensure a good night’s rest.
- Reserve the bedroom for sleep and sexual activity. Watching television, reading or doing computer work can create a stimulating environment and impact the ability of the mind to equate going to bed with sleeping.
- Physical Ailments There are a number of physical ailments that contribute to insomnia or that aggravate it. Ailments that result in frequent waking to use the washroom, pain and discomfort, changes in sweating or temperature and other symptoms can cause disturbances in sleep throughout the night.
Inadequate sleep can be both a cause of other diseases and conditions or it can be a result of other underlying conditions. The following conditions are associated with sleeping problems and insomnia:
- Mental unrest: Stress and anxiety are the most common cause of a restless night.
- Pain Individuals who suffer from chronic pain typically complain of sleep disturbances. Fibromyalgia is associated with a great deal of sleep disturbances; as are musculoskeletal pain, especially low back pain, TMJ pain and arthritis.
- Sleep disturbances also seem to decrease a person’s pain threshold, further impairing one’s ability to sleep.
- Menopausal insomnia A significant percentage of women will suffer sleep disturbances either due to hot flashes or anxiety during menopause.
- Adrenal Dysfunction: The adrenal glands are responsible for release of cortisol and epinephrine (the fight or flight hormone). Individuals with adrenal dysregulation have irregular cortisol levels which contribute to sleep problems.
- Dysglycemia. Improper sugar regulation disrupts quality of sleep.
- Sleep disturbances independently increase an individual’s risk of insulin resistance and other components of metabolic syndrome.
The opposite may also be true, in that metabolic abnormalities may contribue to sleep disturbances.
- Heartburn: When circadian rhythms are disrupted, stomach acid and digestive enzyme secretion become altered. This leads to oesophageal irritation and reflux. Conversely, gastroesophageal reflux disease or heartburn in itself can cause insomnia. If an individual cannot lie down horizontally due to the presence of stomach acid irritating the oesophagus, sleep will be greatly impaired.
- Cardiovascular Disease (CVD): Individuals with poor sleep habits are unable to enter into stage 4 of sleep, which is pivotal for the function of our immune system and the natural anti-inflammatory properties supported by this sleep stage. In epidemiological studies, individuals who suffered from sleep deprivation had increased C-reactive proteins in the blood. C-reactive protein is a marker of inflammation and is associated with an increased risk of cardiovascular morbidity. Increased systolic blood pressure and heart rate were noted in individuals with poor sleep habits.
- Sleep Apnea: Untreated, obstructive sleep apnea has been associated with cardiovascular disease, insulin resistance, gastroesophageal reflux disease, motor vehicle accidents and decreased attention and working memory - conditions all caused by inadequate sleep.
- Restless leg syndrome this sensation always occurs during times of rest or inactivity, directly impacting an individual’s ability to sleep.
- Obesity: Sleep deprivation has been associated with alteration in energy balance within the body. Maintaining adequate energy balance is imperative to maintain a constant weight. Excess energy intake and decreased energy expenditure often results in weight gain. Sleep deprivation has been associated with alterations in appetite regulation.
- When individuals are sleep deprived there is a decrease of the hormone leptin. Leptin is responsible for our appetite regulation. It is stored in our adipose tissue and is up-regulated when we are full. Sleep deprivation decreases leptin production and as a result the body does not get a signal that it is full. In addition to changes in leptin levels, it was observed that ghrelin levels were also altered in sleep deprivation. Ghrelin signals the body when it is hungry. Normally its levels increase when the stomach is empty and decreases once you are full. However, in sleep deprivation, ghrelin levels remained elevated despite adequate food intake. Therefore, sleep deprivation seems to play an important role in appetite and food intake and can directly predispose someone to obesity.
- Jet Lag For some individuals travelling to an area with a different time zone causes them to feel groggy, irritable, fatigued, disorientated and greatly affects their sleeping patterns. This feeling is called jet lag and is due to a disruption in circadian rhythms. (see section on circadian rhythms for more information.)
From a naturopathic perspective assessing sleep is primarly determined through a detailed interview process and may involve keping a sleep diary. Questions relating to sleep quality, quantity and energy will all contribute to an accurate diagnosis why someone is having sleeping difficulties. In order to find success in treatment it is imperative to find the root cause of the sleeping difficulties. Once a thorough assessment of sleep is conducted and identification of the root cause is established, a personalized naturopathic plan will be devised that can help an indiviudal find deep restful sleep.
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There are a number of different ways to address insomnia. The success of any specific treatment option depends on the degree to which it addresses the underlying factors that are impacting sleep. For example, if your insomnia is due to pain, you will probably find minimal relief in taking a supplement that treats insomnia due to anxiety. It is recommended that you work with your naturopathic doctor to understand exactly what treatments are suited for you. The treatments that have been found to be effective include calming teas, meditation, journaling, deep breathing, various supplements, botanical medicine, homeopathy, acupuncture and many forms of body work.
- ↑ Canada S (Nov 2005) Study: Insomnia. Retrieved June 14, 2010, from statistics Canada 
- ↑ 2.0 2.1 Harvey, J. R. (2001). Deep Sleep complete rest for health, vitality and longevity. New York: M. Evans and company Inc.
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- ↑ Dinarello CA (2009) Immunological and Inflammatory Functions of the Interleukin-1 Family. Annual Review of Immunology;27:519-551.
- ↑ Bouchez C (2007) The Dream Diet: Losing Weight While You Sleep. WebMD website: http://www.webmd.com/solutions/sc/link-sleep-weight-loss/sleep-to-get-thin.
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- ↑ National Sleep Foundation. Sleep Facts and Stats: Healthy Sleep Tips. http://www.sleepfoundation.org/ Accessed July 2010.
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- ↑ http://www.sleepfoundation.org/article/how-sleep-works/how-much-sleep-do-we-really-need
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- ↑ Physical activity promotes sleep. (2005). Retrieved June 18, 2010, from Canadian Fitness and Reseach Institute: http://www.cflri.ca/eng/lifestyle/1996/promotes_sleep.php
- ↑ Atkinson, G. &. (2007). Relationships between sleep, physical activity and human health. Physiology and Behaviour , 90 (2-3), 229-235.
- ↑ Dement, W. (1999). The promise of Sleep. New York: Delacorte Press
- ↑ Quraishi, S (2000) Circadian Rhythms and Sleep. Retrieved June 14, 2010, from serendip: Circadian Rhythms and Sleep
- ↑ 17.0 17.1 Schenck, C. H. (2007). Sleep the mysteries, the problems, and the solutions. New York: Avery
- ↑ Wilson BW, Chess EK, Anderson LE. 60-Hz electric-field effects on pineal melatonin rhythms: time course for onset and recovery. Bioelectromagnetics. 1986;7(2):239-42
- ↑ National Sleep Foundation. 2006 Sleep in America Poll. Washington, DC: National Sleep Foundation;2006
- ↑ Cain N, Gradisar M. Electronic media use and sleep in school-aged children and adolescents: A review. Elsevier. Sleep Medicine. 11(2010)735-742
- ↑ Chaput JP1, Leduc G, Boyer C, Bélanger P, LeBlanc AG, Borghese MM, Tremblay MS. Electronic screens in children's bedrooms and adiposity, physical activity and sleep: do the number and type of electronic devices matter? Can J Public Health. 2014 Jul 11;105(4):e273-9.
- ↑ Drewes A (1999) Pain and sleep disturbances with special reference to fibromyalgia and rheumatoid arthritis. Rheumatology;38:1035-1038.
- ↑ 23.0 23.1 23.2 Lundberg U (2008) Sleep and musculoskeletal pain. International Journal of Behavioral Medicine, 15, 253.
- ↑ Stansbury, J (Mar 2010) Herbal Treatment Approaches to Insomnia. NDNR;:19-21.
- ↑ 25.0 25.1 Miller E (May 2005) Insomnia and Cardiovascular Morbidity. Retrieved June 14, 2010, from MedScape CME: http://cme.medscape.com/viewarticle/505194
- ↑ Ishman SW (2010) Flint: Cummings Otolaryngology: Head & Neck Surgery, 5th ed. Philadelphia: Mosby Elsevier
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