Show
Sleep is as essential to our daily needs as food and water. Although we may feel that sleep simply rests our tired bodies, our brain remains active throughout the night. Sleep plays a critical role in brain as well as physical functioning. What Happens When We Sleep?Our internal body clock, called a circadian clock, tells us when we are ready to sleep. There are actually several circadian clocks in the body, found in the brain and other organs. They are triggered by cues such as daylight (we feel alert) and darkness (we feel drowsy). These clocks can also be triggered by artificial bright light or stimulants like caffeine and alcohol that cause us to feel awake even if it is nighttime. There are several phases of sleep our body experiences. They are classified as REM (rapid eye movement) and non-REM sleep. We cycle repeatedly through these phases about 4-6 times throughout the night, and it is not uncommon to wake up briefly between cycles. Non-REM sleep Stage 1. You transition from being awake to a restful state. Stage 2. You are in a light sleep state. Your breathing, heart rate, and muscle movements slow down. Brain activity also slows, and your body temperature drops. Stage 3. You are in a deep sleep state. This stage often occurs early in the sleep cycle immediately following light sleep. Your heart rate and breathing are the slowest during this phase, and you are not easily awakened. Events of the day are processed and stored in your memory. A lack of deep sleep can leave one feeling tired in the morning even if achieving an adequate duration of sleep. REM sleep During REM, your pupils twitch and move quickly from side to side underneath closed eyelids. Brain activity rises as you breathe faster and your heart rate increases. It is the phase of sleep when dreams are most common, and certain nerves signal your limbs to become temporarily paralyzed so you do not act out the dream. REM tends to occur later at night and into early morning. Memory is processed and stored during REM sleep. Dreams occur during the REM sleep stage and may include events or thoughts you experienced recently. Dreams may occur to help process emotions caused by those events. People report dreaming in vivid color as well as in black and white. Sometimes even a wild crazy dream can be forgotten by the time we awaken in the morning. Hormones that Regulate Sleep CyclesThere are various neurotransmitters and hormones released by the brain that send signals to promote sleep or wakefulness. [1] Many of these chemicals are stimulated by light or darkness.
Immediate Effects of Sleep DeprivationAbout one-third of American adults do not get enough sleep each night, according to the Centers for Disease Control and Prevention. [2,3] Short sleep duration in adults is defined as less than 7 hours of sleep in 24 hours. About 40% of adults report unintentionally falling asleep during the day at least once a month, and up to 70 million Americans have chronic sleep problems. Because of the public health burden of poor sleep health, achieving sufficient sleep in children and adults was included as a goal in the Healthy People 2020 goals. [4] Sleep helps to process your thoughts from the day as well as store memories, so a lack of good-quality sleep can lead to difficulty focusing and thinking clearly. You may feel tired, irritable, or anxious during the day. Performance at work or school may suffer. Your reaction time may be slowed, increasing the risk of driving accidents. In children, insufficient sleep can lead to attention and behavior problems or hyperactivity. In the elderly, lack of sleep may decrease focus and attention, leading to a greater risk of falls, bone fractures, and car accidents. There are several reasons people may get insufficient sleep:
Sleep Deficiency and Disease RiskIf you experience continued sleep deprivation, you will develop a condition called sleep deficiency. This is a state in which you cannot make up the many lost hours of sleep. Sleep deficiency increases the risk of obesity, diabetes, cardiovascular disease, depression, and even early death. Obesity
One may think that getting less sleep would mean more activity due to being awake longer and therefore using more calories. However, studies have found either no increase or very small increases in energy expenditure with sleep deprivation, and even a tendency towards reduced physical activity due to fatigue. [9] Less physical activity combined with the increased calorie intake associated with sleep deprivation increases the risk of obesity. Other effects of poor sleep include increased fat storage in the belly area, higher body mass index, poorer quality diet, and decreased insulin sensitivity. [6,10] Interestingly, some studies have also shown that longer sleep times (more than 9 hours) are also associated with developing belly fat compared with sleeping 7-8 hours a night. [7] Diabetes
Some people who have insufficient sleep have a condition called obstructive sleep apnea, which blocks breathing in the upper airway tubes, often because of increased fat in the tongue. Sleep apnea is independently associated with insulin resistance; a lack of oxygen while sleeping can cause oxidative stress and inflammation that are believed to progress toward insulin resistance. [11] Cardiovascular disease Both shorter and longer sleep durations are associated with cardiovascular diseases. [12,13] Proposed reasons include activation of the sympathetic nervous system and impaired endothelial function, which can lead to elevated blood pressure and hardening of arteries. There may also be greater release of pro-inflammatory cells and decreased immune function. Metabolic changes include a disruption in appetite hormones and circadian rhythms that lead to inflammatory conditions. [14]
Depression Poor sleep and insomnia (an inability to sleep or stay asleep) are associated with depression, especially if the insomnia becomes chronic. [20] Insomnia is also associated with increased likelihood of insomnia relapsing over time. Poor sleep quality can impair functioning, increase fatigue, and lead to mood changes. The reverse is also true in which depressive symptoms of intense sadness or hopelessness can interrupt sleep. Insomnia as well as oversleeping are common signs of clinical depression, according to the National Institute of Mental Health. [21] Treating the depression may lead to improvements in sleep quality. If there is an underlying medical disorder causing the insomnia such as obstructive sleep apnea or chronic pain, then treatment should address these first. Dementia In 2021, authors of a cohort study sought to tease out the association of early brain changes and sleep changes by including younger patients 50 years of age. They followed 7,959 participants for up to 25 years and found that participants who were between the ages of 50-70 years and slept 6 hours or less a night showed a 30% higher risk of developing dementia in later life, compared with those who slept 7 hours. [40] The association was only slightly weaker when authors controlled for various factors independently associated with dementia like cardiometabolic status (high blood pressure, diabetes mellitus, body mass index, cardiovascular disease), sociodemographic variables (age, sex, ethnicity, education, marital status), health behaviors (smoking, alcohol, exercise, intake of fruits and vegetables), and mental health factors (depression). The authors did not find an association with longer sleep durations (8 or more hours) and dementia, though this may have been due to the low number of participants who slept longer durations. Mortality Prospective cohort studies have found that both a chronic lack of sleep (less than 7 hours) and long sleep durations (more than 8 hours) are associated with greater risk of death from all causes. [7,13] Obstructive sleep apnea and insomnia are also associated with increased mortality. [22,23] However, long sleep durations appear to be more associated with increased risk of mortality than inadequate sleep. [13] Some studies show that women may have greater risk of mortality related to short sleep durations than men. [24] Longer sleep times are associated with several factors that are associated with mortality, including fatigue, stress, obstructive sleep apnea, and increased inflammation of heart arteries. More research with randomized controlled trials is needed to better understand the reasons for these findings. Medical Conditions that Interfere with Sleep
People who work overnight shifts, early morning shifts, or rotating shifts (both day shifts and night shifts) may develop something called shift work disorder (SWD). Studies show that those with SWD have poorer sleep quality than day workers. [28] They may take longer to fall asleep, experience insomnia, and feel excessive sleepiness while awake. This is caused by attempts to sleep in daylight, which opposes natural circadian rhythms. Poor sleep hygiene further aggravates the problem. SWD is associated with decreased alertness, higher risk of work-related accidents, and increased depression and anxiety. SWD is also associated with metabolic changes increasing the risk of heart disease, obesity, and digestive problems caused by irregular eating habits or poor diet. The following tips can help if you work nontraditional hours: [29]
Sleep Deficiency and Eating BehaviorsEpidemiological studies show that insufficient sleep is independently associated with a higher risk of obesity. Clinical studies of of sleep-restricted adults show an increased hunger and calorie intake when participants are allowed free access to food. [7] A preference for late evening or nighttime food intake and increased snacking has been observed. [9] There also appears to be a food preference for higher carbohydrate and fat foods, which could partly explain the overall higher calorie intake. Changes in hormone levels that signal either hunger or satiety have also been observed in clinical sleep restriction studies. Leptin is a hormone associated with satisfaction. When food enters the stomach, leptin is released from fat cells and travels to the brain where it signals the body to stop eating by creating a sensation of fullness. People with obesity may actually have very high levels of leptin; the more body fat one has, the more leptin is produced in fat cells. However, a condition called leptin resistance may occur in which the brain does not receive the usual signal from leptin to stop eating. In response, more and more leptin is released. Lower leptin levels as well as high leptin levels suggesting leptin resistance have been observed in sleep-deprived adults. [7] Ghrelin, the “hunger hormone,” typically has the opposing action of leptin. It is released in the gut and sends hunger signals to the brain when someone is not eating enough. About three hours after eating a meal, ghrelin levels drop. Clinical studies have found that sleep restriction leads to elevated ghrelin levels. [9] Despite this interesting theory of poor sleep leading to changes in appetite hormone levels, other studies have found no changes and therefore the association is still inconclusive. [9] Conflicting findings may be due to differences in the study participants (e.g., age, gender) and differences in how the researchers defined the duration and severity of sleep restriction. How Much Sleep Do We Need?Sleep needs change as we age, with the average person generally requiring less sleep at older ages. However, specific sleep amounts vary by individual. According to the National Sleep Foundation and American Academy of Sleep Medicine (AASM), newborns need the most sleep, at 14-17 hours a day, followed by infants at 12-16 hours a day including naps. Toddlers need about 10-14 hours a day. Preteens and teenagers need about 8-12 hours a night, and adults about 7-8 hours a day. [30] A consensus by the AASM and Sleep Research Society recommends that adults should sleep 7 or more hours a night to promote optimal health. [31] Despite these general recommendations on sleep duration, individual differences in sleep requirements exist. In most epidemiologic studies, increased risk of adverse health outcomes such as obesity, diabetes, and cardiovascular disease, has been observed among those who reported sleeping 5 hours or less per day, and 9 hours or more per day. Thus, a range of sleep hours (more than 5 and less than 9) is considered appropriate for most healthy adults. Other factors such as quality of sleep are important, because just meeting the total recommended sleep hours may not be enough if one wakes up frequently in the night. A common belief is that lost sleep from a late night out or studying can be recovered by “sleeping in” another day or taking naps. However, both of these methods disrupt the body’s circadian rhythms and may deprive the body of deeper sleep stages. In fact, increased variability in how much sleep we get from night to night is associated with an increased risk of developing metabolic and heart diseases. [32] It is important to respond, whenever possible, to the body’s natural signals of sleepiness. Herbal supplementsTwo popular herbal supplements, melatonin and valerian, are used as sleep aids. Melatonin has been shown to quicken time to sleep and have modest benefits on sleep duration and quality, but can cause daytime drowsiness. It is well tolerated in adults with few reported adverse events in doses up to 10 mg. The American Academy of Sleep Medicine (AASM) recommends the judicious use of melatonin for certain sleep and circadian disorders such as shift work disorder or jet lag. [33] Valerian contains small amounts of GABA, a sleep-promoting neurotransmitter, and some studies have shown that valerian can improve sleep. However, other studies have found no difference in sleep when taking valerian compared with placebo, and there appears to be minimal benefit in those who have diagnosed insomnia. The AASM does not recommend valerian for insomnia disorder. [33] It is important to note that supplements are not reviewed by the U.S. Food and Drug Administration for safety or effectiveness. Therefore doses and preparations of these herbs can vary widely. A study of 31 melatonin products found that the melatonin levels in the pills ranged between 83%-478% of the dose reported on the label. [33] More than 70% of the products varied from the labeled dose by more than 10%. If supplements are used, look for a label verifying its quality from a third-party, such as from the U.S. Pharmacopeia. Sleep medicines Common medicines prescribed for sleep include sedatives such as benzodiazepines (e.g., Valium, Xanax, Klonopin, Ativan*). They help with falling asleep initially, but tend to reduce the amount of deeper sleep. They are not recommended for long-term use because they can worsen insomnia, increase depression, and impair memory, and are associated with increased risk of falls, cancer, and early death. [34] Long-term use of benzodiazepines can promote psychological dependence, and there is a risk of addiction and abuse. [35] Tolerance can also develop over time, requiring larger doses to maintain their effectiveness. Because of these side effects, benzodiazepines are not recommended to treat insomnia in older adults. [35] There are other classes of sleep medications including non-benzodiazepines (e.g., Lunesta, Ambien) and antidepressants (e.g., Zoloft) that also quicken the time to fall asleep but may interfere with deeper sleep stages. Anticholinergic medications (e.g., Benadryl) can increase the risk for cognitive impairment and decline. Generally, sleep medicines are most effective when used occasionally or for a short time of less than one month. The American Academy of Sleep Medicine (AASM) recommends that cognitive behavioral therapy be used as the initial treatment for insomnia. [*The inclusion of brand names is included for reference and does not constitute an endorsement. The Nutrition Source does not endorse any specific brands.] Other therapies Randomized clinical trials have shown that cognitive behavioral therapies (CBT) for sleep such as minimizing napping during the day, relaxation training, breathing exercises, and sleep hygiene are highly effective and recommended as first-line treatments for insomnia. [35,33] They have been found more effective than medications for the long-term management of insomnia. People may be asked to keep a sleep journal to record sleep habits and activities performed around bedtime, which can help determine the most appropriate CBT. Sleep Hygiene Tips
A solid body of research confirms that both aerobic and resistance exercises improve sleep, with reported improvements comparable to the effects of pharmacological treatments for insomnia if exercises are performed regularly. [36] A review of 13 studies found that regular resistance exercises (using resistance bands, strength machines) performed 2-3 times a week for an average of one hour improved sleep quality. [37] It also found that resistance exercises decreased anxiety and depression, which could be a factor in improving sleep. However, it is not recommended to do vigorous exercises such as running or interval training within one hour of bedtime. A review of 23 studies found that healthy adults who performed high-intensity exercise too soon before bed had difficulty falling asleep and experienced poorer sleep quality. [38] Yet, this study and others did not find that performing more moderate exercises or exercising vigorously further away from bedtime caused sleep disturbances, and in fact helped people to experience increased amounts of deeper sleep. [38,39] References
Terms of UseThe contents of this website are for educational purposes and are not intended to offer personal medical advice. You should seek the advice of your physician or other qualified health provider with any questions you may have regarding a medical condition. Never disregard professional medical advice or delay in seeking it because of something you have read on this website. The Nutrition Source does not recommend or endorse any products. |