Presentation and course
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• Persons affected by insufficient sleep syndrome report daytime sleepiness or behavioral abnormalities attributed to the sleepiness. These interfere with their activities and functioning. |
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• Other symptoms commonly associated with insufficient sleep include lack of energy, muscle weakness, muscle pain, gastrointestinal disturbances, headache, and difficulties with concentration and attention. |
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• Various functions of the body are affected. |
Insufficient sleep syndrome affects all ages and both sexes.
Patients with sleep insufficiency often report daytime sleepiness that interferes with their activities and functioning. For example, patients with insufficient sleep may inadvertently fall asleep during sedentary activities, such as meetings, reading, watching television or movies, or while driving. Insufficient sleep is associated with an increased risk for motor vehicle accidents by affecting visual search patterns and response times to hazards (46).
The sleep history suggests insufficient sleep by the disparity in reported amount of sleep, often 2 hours or more, when the patient is given the opportunity to sleep ad lib (ie, on a holiday). The excessive daytime sleepiness may become more pronounced in the late afternoon and early evening. Sleepiness usually improves during vacations or holidays. Other symptoms include lack of energy, fatigue, muscle weakness, muscle pain, gastrointestinal disturbances, dry mouth, headache, blurred vision, difficulties with concentration and attention, reduced motivation, irritability, and dysphoria. Any of these symptoms may become the primary focus of the patient and obscure the excessive daytime sleepiness. Importantly, functional and cognitive impairment due to chronic sleep deprivation is often unrecognized by the sufferer.
Prognosis and complications
Complications of insufficient sleep may involve all systems of the body, and important sequelae are listed in Table 1. Recovery from short-term sleep deprivation may occur by restoration of adequate sleep, but long-term sleep deprivation may result in permanent sequelae.
Table 1. Consequences of Insufficient Sleep
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• Daytime sleepiness • Anxiety and depression • Neurocognitive |
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-- Cognitive impairment -- Memory disorders |
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• Neurologic consequences |
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-- Reduction of cells in the dentate gyrus of the hippocampus -- Structural changes in the cortical neurons -- Degeneration of locus ceruleus neurons |
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-- Activation of interictal EEG and precipitation of seizures in epileptic subjects (40) |
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--Increased accumulation of beta amyloid proteins, even in 1 day of sleep deprivation |
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• Metabolic consequences |
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-- Weight gain during insufficient sleep reverses when normal sleep is resumed -- Decrease of appetite-suppressing hormone leptin whereas levels of ghrelin, a hunger promoter, increase spurring a greater desire for food |
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-- Glucose tolerance test shows a prediabetic state in otherwise normal persons -- Increased insulin resistance in diabetes |
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• Cardiovascular |
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-- Atherosclerosis -- Coronary heart disease -- Increased risk of hypertension |
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• Immunological |
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-- Response to vaccine |
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-- Reaction to infection |
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• Reproductive system |
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-- Impairment of sperm health |
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• Genes linked with immune and inflammatory processes: up- or downregulation • Effects related to disruption of circadian rhythms and insufficient sleep --Increased risk of cancer |
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• Disturbance of thermal homeostasis -- Susceptibility to cold- and heat-related illnesses |
Sleepiness associated with insufficient sleep syndrome persists and may get worse without a change in sleep habits. Excessive sleepiness places the subject at increased risk of automobile and industrial accidents, declining job performance, and disrupted social relationships. Sleep deprivation in physicians adversely affects patient care. Impairment of driving abilities due to sleep deprivation is comparable to driving when intoxicated with alcohol and is further exacerbated with concurrent alcohol use. There also are risks associated with excessive caffeine intake or stimulant use that often occurs in patients with insufficient sleep syndrome. Other complications of sleep deprivation include headaches, impaired cognitive functions including language tasks, serial subtraction, memory, attention, and decision making.
In children and adolescents, inadequate sleep impairs attention and concentration and negatively impacts academic performance (11).
A new field of research on bedtime procrastination illuminates a multifaceted phenomenon deeply entrenched in the fabric of modern society. It is defined as the volitional delay of going to bed, without any cause for the delay, resulting in insufficient sleep (20) and has been found to be associated with a myriad of variables, ranging from work obligations to the rigors of parenthood. Studies have demonstrated deficits in self-control and attentional impulsivity. Notably, the insidious allure of smartphone addiction emerges as a potent modulator, exerting its sway over procrastinatory tendencies (16).
Furthermore, psychological stress contributed to further smartphone addiction during the COVID-19 pandemic. In a study by Ma and colleagues, bedtime procrastination predicted the severity of poor sleep quality in children (30).
Anxiety and depression. Chronic insufficient sleep usually results in a more negative mood, with reduced optimism and sociability. Sleep is a potential biomarker for suicidal behavior. A systematic review of literature has revealed a significant association between sleep disturbances and risk of suicide with significant contribution from sleep deprivation-induced neurocognitive deficits, emotional dysregulation, and negative feelings, among other factors (43).
Chronic sleep deprivation is associated with elevated cortisol and decreased testosterone levels. Testosterone is known to enhance the function of the gamma-aminobutyric acid and serotonin systems in the brain. This reduced function provides one possible causal link between two of the most commonly associated psychiatric disorders, depression, and anxiety.
Impairment of brain function. The effects of sleep deprivation on neurocognitive abilities are complex and have been the subject of many studies over the past decade. There is an increasing body of evidence that cognitive complications of sleep deprivation are numerous and are a result of negative effects on the prefrontal cortex and posterior parietal systems. In addition to prefrontal cortex dysfunction, various brain regions involved in verbal working memory have been evaluated and demonstrated vulnerability in the context of sleep deprivation.
Structural changes in human hippocampal subfields resulting from sleep deprivation play a role in determining vulnerability to impairment of memory and are also associated with the quality of NREM slow-wave oscillations during recovery sleep; they also play a role in determining the extent of memory restoration (41). These findings may serve as a predictive biomarker of susceptibility to memory impairment and recovery from sleep deprivation in professions where memory function is critical and insufficient sleep is prevalent. A double-blind, placebo-controlled randomized study to determine the impact of sleep restriction (reduction of 1 hour of habitual sleep duration) on cognitive performance showed impairment of a test of working memory but no effect on tests of sustained attention or decision making (42). Sleep deprivation causes impairment of cognitive flexibility, ie, feedback is less effective in driving behavior modification under changing circumstances (22).
Sleep deprivation may affect the performance in professions requiring intact cognitive function. There has been considerable concern about the performance of overworked and sleep-deprived residents in university hospitals. A study has shown that sleep-deprived surgeons' technical skills are between 11.9% and 32% negatively impacted in a standardized simulated environment, which is likely to have clinical implications for patient safety (50).
Structural and biochemical changes in the brain. Several experimental studies in rats have shown that sleep deprivation causes structural changes in the central nervous system. Sleep-deprived basal forebrain—one of the brain’s main wakefulness centers—experiences an increased release of nitric oxide leading to a buildup of adenosine, a nucleoside that can also affect neural function. Sleep deprivation increases heat shock protein expression in mice. In experiments on mice, extended wakefulness results in reduced sirtuin type 3 (SirT3) activity and, ultimately, degeneration of locus ceruleus neurons (51). Prolonged wakefulness is a metabolic stressor to locus ceruleus neurons leading to failure of adaptive mitochondrial metabolic responses mediated by SirT3, which coordinates mitochondrial energy production and redox homeostasis.
Animal studies have indicated that sleep is essential for maintenance of integrity of cell membranes and myelin in the brain, which are susceptible to sleep deprivation. A diffusion tensor imaging study of normal human volunteers showed that sleep deprivation was associated with widespread decreases in fractional anisotropy that indicate reductions in axial diffusivity, mainly including bilateral frontotemporal and parieto-occipital white matter, the corpus callosum, the thalamus, and the brain stem (14). The findings of this study are consistent with the view that microstructural changes occur in the white matter of the adult human brain over hours to days of sleep deprivation. Permeability of the blood-brain barrier is increased in rats subjected to sleep loss of long duration and is restored following sleep recovery. An ultrastructural study in rats has shown that chronic sleep loss disrupts interendothelial junctions that leads to blood-brain barrier hyperpermeability in the hippocampus (23). The authors of the study suggest that this is because expression of claudin-5, which regulates blood-brain barrier permeability by modifying brain microvascular endothelial cells, is decreased after chronic sleep loss as compared to intact animals.
Diffusion tensor imaging has been applied to the study of diseases characterized by cognitive instability, which is amplified by sleep deprivation and measured by number of lapses on the psychomotor vigilance test (52). There was a considerable inter-individual variation of cognitive instability in response to sleep deprivation, which was associated with differences in white matter integrity.
Cardiovascular effects. Research in the cardiac effects of sleep deprivation has shown that both acute total and short-term partial sleep deprivation results in elevated high-sensitivity C-reactive protein concentrations, a biomarker of inflammation that has been shown to be predictive of cardiovascular morbidity. A review of clinical trials has shown that sleep deprivation can induce autonomic nervous dysfunction, hypertension, arrhythmia, oxidative stress, endothelial dysfunction, inflammation, and metabolic disorder in patients with coronary heart disease (39). Furthermore, sleep insufficiency positively associates with systolic blood pressure or diastolic blood pressure fluctuations (01).
Effects on the reproductive system. Results of a randomized study on Chinese men showed that sleep deprivation with late bedtime was associated with impaired sperm health in the study cohort, partly through increase of antisperm antibody production in the semen (29).
Metabolic syndrome. Several epidemiologic studies show an association between sleep duration of less than 6 hours nightly and obesity and diabetes. Sleep restriction decreases glucose tolerance and insulin sensitivity without adequate compensation in beta cell function. Sleep deprivation has also been shown to reduce leptin and increase ghrelin levels, hormones that increase hunger and appetite (26). Even a relatively brief period of mild sleep deprivation (one and half hours of sleep loss per night over 3 weeks) can lead to changes in insulin sensitivity and body weight (38). Furthermore, sleep deprivation may alter the content of the foods we choose to eat. In a study, 11 subjects increased their consumption of calories from snacks, choosing foods with higher carbohydrate content when sleep deprived to 5.5 hours nightly, as compared to when sleeping 8.5 hours per night (33). A small study looking at cerebral functional MRI showed that subjects who were sleep deprived to 5 hours had a greater increase in brain activity in areas associated with reward when exposed to food stimuli as compared to when they were well rested (45).
Immune system, inflammation, and infection. Systemic infections have been induced in animal models by sleep deprivation. The impact of sleep deprivation on the immune response in humans has been shown to have important consequences. Sleep deprivation has been shown to decrease antibody production following influenza vaccination. In a small study, sleep deprivation dampened the normal circadian T-cell function and regulation, which occurs over a 24-hour period (08). A prospective observational study involving over 50,000 nurses showed that sleeping less than 5 hours per night was associated with a 1.39 relative risk of developing pneumonia (35).
Genetic factors in susceptibility to effects of sleep deprivation. Although sleep duration can be influenced by environmental factors and chronotype, human familial sleep disorders indicate that there is a strong genetic modulation of sleep. Studies on identical and fraternal twins have shown that resiliency and vulnerability to sleep loss are highly heritable (27). There is an ongoing search for genes related to vulnerability phenotype, but none has been identified that can explain the different responses to sleep deprivation. Individual differences in energy balance responses to sleep restriction indicate these responses are phenotypic, with behavioral, physiological, and genetic differences underlying these responses. High-density genome-wide association studies for sleep duration in European populations have identified an intronic variant in the ABCC9 gene that explains approximately 5% of the variation in sleep duration (02). ABCC9 encodes an ATP-sensitive potassium channel subunit (SUR2), which serves as a sensor of intracellular energy metabolism.
Identification of biomarkers, including genetic polymorphisms related to orexin signaling, are important for predicting an individual’s vulnerability to overeating and gaining weight when sleep deprived as they will be an important factor in the management of these problems (44).
Sleep deprivation and the epigenome. Although neuronal effects of sleep deprivation start at the DNA and RNA level resulting in dysregulation of cognitive functions, the epigenome plays an important role in regulating gene expression in this context (15). One example is that sleep deprivation disrupts the cyclic adenosine 3′,5′-monophosphate (cAMP) pathway and CREB (cAMP response element-binding) protein, which mediates histone deacetylase inhibitors, a common epigenetic mechanism.
Effect of insufficient sleep on circadian rhythms. Sleep homeostasis, circadian rhythmicity, and metabolism are interrelated. In mice, sleep restriction leads to approximately an 80% reduction in circadian transcripts in the brain and severe disruption of the liver transcriptome, whereas in humans, sleep restriction leads to a 1.9% reduction in circadian transcripts in whole blood (05). Despite significant reduction in the circadian regulation of transcription in peripheral tissues, rhythms within the suprachiasmatic nucleus are not disrupted. Molecular pathways associated with these disruptions point to molecular mechanisms underlying established adverse effects of sleep deprivation.
Increased risk of cancer due to disruption of circadian rhythms and insufficient sleep. Epidemiologic studies suggest increased risk for breast cancer in night- and rotating-shift female workers, which may be due to several interconnected mechanisms resulting from shift work, such as suppression of melatonin by exposure to light at night, impairment of the immune system due to sleep-deprivation, and metabolic changes with generation of proinflammatory reactive oxygen species (18). This topic, however, is controversial. A large prospective study in Sweden found no association between insufficient sleep and risk of prostate cancer (31).
Disturbance of thermal homeostasis. Short-term, ie, less than or equal to four nights, sleep deprivation can disturb thermal homeostasis, which affects autonomic and behavioral thermoeffectors during acute exposure to low and high ambient temperatures (25). This may be a predisposing factor for the development of thermal injuries.
Sleep deprivation and neurologic disorders. The MedLink article on insomnia describes sleep disorders that occur in various neurologic disorders. The impact of sleep deprivation in several neurologic disorders has been reviewed (07). Important findings are summarized in a Table 2.
Table 2. Effect of Sleep Deprivation on Neurologic Disorders Disease
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Neurologic disorders disease |
Role of sleep deprivation (SD) |
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Alzheimer disease (AD) |
Sleep deprivation increases neuronal firing, upregulates BACE1 proteins, and aggravates neuroinflammation and oxidative stress in Alzheimer disease.
Sleep deprivation-induced impairment of clearance of toxins through glymphatic pathway leads to the accumulation of amyloid beta and tau proteins.
Sleep deprivation has a negative impact on the cholinergic neurons with cognitive dysfunction and impaired memory. |
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Parkinson disease (PD) |
Sleep deprivation causes downregulation of D2/D3 receptors through decreased wakefulness and other altered behavioral effects, which are mediated through the dopaminergic system and result in Parkinson disease-like symptoms.
Sleep deprivation-induced impairment of clearance of toxins through glymphatic pathway leads to the accumulation of alpha-synuclein. |
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Huntington disease |
Sleep deprivation disturbs balanced discharge and firing of basal ganglia, which require appropriate REM sleep and wakefulness.
Sleep deprivation adversely affects the cerebellar and basal ganglia loops, which may in turn lead to pathogenesis of Huntington disease. |
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Multiple sclerosis |
Disruption of circadian rhythm by sleep deprivation leads to the release of cellular and molecular inflammatory mediators, which cause neuroimmune dysregulation.
Sleep deprivation affects the expression of genes involved in the synthesis and maintenance of the myelin proteins. |
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Stroke |
Sleep deprivation aggravates pathophysiology of stroke by increasing the expression of growth-inhibiting genes, neuroinflammation, and oxidative stress.
Sleep deprivation following cerebral ischemia increases the levels of growth-inhibiting gene Neurocan, which forms a barrier and inhibits neuronal reconnection and recovery by neuroplasticity. |
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Epilepsy |
Sleep deprivation initiates epileptic seizures and facilitates epileptiform discharges. |
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Autism spectrum disorders (ASD) |
Sleep deprivation is associated with an increase in the severity of autism scores and affects the daily functioning of autism spectrum disorder patients. |
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Neuropathic pain |
In animal experimental studies, sleep deprivation following chronic constriction injury increases microglial activation in the cuneate nucleus and aggravates neuropathic pain induced by nerve injury. |
Clinical vignette
A 27-year-old, right-handed woman presented to the sleep center outpatient clinic for initial evaluation of her longstanding excessive daytime sleepiness. For the past 7 years, the patient had been excessively sleepy during the day, falling asleep in sedentary situations. Specifically, she reported falling asleep when grading her students’ papers (she used to fall asleep in class when she was a student herself), in traffic at red lights, when talking to people, and when watching television. She stated that her sleepiness worsened after she began working two jobs several years ago. On weekdays, she usually went to bed around 11:30 PM to midnight and got up at 5:30 AM, sleeping a solid 5.5 hours. On weekends, she usually went to bed around 4 AM and slept until noon or 1 PM. When she slept in longer, she felt more refreshed, but was still sleepy and tended to fall asleep, although less frequently, during sedentary situations. She did not take any scheduled naps. She rarely drank caffeinated beverages. She drank alcohol every other weekend. She denied smoking or using recreational drugs. She denied snoring, gasping for air, choking spells, or being told she stops breathing when asleep. She denied cataplexy or hypnagogic hallucinations. On occasion, however, she endorsed the presence of sleep paralysis. She did not have any restless leg symptoms or insomnia.
Past medical history. Noncontributory.
Medications. Fexofenadine hydrochloride and fluticasone propionate.
Social history. She was a teacher and a part-time bartender. She was single and lived with her boyfriend. She did not smoke or abuse alcohol or drugs. She only used alcohol in social situations.
Family history. This was significant for excessive daytime sleepiness in an aunt whom she thought may have had obstructive sleep apnea.
Review of systems. Negative for any psychiatric problems.
Neurologic examination. Completely normal.
Actigraphy confirmed the patient’s clinical history, showing an average sleep time of 5.5 hours at night during weekdays and 8 to 9 hours during the weekends.
After actigraphy was done, she went on her summer break and increased her daily sleep significantly. Her symptoms resolved over 10 days. No further evaluation was needed.