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|Year : 2010 | Volume
| Issue : 47 | Page : 64--69
Sleep, noise and health: Review
Mia Zaharna, Christian Guilleminault
Stanford Medicine Outpatient Center, Sleep Medicine Division MC5704, Redwood City, CA 94063, USA
Stanford Sleep Medicine Center
Sleep is a physiologic recuperative state that may be negatively affected by factors such as psychosocial and work stress as well as external stimuli like noise. Chronic sleep loss is a common problem in today's society, and it may have significant health repercussions such as cognitive impairment, and depressed mood, and negative effects on cardiovascular, endocrine, and immune function. This article reviews the definition of disturbed sleep versus sleep deprivation as well as the effects of noise on sleep. We review the various health effects of chronic partial sleep loss with a focus on the neuroendocrine/hormonal, cardiovascular, and mental health repercussions.
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Zaharna M, Guilleminault C. Sleep, noise and health: Review.Noise Health 2010;12:64-69
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Zaharna M, Guilleminault C. Sleep, noise and health: Review. Noise Health [serial online] 2010 [cited 2020 Aug 14 ];12:64-69
Available from: http://www.noiseandhealth.org/text.asp?2010/12/47/64/63205
Chronic sleep loss is a widespread problem. In today's society, our around-the-clock lifestyle, increasing work pressure, and psychosocial stressors are major contributors for chronic sleep loss. Similarly, external stimuli often disturb or reduce sleep length, for instance, due to noise, one of the most frequent ambient factors.  As these less than ideal conditions become more pronounced, it is important that we understand the effects of chronic sleep loss. It is well established that after an acute period of sleep loss, the body responds by attempting to catch up by making us sleep more and more deeply the following night. This is the body's method of trying to maintain a homeostatic balance between sleep - our main physiological recuperative state - and wakefulness. Less is known, however, about the health consequences of chronic partial sleep loss, that is, gradually losing small amounts of sleep over a period of days, months or even years.
Chronic partial sleep loss may have many repercussions on health; however, many of these effects are still unknown. Most individuals have, at one time or another, experienced the effects of acute sleep deprivation. Controlled studies most commonly report negative effects of sleep deprivation on our cognitive functions and moods. ,, Recent studies demonstrated that successive nights of restricted sleep resulted in gradually accumulating decline in cognitive function. ,, While subjects may recover from these effects after a few nights of sleeping,  chronic sleep loss may contribute to physiologic changes that accumulate over time and may result in serious health consequences.  Recent studies report, for instance, that chronic partial sleep loss of even 2-3 h per night has detrimental effects on the body even in cases where individuals did not experience any subjective sense of sleepiness. , Detrimental effects from sleep loss include impairments in cognitive performance, as well as cardiovascular, immune and endocrine functions. , Sleep disturbance from prolonged exposure to noise has been associated with similar negative effects on mood and performance as well as cardiovascular and endocrine function. ,, Many factors can be considered when looking at the effects of noise on health such as the nature of disturbed sleep, the relationship between noise and sleep disturbance, as well as the adverse health consequences that result.
There is an important distinction between sleep deprivation and sleep disturbance. Both sleep deprivation and sleep disturbances are commonly found in normal individuals as well as individuals diagnosed with a sleep disorder. Sleep deprivation is an acute or chronic lack of sufficient sleep, whereas sleep disturbance encompasses multiple disorders including insomnia, circadian rhythm disorders, and sleep-related breathing disorders, to name a few. The International Classification of Sleep Disorders (ICSD-2) includes over 70 specific diagnoses within the eight major categories, as well as two appendices for classification of sleep disorders associated with medical or psychiatric disorders.  Sleep deprivation creates problems that are often thought to be related to insufficient quantities of sleep, whereas sleep disturbances include disorders relating to sleep fragmentation, affecting the quality of sleep. Primary sleep disturbances include difficulty falling asleep, frequent awakenings, waking too early, and alterations in sleep stages and depth, especially a reduction in rapid eye movement (REM) sleep. Factors associated with sleep disturbance primarily involve individual environmental conditions. This includes parameters in the immediate environment such as ambient temperature, humidity and light, as well as other environmental parameters like noise and vibration, for example. A combination of these factors as well as reactivity of the individual determines the degree of sleep disturbance experienced. 
The 2002 National Sleep Foundation Sleep in America poll  suggests that as many as 47 million American adults suffer from a sleep disorder. Insomnia, defined as difficulty falling asleep, waking often during the night, waking up too early and not being able to get back to sleep, and waking up feeling unrefreshed, is the most common sleep disorder. More than one-half of the respondents of the poll (58%) reported having experienced at least one of the four symptoms of insomnia at least a few nights a week, and 35% have experienced at least one of these four symptoms of insomnia every night or almost every night in the past year. Although chronic partial sleep loss is a common complaint among many individuals in today's society, the exact prevalence remains unknown. Epidemiological studies suggest that mean sleep duration has decreased substantially as proportionally more people are awake for longer periods of time.  The 2002 Sleep in America poll shows that, on average, individuals sleep 6.9 h a night on weekdays and 7.5 h on weekends. Over a quarter of people rate their sleep quality as fair or poor. 
Noise and Sleep
By disrupting the known restorative function of sleep, noise is a prevalent and harmful cause of sleep disturbance.
Sleep patterns are particularly susceptible to noise for a number of reasons. First, our brains are able to process incoming acoustic stimuli even while asleep. Second, the noise levels that effect sleep are much lower than those required to impair hearing. The World Health Organization guidelines say that for a good sleep, sound level should not exceed 30 dB(A) for continuous background noise, and 45 dB(A) for individual noise events.  During sleep the levels that cause noise-induced stress reactions are much lower than in the active phase. Furthermore, a subject may sleep during relatively high noise levels but still show autonomic responses, such as increased heart rate.
The effect of noise on sleep, however, not only depends on the acoustical parameters of noise but also on the individual as there is large variance in the experience of a person with a particular noise. Personal characteristics such as personality traits, diurnal type, age and self-estimated sensitivity to noise are important individual factors. ,, Noise-induced sleep disturbance is proportional to the amount of noise experienced in terms of increased rate of changes in sleep stages and in number of awakenings. 
Acute primary effects of noise on sleep disturbance involve changes on the polysomnogram starting with a K-complex followed by increased brain activity with body movements and autonomous responses. Total time awake and/or total shallow sleep (stages 1 and 2) increases at the expense of slow wave sleep and REM sleep. Reducing indoor noise levels can increase the amount of slow wave sleep and REM sleep.  Secondary subjective effects of environmental noise causing disturbed sleep include impaired self-estimated sleep quality, mood and performance. 
Chronic exposure to an environmental noise (EN) induces sleep disturbances although it is not fully known what impact these disturbances have on humans. In one study, rats were exposed to environmental noise for 9 days. Results showed that this chronic exposure continually restricted the amount of slow wave sleep (SWS) and paradoxical sleep (PS) and fragmented these two sleep stages with no habituation effect.  As previously mentioned, autonomic responses to noise during sleep can be obtained for much lower peak noise intensities as during wake states. These effects, mainly involving increased heart rate and vasoconstriction, have been found to habituate over successive noise-exposed nights as opposed to long exposure times. This could indicate an effect on cardiovascular response over the long term. 
Similarly, several studies demonstrate next day effects in humans after sleep disturbance. Noise exposure during sleep may increase blood pressure, heart rate and finger pulse amplitude as well as body movements.  During the day following disturbed sleep by road traffic noise, after effects such as decreased perceived sleep quality, mood and performance in terms of reaction time were found. 
Epidemiological studies have focused on the impact of noise on individuals such as patients in hospitals and the impact of particular sources of noise (e.g., aircraft) on sleep. The Health Council of the Netherlands considers the evidence to be sufficient to establish a causal relationship between the long-term effects of noise-related sleep disturbances, and changes in sleep patterns, awakening, sleep stages and subjective sleep quality.  Some individuals may be more susceptible to noise occurring during sleep, as well as in the waking state, with day and night noise being a significant problem for night workers, mothers with babies, elderly persons, persons who are especially vulnerable to physical or mental disorders, and other individuals who experience sleeping difficulty.
It still remains questionable whether environmental noise has any long-term detrimental effects on health. Most studies are of relatively short duration (between 3-16 nights) due to the expense and effort involved with exposing participants in studies to long-term noise exposure and sleep monitoring. One study did follow subjects for 40 days.  Thirty subjects were monitored on a 24-h tone pulse for a 30-day exposure period and a 10-day post-exposure period. No significant change was found in mean heart rates at night, total body movements during the night, objective sleep latency, total hours of sleep, number of awakenings and percent time for sleep stages.
To summarize, the causal relationships between noise exposure, effects on sleep, and contribution to chronic disease, behavioral changes, and changes in physical, mental and social well-being are not yet firmly established. Therefore, the significance of the various primary and secondary effects of noise on sleep disturbance cannot be adequately assessed without further long-term research.
Health Effects of Disturbed Sleep
It is difficult to identify the cumulative effects of chronic partial sleep loss prior to their emergence as a major pathology. Historically, sleep has been viewed as a means to prevent fatigue and exhaustion.  Current understanding, however, indicates that sleep has important physiologic restorative functions. An improved understanding of physiologic activities during normal sleep has shed light on the important cardiovascular, neuroendocrine, immunologic and behavioral/cognitive changes associated with disturbed sleep. Over the last decade, experimentally based data were collected on chronic restriction of sleep (by 1-4 h at night), accumulating daytime sleepiness and cognitive impairment.  Most individuals develop cognitive deficits from chronic sleep debt after only a few nights of reduced sleep quality or quantity; new evidence suggests additional important health-related consequences of sleep debt related to common viral illnesses, diabetes, obesity, heart disease, depression and other age-related chronic disorders.  Next, we review current knowledge on chronic sleep disturbance and effects on health.
Neuroendocrine and hormonal effects
The main neuroendocrine systems involved in the human body's response to stress are the autonomic sympatho-adrenal system and the hypothalamic-pituitary-adrenal (HPA) axis. , Stress is defined as a nonspecific physiologic response to any kind of demand that an organism faces.  Sleep disruption acts as a stressor and results in activation of these classical stress systems. The sleep state has a suppressive effect on the stress system and results in lower plasma levels of stress hormones such as cortisol and adrenaline.
Sleep deprivation has been shown to create a higher activity level of these stress systems resembling that seen in the wakeful state. However, it is not certain whether sleep deprivation increases the stress system activity to a point beyond what is seen in relaxed wakefulness.  One study showed that partial sleep deprivation, where sleep was restricted to 4 h a night for six nights, resulted in increases of cortisol only in the afternoon after the partial sleep loss. The study, however, also noted that, in these healthy young men, glucose tolerance and glucose effectiveness after partial sleep loss were similar to that seen in aging or in gestational diabetes. Paying off the sleep debt by extending subjects' sleep for 1 h for one week completely normalized the impaired glucose tolerance. 
Sleep deprivation and sleep disruption significantly affect cortisol and adrenocorticotropic hormone (ACTH) secretion. Several studies have shown that stage one sleep and awakenings during sleep are associated with increased cortisol concentrations. , In contrast, one study showed that sleep fragmentation and sleep deprivation substantially altered the patterns of cortisol secretion although average cortisol concentration was not significantly changed. This study compared the influence of temporary sleep deprivation to arousals continuously induced during sleep on pituitary-adrenocortical activity in 10 healthy subjects. Sleep disruption introduced during the second REM epoch did not alter the average release of ACTH and cortisol during the night.  However, there was an initial cortisol peak following the initial introduction of sleep disruption. This study suggested that sleep attenuates negative feedback inhibition within the HPA system, whereas wakefulness (or stage 1 sleep) reflects increased feedback sensitivity of this system.
Patients with sleep apnea have been shown to display decreased growth hormone and prolactin secretion at night. , This decrease was observed to reverse after sleep was normalized, suggesting that the cause was sleep fragmentation. Still, such changes in hormone levels have not been studied separately in sleep fragmentation (i.e., not resulting from sleep related breathing disorder or to sleep deprivation).
The majority of sleep literature has focused on hormonal effects of total sleep deprivation. Thyroid activity, including TSH, T3, and T4 levels, is increased by sleep deprivation.  Minimal changes in adrenal and sex hormones have been found. Insignificant changes in cortisol, adrenaline, catecholamine output, hematocrit, plasma glucose, creatinine and magnesium are seen in total sleep deprivation.  However, patterns of secretion may change even if the total amount of hormone secretion remains relatively unaltered. Moreover, prolactin, noradrenaline and growth hormones seem to lose their periodic pattern of excretion during times of sleep deprivation. ,
In summary, chronic sleep loss, including those related to chronic noise exposure, could lead to development of various problems, both centrally and peripherally, associated with glucocorticoid excess including memory deficits and insulin resistance.
Cardiovascular effects/autonomic nervous system
During sleep, heart rate is related to changes in the parasympathetic-sympathetic balance with an increase in sympathetic tone associated with activation and with electroencephalogram(EEG) arousal. Catecholamine levels and sympathetic activity decrease during sleep. So, as one might assume that decreased sleep is associated with increased sympathetic activity and as a result increased blood pressure and heart rate. This association has been observed not only with sleep deprivation but also with regard to sleep disruption. Brief awakenings from sleep for only a few seconds are associated with temporary elevation in blood pressure and heart rate that results from an autonomic reflex.  One study reports heart rate acceleration with auditory stimulation during sleep even when no EEG arousal was observed. These findings thus question whether activation of the autonomic nervous system night after night without visual EEG arousal or alpha-alpha-beta EEG changes of shorter duration could have long-term detrimental effects on the cardiovascular system. By contrast, the results suggest that brain stem activation can lead to autonomic nervous system response without creating objective consequences on specific tests of psychomotor vigilance during the following day. 
Behavioral/cognitive/mental health effects
There is sufficient literature that documents the detrimental effects of chronic partial sleep loss on behavior, cognition and mental health conditions. The fact that many individuals live in a state of chronic partial sleep loss highlights the importance of understanding and quantifying the effects of sleep loss on daily functions.
Studies report that total and partial sleep deprivation cause changes in mood and cognition such as increased sleepiness, fatigue, irritability and an overall decrease in concentration. , Other effects of sleep deprivation include longer reaction times, poor short-term memory, reduced motivation, distractibility and poor performance.  Effects of sleep fragmentation are similar. On days following disturbed sleep, psychomotor performance is impaired and subjective sleepiness is higher. Changes in multiple sleep latency test (MSLT) with sleep fragmentation suggest that sleepiness increases as the rate of fragmentation increases.  Several studies have examined whether these effects are due to changes in the amount of sleep stages (for example, increases in stage 1 sleep) or losses of slow wave sleep. ,,, These studies indicate that the effects of sleep fragmentation on sleepiness, as measured by MSLT and maintenance of wakefulness test (MWT), are caused primarily by sleep continuity disturbances rather than changes in sleep stages.
Sleep fragmentation has also been shown to impair functioning even when the total amount of sleep time remains relatively unchanged. In a recent study the sleep of 11 subjects was disrupted by an audiometer on two consecutive nights. The results suggest that periodic disruption of sleep quickly results in impaired functions comparable to that of 40-64 h of total sleep loss. The disruption procedure resulted in severely fragmented sleep with only a small amount of slow wave and REM sleep, even though the total amount of sleep time was reduced by only 1 h per night.  A different study showed that MSLT was reduced after both total sleep deprivation and 1-min sleep fragmentation. There was, however, no statistical difference in sleep latencies between the two groups (sleep latency of 2.2 min in the total sleep deprived group and 4.1 min in the sleep fragmented group).  Finally, one study showed similar deficits in vigilance hit rate and nap latency but greater deficits in performance following total sleep deprivation as compared to 1-min sleep fragmentation. 
Sleep disordered breathing has been associated with impaired cognitive function as a result of various factors including chronic partial sleep loss from insufficient nocturnal sleep with sleep architecture changes. , Reported effects include deterioration in memory, intellectual capacity and motor coordination as well as decline in ability to perform psychomotor vigilance tasks including visual reaction and auditory learning. , Personality changes, irritability, depressive symptoms and an increased proneness to accidents have been observed as well. ,
Environmental factors, such as work pressure, lifestyle choices and noise are major causes of sleep disturbance. Because sleep is a crucial physiological recuperative state, sleep disorders are a cause of many negative health effects. Such effects include, but are not limited to, cardiovascular problems, neuroendocrine abnormalities and changes in cognition, mood and memory. The causal relationships between noise exposure, effects on sleep, and contribution to health disturbances, both behavioral and physical, are not yet firmly established. Many of the health effects noted have been shown in studies looking at conditions leading to sleep fragmentation and secondary sleep restriction. Even if noise has been used experimentally to induce these fragmentations, our understanding of the effects of chronic noise and the role of intermittent versus continuous noises on health as example is still limited and justifies further investigations.
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