|Document "The Influence of Night-time Noise on Sleep and Health": English Abstract|
Why this report?
Sleep is very important. It is therefore understandable that unintentional noise-related disturbance of sleep is a serious problem. Like other countries, the Netherlands has regulations designed to limit public exposure to environmental noise, primarily with a view to managing the associated nuisance.
Most of the limits relate to exposure over a complete twenty-four-hour period and do not therefore focus specifically on the period during which most people sleep. However, regulations are presently being prepared at EU level that do concentrate on night-time noise exposure. In due course, Dutch law will be brought into line with the new EU legislation.
Against this background, the State Secretary for Housing, Spatial Planning and the Environment wrote to the Health Council on 3 February 2003, asking for its advice regarding the influence of night-time noise on sleep, health and well-being. This report has been compiled by the Council’s Noise, Sleep and Health Committee and addresses the questions posed by the State Secretary.
Exposure to night-time noise when sleeping
Environmental noise may originate from a wide variety of sources: air, road or rail traffic; industry and other localised activities; neighbours or one’s general neighbourhood.
The consequences of exposure to night-time noise when sleeping have mainly been studied in relation to traffic noise. Little research has been conducted into sleep disturbance from localised noise sources such as factories, firing ranges, shunting yards, wind turbines, climate control systems, building or demolition work. However, the Committee believes that the effects of noise from such sources are unlikely to differ essentially from the effects of traffic noise.
Published research findings indicate that a variety of non-acoustical factors determine whether people are disturbed in their sleep by noises from neighbouring homes (voices, toilet flushing, footsteps, radio, television). The existence and complexity of these factors imply that it is not possible to establish meaningful relationships between night-time noise from neighbouring dwellings and the degree of sleep disturbance one suffers.
Effects of night-time noise during sleep
Biological responses to environmental noise occur because, even when asleep, an organism has to appraise and process stimuli from its environment. Such responses include waking up, having difficulty falling asleep again and increased motility.
It is plausible that, in the event of repeated exposure to night-time noise and under certain circumstances, some biological responses will have long-term implications for health and well-being. The Committee distinguishes five categories of effects: • reduced sleep quality • reduced general well-being • impaired social interaction and reduced concentration during day-time • specific disease symptoms • loss of years of life (premature mortality).
There is sufficient evidence that night-time noise events cause direct biological responses, such as increased heart rate, reduced depth of sleep, increased motility and awakening.
Most biological responses begin to manifest themselves at an SEL in the bedroom of approximately 40 dB(A) (LAmax in the bedroom of at least 32 dB(A)). Behavioural awakening (established by pressing a button) occurs when the bedroom SEL exceeds 55 dB(A).
The Committee also concludes that there is sufficient evidence of a relationship between exposure to night-time noise and a variety of biological responses exhibited before, during and after sleeping. Some of these are consequences of the direct responses already referred to: increased average heart rate, increased average level of motility, more frequent behavioural awakenings, and longer intervals of wakefulness. It additionally appears that average motility in people exposed to night-time traffic noise is greater at higher noise levels than might be expected on the basis of the direct responses.
Higher levels of average motility are closely related to more frequent awakening, lower perceived sleep quality and increased daytime drowsiness.
Furthermore, there is sufficient evidence that people who, while attempting to sleep, are exposed to environmental noise or are concerned about being disturbed by noise in the night, have more difficulty falling asleep. After the sleep period, those who were exposed to night-time noise perceive the quality of their sleep to be impaired, find that their daytime mood is adversely affected and experience greater drowsiness, fatigue and irritability, especially in the morning.
There is limited evidence that under certain circumstances night-time noise can influence stress hormone levels. This effect was observed in women who were annoyed by noise at night and unable to protect themselves adequately to prevent the annoyance.
Implications for health and well-being
The Committee believes there is sufficient evidence that night-time noise has an adverse effect on quality of sleep and general well-being. Limited evidence exists that exposure to night-time noise has a negative impact on social interaction, on the performance of concentration-sensitive tasks during the day, on specific complaints or disease symptoms and on loss of life years due to fatal accidents at work.
Reduced sleep quality is evident from studies on reduced self-reported sleep quality, difficulty falling asleep and remaining asleep, more frequent awakening during the night, shorter sleep periods and increased motility during sleep. A reduction in general well-being due to night-time noise is evident from self-reported sleep disturbance, selfreported health problems, use of sleeping pills and sedatives, and adversely affected daytime mood. Among older people in particular, the use of sleeping pills and sedatives is increased by night-time noise.
The medical conditions that may be linked to exposure to night-time noise are insomnia, high blood pressure and cardiac disease, as well as depression in females.
Where insomnia is concerned, the Committee considers the evidence of a causal relationship as sufficient, while there is limited indirect evidence for the three latter conditions.
There is also limited indirect evidence of an increased risk of involvement in a fatal accident at work as a result of sleeping problems and insomnia associated with exposure to night-time noise.
A special metric for night-time noise
In 1997, the Health Council recommended a system with two noise indicators to protect the public from traffic and industrial noise in the living environment. The Committee has taken up this proposal. According to the system put forward in 1997 the metric of exposure to noise over a twenty-four-hour period should be representative of general annoyance, while the night-time noise metric should be related to sleep disturbance. Such an approach is rational since there is only a limited degree of comparison between the working mechanisms and effects of night-time noise on the one hand and general annoyance on the other hand.
In addition to Lden, the indicator of noise over a twenty-four-hour period, the European Union has adopted Lnight, an indicator to be used in the regulation of night-time noise. Lnight represents the noise exposure at the most exposed façade, calculated for an eight-hour night-time period (11pm to 7am), and averaged over a full year. In the calculations, more weight is given to the louder noise events than to the quieter ones. Since Lnight relates to the outdoor situation, the noise exposure in a person’s bedroom may in practice be considerably higher than Lnight minus the average noise attenuation of a Dutch home. This is partly because homes differ considerably in the attenuation they provide (in the Netherlands, only newly built homes have to meet noise attenuation standards), and partly because most Dutch people choose to sleep with their bedroom windows at least slightly open. Furthermore, requirements on the basis of Lnight can never provide complete protection against sleep disturbance, since many Dutch people go to bed before 11pm and still more (roughly half of all adults) sleep beyond 7am.
Nevertheless, the Committee sees no benefit in adopting an alternative to Lnight, since it realises that it is impossible to address every conceivable factor by means of a regulatory noise metric. Furthermore, the Committee is of the opinion that regulations based on the use of Lnight (as well as Lden) could provide a considerable degree of protection against noise during sleep.
Recommendations for future research
The Committee recommends that studies be carried out into various topics, in order to fill what it considers to be the most important gaps in our knowledge regarding exposure to night-time noise. These topics are the long-term effects of night-time noise on health and well-being, the effects of night-time noise on children, the effectiveness and efficiency of noise attenuation measures for façades and between dwellings, and the effects of noise produced by neighbours or by one’s general neighbourhood. The Committee advocates that such studies be linked to international programmes, as the Health Council has indeed already proposed in its advisory report entitled Gezondheid en milieu: Kennis voor beleid (Environmental Health: Research for Policy).
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