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Year : 2004  |  Volume : 6  |  Issue : 23  |  Page : 87--91

Effects of low frequency noise on sleep

K Persson Waye 
 Department of Acoustics, Alborg university, Denmark

Correspondence Address:
K Persson Waye
Department of Environmental Medicine, The Sahlgrenska Academy, G�teborg University Box 414, S-40530 G�teborg, Sweden.


Low frequency noise (20-200 Hz) is emitted by numerous sources in the society. As low frequencies propagate with little attenuation through walls and windows, many people may be exposed to low frequency noise in their dwellings. Sleep disturbance, especially with regard to time to fall asleep and tiredness in the morning, are commonly reported in case studies on low frequency noise. However, the number of studies where sleep disturbance is investigated in relation to the low frequencies in the noise is limited. Based on findings from available epidemiological and experimental studies, the review gives indications that sleep disturbance due to low frequency noise warrants further concern.

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Waye K P. Effects of low frequency noise on sleep.Noise Health 2004;6:87-91

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Noises with a dominant content of frequencies in the range of 20 to 200 Hz (low frequency noise) are emitted by a large range of sources in the society. Many of these sources are related to different means of transportation, such as lorries, diesel-driven busses and trains, airplanes and helicopters. Low frequency noise is also emitted by a range of stationary sources related to heating, cooling or ventilation of buildings. Owing to the low velocity speed, low frequencies may propagate for long distances, with little attenuation apart from distance. Low frequencies will also pass with little attenuation through walls and windows. At long distance from the source, or indoors, the noise spectrum will be selectively attenuated, resulting in a spectrum dominated by low frequencies. Airborne noise of a low frequency character may also occur as a result of vibrations in the ground or in constructions. Indoors, room resonances in the low frequency range will increase the sound pressure levels and also lead to variations of sound pressure level inside the room. In order to assess effects occurring indoors, such as sleep disturbance, it is therefore pertinent to carry out measurements indoors.

There are a large number of studies on effects on sleep and well-being due to transportation noises (e.g. Thiessen and Lapointe 1978, Ohrstrom et al 1990, Griefahn 1991, Ohrstrom et al 1998). However, little is known of the content of low frequencies in these intermittent noises as few studies report of no more than the A-weighted sound pressure levels. Regarding effects of steady state low frequency noise from stationary sources some data are available. In the following, a review of available studies on the effects of low frequency noise and sleep disturbance is given. The selection of studies was based on the description of the noise exposure. Information of the C-weighted sound pressure level or preferable, frequency spectra analyses, in addition to the A-weighted level was set as a criterion for inclusion in the review.

 Reports in case studies and epidemiological studies

Several case studies indicate that low frequency noise affects sleep quality, particularly with reference to the time taken to fall asleep and tiredness in the morning (see Berglund et al., 1996, for a review). With the attempt to get more structured information from subjects reported to suffer from infrasound and/or low frequency noise, a questionnaire was distributed to the civic and regional environmental administrations, to the interest group for infrasound and low frequency noise in Denmark and also available on the internet (Moller and Lydolf 2002). In total 198 valid questionnaires were registered during a period of 16 months in 1998-1999. The answers showed that among this selected group the major symptoms were insomnia and concentration problems, reported by 67.5% and 67% of the sample. As no objective information on the sound exposure was available for most of the cases, it is not possible to exclude that other variables other than physical sound exposure were responsible for the symptoms. More information on this matter will be obtained in a currently ongoing study, where a randomly selected sample of these cases is investigated more closely, through e.g. sound measurements in their homes.

A limited number of epidemiological studies have been carried out which give some support to the findings in the case studies. Verzini et al. (1999) found that the energy content of 20 to 160 Hz was significantly related to sleep disturbance, concentration difficulties, irritability, anxiety and tiredness. The study was carried out among 98 subjects living in urban areas with dominant low frequency noise from installations, air condition units, industrial processes and traffic noise from tunnels.

In a cross sectional study comprising a total of 279 persons, no significant differences were detected in reported sleep among people exposed in their homes to flat frequency noise as compared to low frequency noise from ventilation/heat pumps (Persson Waye and Rylander 2001). It was however found that fatigue, difficulty of falling asleep, feeling languid and tensed in the morning were reported to a significantly higher degree among those annoyed by low frequency noise. Furthermore, a significant dose response relationship was found between reported annoyance and disturbed rest and degree of low frequency of the noises. This relationship was still valid after correction for differences in A-weighted sound pressure levels. Third octave band analyses showed that the low frequency exposures were at or above the normal perception threshold (ISO 389-7:1996) in the frequency range of 50 to 200 Hz, while the flat frequency noise was exceeding the normal perception threshold from about 100 Hz and upwards. The sound pressure levels ranged from 26 to 36 dBA and 49 to 60 dBC in dwellings with low frequency noise exposure and from 24 to 33 dBA and 41 to 49 dBC in dwellings with flat frequency noise exposure.

In another investigation, 30 subjects complaining of low frequency noise in their homes were compared to an equal number of subjects of matched age and sex, living in the same block of flats but without the low frequency noise (Mirowska, 1998). A higher occurrence of chronic sleep disturbance and depression was reported among the complainers. The study gives some indications of higher symptoms among complainers, but the results could be confounded by differences between the study populations.

Persson Waye et al (2003,a) investigated annoyance and sleep disturbance in an urban study population (n=41) whose flats on one side (backyard) were exposed to low frequency noise from installations and on the other side (street) were exposed to traffic noise It was found that the proportions of people reporting very or extreme annoyance and disturbed rest due to noise from installation noise among those with bedrooms facing the backyard were 44% and 53% respectively. The corresponding percentages for disturbances to traffic noise among those with bedroom facing the street were 26% and 30%. Average measured indoor levels from installation noise were 31 dBA, 50 dBC with window closed and calculated indoor levels from traffic noise during the night amounted to 21 to 31 dB L Aeq(23-0700) and 50-51 dB LAmax. In both groups a large percentage or 63% reported that sleep was disturbed by some noise, the majority of comments referred to noise from installations and traffic. The reported sleep disturbance was similar among those with bedroom facing the street and among those with bedroom facing the courtyard, except for "feeling tired in the morning" that was reported to a significantly higher degree among those with bedroom facing the street. It should however be acknowledged that the sample in this study was very small and that no correction was done for other factors that could have influenced sleep. Further studies are currently carried out including a larger study population where possible confounders for sleep disturbance can be taken into account.

Of special interest is a cross-sectional study recently carried out by Ising and Ising (2002). It is one of the few studies that have tried to relate the low frequency content in heavy vehicle noise to adverse effects and furthermore looked at a group where data on sleep disturbance due to noise is lacking, namely children. In total 56 children aged 7-10 years living either at a busy road with 24 h lorry traffic or in quiet areas were studied. In the bedrooms, measurements were undertaken of short term maximum sound pressure levels (L Amax , L Cmax ) and equivalent third octave band sound pressure levels from passing lorries. On average every 2 minutes a lorry passed the house. The indoor noise levels of the exposed half of the children were 26-53 dB L Amax , respective 55-78 dB L Cmax, and the frequency spectrum had its maximum below 100 Hz. For the low exposed children the corresponding values were 20-43 dB L Amax and 30-54 dB L Cmax . A significant correlation was found between the maximum levels of low frequencies in the noise, measured as L Cmax , and urine cortisol levels sampled in the first half of the night, while no correlation was found between noise exposure and the excretion of urine cortisol in the second half of the night. The increase of cortisol during the first half of the night was furthermore significantly related to impaired sleep, memory and ability to concentrate. The results indicate that long-term exposure to intermittent low frequency noise at these levels resulted in chronic increases of children's excretion of free cortisol in the first half of the night, and thus disturbance of the circadian rhythm of cortisol.

 Experimental studies

In an early study by Inaba and Okada (1988), six subjects were exposed to sinusoidal tones at 10, 20, 40 and 63 Hz with sound pressure levels ranging from 75 to 105 dB for 10 and 20 Hz and from 50 to 100 dB SPL for 40 and 63 Hz. They found no significant difference between the exposure nights and control nights in sleep efficiency index (sleep time/bedtime), number of changes in sleep stage or changes in the proportion of each sleep stage evaluated by elec�troencephalogram (EEG) recordings. No subjective data on sleep quality, time to fall asleep or tiredness in the morning were recorded.

The effects of night-time exposure to traffic noise and low frequency ventilation noise on the cortisol awakening response and subjective sleep quality were investigated in an explorative study comprising twelve male subjects (Persson Waye et al 2003, b). Subjects slept for five consecutive nights in a sleep laboratory. After one night of acclimatisation and one reference night, subjects were exposed to either traffic noise (35dB L Aeq 22.00- 08.00, 50dB L Amax ) or LFN (40dB L Aeq 22.00�-08.00) on alternating nights (with an additional reference night in between). The frequency spectra of the ventilation noise had its highest sound pressure level of 69 dB at 50 Hz, at which frequency a modulated sinusoidal tone had been added to the original recording in order to give the noise a "rumbling" character (100% amplitude-modulated at 2 Hz). The frequency spectra of the traffic noise had its highest sound pressure levels of 47 and 49 dB at 63 and 80 Hz. Salivary free cortisol concentrations were determined in saliva samples taken immediately at awakening and at three 15-minute intervals after awakening. The awakening cortisol response on the reference nights showed a normal cortisol pattern. The awakening cortisol response following exposure to low frequency ventilation noise was significantly attenuated at 30 minutes after awakening, while the cortisol response after traffic noise was moderately attenuated and not significantly different from quiet reference nights. In comparison to the reference night, subjects took longer time to fall asleep during exposure to low frequency ventilation noise while exposure to traffic noise induced greater irritation in the morning. Interestingly it was also found that lower cortisol levels at 30 minutes after awakening were related to lower mood such as 'activity' and 'pleasantness' in the morning after exposure to low frequency ventilation noise, and poorer sleep quality after exposure to traffic noise. However, in a subsequent study comprising a larger number of subjects and the same low frequency ventilation noise, the effect on cortisol response upon awakening was not reproduced (Persson Waye et al 2003,c). As the exposures to low frequency ventilation noise in the second study were carried out on different weekdays and a significant effect of weekday for the cortisol response was found, it is possible that the conflicting results between the two studies are due to different response pattern over week days.

In agreement with the previous study, subjective sleep was moderately affected after exposure to a low frequency ventilation noise, mainly with regard to tiredness in the morning and mood. The presence of such circaseptan rhythms has been suggested by Maschke et al (2001). There is a need to obtain more precise knowledge of factors affecting the cortisol response in general and the presence of circaseptan rhythms of cortisol in particular before further studies are undertaken.

Recently another study has included low frequency ventilation noise in the experimental design (Ohrstrom and Skanberg, 2003). The effects on sleep after nocturnal exposure to traffic noise, low frequency ventilation noise and a combination of the two exposures were studied in a laboratory study comprising 18 subjects. The equivalent 23-07h A-weighted sound pressure level from traffic was 39 dB, with A-weighted maximum levels of 55�3 dB, while the corresponding levels for the combined exposure was 43dB and 55�3 dB. The ventilation noise was recorded indoors in an office room facing a courtyard with the window 10 cm opened. It had an A-weighted sound pressure level of 40 dB. The frequency spectra of the ventilation sound and combined had its highest sound pressure level of 61dB around 40 Hz, while the traffic noise had its highest sound pressure level of 58 dB around 50 Hz. Effects on sleep were recorded by wrist-actigraph, type mini-motion- logger actigraph from Ambulatory Monitoring Inc. and questionnaires. The results from the wrist�actigraph showed no difference between quiet reference nights and nights with traffic noise or the combined exposure. Fewer number of wake episodes, longer mean sleep episodes and lower number of sleep episodes were found during nights with ventilation noise as compared to the reference night. Contrary to the data obtained from the wrist-actigraphy, subjective evaluations detected a significant decrease of sleep quality for all exposure sounds including the low frequency ventilation noise.

 Concluding comments

The review shows that the numbers of studies where the low frequencies in the sounds can be analysed in relation to effects on sleep are rather limited. This is unfortunate as many of the studies investigating transportation sources could have given more information on this matter had only the noise exposure been more carefully described. The limitations of relevant dose descriptors in many studies are a natural result of the lack of an international agreement both with regard to definition of a low frequency noise and with regard to description of the exposure. Furthermore, in order to get a satisfactory comprehension between sounds and effects, future studies should not only describe the equivalent sound pressure levels in the frequency range, but also evaluate the influence of temporal structures, such as level fluctuations and degree of intermittency.

As the research area is rather new there is a need to investigate mechanisms and models for sleep disturbance due to low frequency noise in experimental studies. Present studies are not conclusive with regard to objectively measured effects. Subjective data do however support the observations in field studies that low frequency noise, at comparatively low sound pressure levels, disturbs sleep. It is however important to continue the search for methods that are reliable, valid and that cannot only be used for acute exposure, but also have some bearing for chronic exposures. In order to overcome some of the disadvantages of experimental exposures, with regard to the novel environment etc there is a movement towards exposing subjects to recorded noise in their home settings. For noise in general and low frequency noise in particular, it is essential to have control of the sound field as the noise exposures otherwise will show large variation between rooms and hence subjects.

Revised epidemiological studies are all except one, based on measurements carried out indoors, which is necessary in order to get a satisfactory assessment of the exposure. These types of studies are therefore time- and resource consuming which may be one reason for the rather small study populations included. However the small sample sizes limit the possibilities to find effects on sleep and health and there is a need for larger studies or new approaches in this field of research. Larger studies are also a prerequisite for the possibility to control for variables that could covary with sleep disturbance. The reported sleep disturbance and findings of dose response relationships between the presence of low frequencies in a noise and annoyance and disturbed rest motivate however further research into this area. There is also some support that the low frequencies in transportation noise may be of relevance for chronic effects related to disturbed sleep[17].


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