PROCEEDINGS of the
23rd International Congress on Acoustics
9 to 13 September 2019 in Aachen, Germany

Epidemiological study on long-term health effects of low-frequency
noise produced by wind power stations in Japan
Tatsuya ISHITAKE1; Yoshitaka MORIMATSU1; Kunio HARA2
1
2

Kurume University, School of Medicine, Japan

University of Occupational and Environmental Health, School of Health Science, Japan

ABSTRACT
We investigated whether long-term exposure to wind turbine noise (WTN) including low-frequency noise
generated by wind power facilities is a risk factor of sleep disorders. We performed an epidemiological studyof living environment and health effects, surveying 9,000 residents (≥20 years) living in areas with
operational wind power facilities. Sleep disorders were assessed using the Athens Insomnia Scale. To assess
environmental noise in residential areas near the wind turbines, low-frequency sound exposure levels were
measured at 50 community centers of the town. Multiple logistic regression analysis was used for evaluationof a risk factor for several noise exposure indices. Significant relationships between the distance from thenearest WT to dwellings and hearing, annoyance, sleep disorders were observed. By multiple logistic
analysis the prevalence rate of sleep disorders was significantly higher for residents who reported
subjectively hearing noise being than for those who did not. Moreover, the reported prevalence rate of sleep
disorders was significantly higher in residents living at a distance of ≤1,500 m from the nearest wind turbine
compared to that for residents living at a distance ≥2,000 m. The attitudes of residents towards wind power
facilities and sensitivity to noise strongly affected their responses regarding sleep disorder prevalence.
Keywords: audible noise, epidemiology, infrasound, low-frequency noise, sleep disorder, wind turbine noise

1. INTRODUCTION
The effect of the noise of wind power generation facilities on health is a growing concern. This isespecially true regarding infrasound, defined as sound lower in frequency than 20 Hz. Plans for new
wind power generation facilities have had to be changed in some cases in Japan due to the healthconcerns of local residents.
Multiple cross-sectional epidemiological studies have shown a strong relationship between
annoyance and living in close proximity to wind turbines. It has been reported that individual factors
such as the visual impact of wind turbines, attitudes towards wind turbine installation, and economic
benefits are more strongly related to the presence or absence of annoyance than the actual noise ofwind turbines (1).
Other studies have reported that rather than focusing on the noise of wind turbines, more attention
should be paid to cofounding factors such as attitudes toward wind power generation, impact on
scenic views, economic benefits, visibility of wind turbines, sensitivity to sound, and concerns about
health (2).
Previous epidemiological studies have frequently reported that audible noise generated by windturbines is significantly associated with annoyance and sleep disorder (3, 4). On the other hand, noclear relationship has been reported thus far between infrasound and effects on health (5).
Furthermore, most epidemiological studies have used a cross-sectional design, and therefore cannot
confirm a causal relationship between wind turbine noise and health effects.
The present cross-sectional epidemiological study targeted local residents in Japan where wind
power generation facilities were already active, and sought to determine how exposure to infrasoundand noise from these facilities in Japan affects health, specifically the presence of a sleep disorder.

1

tishitak@med.kurume-u.ac.jp1455

2. METHODSThe target area is Nagashima-cho, Izumi-gun on Nagashima Island, located in the northern part ofKagoshima prefecture. Its population is 10,400. The island is longer in the north-south direction,with an area of approximately 110 km 2. The middle of the island is mountainous, and ports arelocated around the island perimeter. Wind power generation facilities (output 2.4 MW x 21 stations,wind speed rate 12.5 m/s) were introduced in August 2008, in the middle of the island. Most
residences are located at least 1 km from the closest wind turbine, and there are no r esidences within
500 m of a wind turbine.
We conducted this survey by distributing a questionnaire to residents of Nagashima -cho aged 20
years and older (approximately 9,000 people) in December 2014. The survey was distributed to eachhousehold via a circulation board, a traditional method of disseminating information in Japaneseneighborhoods, in cooperation with 57 directors of public city halls (local cultural centers, one ineach school district, providing recreation and learning for local residents). Participants returned thequestionnaire using a prepaid return envelope.
The questionnaire contained items addressing family structure, family residence, living
arrangement, lifestyle, social and economic factors, health conditions, level of annoyance wit h windturbine noise, attitude towards installation of wind power generation facilities and reaction to theirvisual impact, as well as basic personal attributes (gender, age, height and weight). The presence of asleep disorder was evaluated using the Athens Insomnia Scale (AIS) (Japanese version). The AIS
was developed in 2000 by the World Health organization (WHO) based on the 10 th version of theInternational Statistical Classification of Diseases and Related Health Problems (ICD -10), and its
Japanese version was created in 2013. The first five items of the questionnaire pertain to difficulty insleep induction, awaking during the night, early morning awakening, sleep duration and quality ofsleep. The remaining three items consist of questions related to sleepiness, sense of well-being andthe level of active functioning during the day. Each response uses a 4 -point Likert-type scale (0 = noproblem, 1 = minor problem, 3 = considerable problem, 4 = serious problem), and the total iscalculated (range 0–32). A score of more than 6 points indicates the presence of a sleep disorder.
The distance from each household residence to the nearest wind turbine was defined using a
proxy, namely the distance from the wind turbine to the public city hall of the school district inwhich the residence was located. The relationship between sleep disorders and noise was reviewed
using the following four noise-related indicators: 1) whether or not the noise was consciously
audible, 2) horizontal distance from the wind turbine to the district public city hall, 3) wind turbine
noise at night (the A-weighted equivalent sound level (L Aeq )) and 4) difference between wind turbine
noise and background noise.
A summary of the measurement method is as follows. Research was conducted to determine theinfrasound/noise attenuation curve over distance from the wind power generation facility. A
broadband sound pressure level meter was used to measure the level of infrasound and noise at the
public city hall of each school district. Since the measurement of infrasound is easily affected bywind, we covered a microphone with a two-layer wind-proof screen. Assessment of infrasound/noise
exposure levels at the public city halls was conducted for 24 consecutive hours once per season in2014, at 72 locations; these locations were inside 47 public city hal ls among 57 public city
halls/meeting facilities in Nagashima-cho, mainly located in the center of the island. The A-weighted
equivalent continuous sound level L Aeq,10min was calculated based on each hour of infrasound/noise
was detected from the wind power generation facilities, then the mean energy was derived from theentire time range and the wind turbine A-weighted equivalent continuous sound level L Aeq,WTN was
calculated at each measurement point. Regarding the total noise, the A -weighted equivalentcontinuous sound level for every hour and the sound pressure level of noise changes over time were
calculated, then the sound pressure levels during daytime (6:00 to 22:00) and nighttime (22:00 to6:00) were derived using the arithmetic mean for the percentile sound pressure levels and the meanenergy for the A-weighted equivalent continuous sound levels.
Statistical analysis used the chi-squared test and multiple logistic regression analysis. Threemodels were evaluated using multiple logistic regression analysis: model 1, adjusted by gender andage; model 2, adjusted by the variables in model 1 as well as by three social factors, namely shift
work, income and marital status; and model 3, adjusted by the variables in model 2 as well as by theattitude towards the visual impact of the wind turbines and the current attitude toward the original
wind turbine installation. The distance from the residence to the wind turbine was divided into fivecategories: less than 1,000 m; between 1,000 and 1,500 m; between 1,500 and 2,000 m; between

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2,000 and 5,000 m; and 5,000 m and above. There were 2,593 responses to the survey (collection
rate 28.3%). Of these, 401 were disqualified due to missing gender or age (75 responses), missing
city hall district (29 responses), and age 80 years old or older (287 responses). The final number ofqualified survey responses was 2,192.

3. RESULTS
3.1 Participants characteristics and living arrangements
Table 1 shows the participants characteristics and living arrangements. The mean age was 58.1
years, and the gender ratio of males to females was 1.06. Regarding the most common living
arrangements, 90.2% of participants lived with family and 82.3% had lived in the same residence for10 years or more. The rates of smoking and drinking on an almost daily basis were 17.8% and 33.5%,
respectively, with a significant difference between males and females. Approximately 40% agreed
that “the wind turbine is visible from home,” and approximately 15% agreed that “the sound of thewind turbine is audible from home.” The mean distance from the closest wind turbine to each public
city hall was approximately 3,000 m, and the minimum distance was 730 m. The mode of the
distance category was 2,000 to 5,000 m, accounting for 56% of responses. The mode of the nighttime
wind turbine noise level category was 20-50 dB.

3.2

Relationship between audible noise and distance to wind turbine and prevalence ofsleep disorders

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Figure 1 shows the proportion of participants who reported hearing the sound of wind power
generation facilities at home, categorized by distance from their public city hall to the nearest windturbine. For distances less than 1,000 m, 63% reported that the noise was audible, and thispercentage decreased significantly with increasing distance. Even at distances of 5,000 m and over,
2% of respondents stated that the turbines were audible. Sleep disorder (AIS ≥ 6 points) was present
in 26% (528 people) of participants, but this percentage was approximately 40% in those whose
homes were less than 1,000 m from a wind turbine (Fig. 2). The frequency of sleep disorderdecreased to 22% at a distance of 2000 m to 5000 m, but then increased to 30% at a distance of 5,000
and over. There was a statistically significant relationship between distance and sleep disorderfrequency (p < .001).

3.3

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Multiple logistic regression analysis

Multiple logistic regression analyses were performed with the presence of a sleep disorder as anindependent variable, and the wind turbine noise indicator was modeled considering the following
dependent variables: 1) whether or not wind turbine noise was consciously audible, 2) distance fromthe resident’s public city hall to the wind turbine, 3) nighttime wind turbine noise (L Aeq ) and 4)
difference between wind turbine noise and background noise. The results of this analysis are shownin Tables 2 to 5. In every model, participants who agreed that “wind turbine noise is consciously
audible” had approximately twice the odds of having a sleep disorder as those who responded
negatively, and this difference was statistically significant (Table 2). As for the impact of distance tothe wind turbine, residents who lived within 1,500 m were approximately twice as likely to have asleep disorder as those who lived at least 2,000 m away, indicating a statistically significant
difference (Table 3). In terms of exposure to nighttime wind turbine noise ( L Aeq ), those exposed to 35
dB or more had a 1.5-fold higher likelihood of having a sleep disorder than those exposed to thetypical level of 20–25 dB, again a statistically significant difference (Table 4). Finally, regarding thedifference between wind turbine noise and background noise, participants exposed to a difference of
5 dB or more had an approximately 1.6-fold higher likelihood of having a sleep disorder than those
exposed to a difference of less than 5 dB, indicating a statistically significant impact (Table 5).

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4. DISCUSSION
This epidemiologic study suggested that audible noise (frequency of 20 Hz or over) that is
produced by wind power generation facilities can be a risk factor for sleep disorder when theresidential environment is characterized by any of the following: 1) wind turbine sound isconsciously audible, 2) residence is close to a wind turbine (within 1,500 m), 3) nighttime windturbine noise (L Aeq ) is 35 dB or higher and 4) difference between nighttime wind turbine noise andbackground noise is 5 dB or more. The results of multiple logistic regression analysis showed thatthe odds ratio of sleep disorder were significantly increased in these cases. This study used anighttime wind turbine noise (L Aeq ) level of 35 dB and over since this level matched the cut-off value
for annoyance and sleep disorder reported by Schmidt et al (6). This same value is used in windturbine noise standard guidelines worldwide, including in Sweden and New Zealand (7). Japanpreviously had no standards regarding wind turbine noise, but recently the Ministry of theEnvironment released an administrative notice indicating that the noise limit is 5 dB above the1460

background noise, but this standard is not used consistently across the country. The standard
regarding the upper limit for nighttime wind turbine noise takes into consideration the characteristics
of each area to make sure that no troubles arise in the living environment. The upper limit is set to 35
dB in some areas (especially those requiring greater degrees of silence) while other areas have 40 dB
as the limit (8).
As for sleep disorder caused by infrasound, all wind turbine noise of 20 Hz or under that wasmeasured in this study was below the human sensory threshold. The results are not shown, but in a
sub analysis of participants who stated that wind turbine sound was inaudible (n = 1,813), thesignificant relationship between distance and sleep disorder disappeared, and thus the likelihood of a
relationship between the two is low. Noise measurement results near wind power generation
facilities across Japan showed that infrasound was not louder than other environmental noise.
However, the amplitude modulation of sound and tonal components of noise generated from wind
power generation facilities have a tendency to increase annoyance, and therefore further studies
should evaluate their health effects. Jeffery et al.(3) also reported that even if infrasound from windturbines does not exceed the human sensory threshold, it cannot be completely ignored since it may
influence the vestibular system, and thus health effects other than sleep disorder also need to bereviewed.
The visibility of wind turbines and attitudes towards scenic views were identified as cofounding
factors in previous studies, but no statistically significant effects were found in this study. In thesurveyed area, attitudes toward accepting wind power generation were favorable compared to theareas in previous studies; this may have influenced the outcome, and therefore analyses are neededthat take into account the characteristics of each area. Of the cofounding factors considered in thisstudy, “attitude towards wind power generation facilities (past, present)” was most strongly
associated with sleep disorder, increasing its likelihood by approximately fivefold. Sub -analysis ofparticipants with a favorable current attitude towards wind turbines (n = 879) showed that annoyancewith wind turbine noise was significantly related to distance from the wind turbine (data not shown);
however, there was no significant relationship between distance and sleep disorder, and therefore it
seems important to determine how to build consensus prior to introducing new wind power
generation facilities. The Ministry of the Environment created a report called “Dealing with noise
generated from wind power generation facilities” that points out the importance of promoting
communication between stakeholders.
The limitations of this study are as follows. The collection rate of questionnaires was only 28.3%,
which is low, and therefore although we confirmed that the overall population and a sample did not
differ in the distribution of gender and age, the validity of the data remains to be verified. The
distance from the nearest wind turbine was calculated from the location of the local public city hallto which each respondent belonged, rather than from each respondent’s actual residence. This may
have led to inaccuracy regarding distance information. For the estimation of the wind turbine
A-weighted equivalent continuous sound level (L Aeq), a distance attenuation curve <L Aeq,WTN(d) =-20.9log 10 d + 87.9, where d is a distance (m)> was derived based on the measurements obtained atnine locations where wind power generation facilities were visible. These consisted of five locations
in area A, with horizontal distances to the wind turbine from 337 m to 1,485 m, and four locations inarea B, with distances from 944 m to 1,766 m. The validity of the estimation equation is not fully
confirmed. Finally, this epidemiological research design was cross-sectional in nature, and therefore
it cannot be used to determine any causal relationship between exposure to noise (cause) and healtheffects (result). Only the possibilities of such relationships can be identified. Longitudinal studies(cohort studies) involving wind turbine noise and health effects are rare worldwide, but these arenecessary to prove causal relationships.
In Japan, based on situations involving noise complaints, the Minis try of the Environment
generally defines low-frequency noise as 100 Hz or lower. Internationally, the definition of
low-frequency noise differs by country and no standard exists. The International Electro -technicalCommission (IEC) standard 61400 series defines infrasound as 20 Hz or lower, and low-frequency
noise as 20 to 100 Hz. In Japan, the Japan Industrial Standard (JIS) uses the same definition as theIEC. Japanese environmental assessment law defines noise (frequency 20 to 100 Hz) and infrasound(frequency 20 Hz and lower), and does not use the term “low-frequency noise.” Generally, in termsof wind turbine noise concerns, many residents worry about the health effects of so -called“low-frequency noise,” defined as 100 Hz and below, but they also do no t realize that low-frequency
noise (infrasound) is inaudible. In the future, public awareness campaigns about the proper usage of1461

the term “low-frequency noise” are necessary not only for researchers but also for businessdevelopers and local residents. These campaigns will increase mutual understanding and the sharingof measurement results, and promote the development of new strategies regarding wind turbine
noise.

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