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The relationship between noise annoyance and salivary cortisol
Applied Acoustics 160 (2020) 107131
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Applied Acoustics journal homepage: www.elsevier.com/locate/apacoust
The relationship between noise annoyance and salivary cortisol Khadijeh Yaghoubi a, Iraj Alimohammadi b,⇑, Jamileh Abolghasemi c, Mehdi Shirin Shandiz d, Nahid Aboutaleb e, Hossein Ebrahimi f a
School of Public Health, Iran University of Medical Sciences, Tehran, Iran Research Center of Occupational Health, School of Public Health, Iran University of Medical Sciences, Tehran, Iran c Department of Biostatistics, School of Public Health, Iran University of Medical Sciences, Tehran, Iran d School of Medicine, Zahedan University of Medical Sciences, Iran e School of Medicine, Iran University of Medical Sciences, Tehran, Iran f Air Pollution Research Center, School of Public Health, Iran University of Medical Sciences, Tehran, Iran b
a r t i c l e
i n f o
Article history: Received 3 August 2019 Received in revised form 21 October 2019 Accepted 1 November 2019
Keywords: Noise Noise annoyance Cortisol Stress
a b s t r a c t The noise exposure causes the secretion of different stress hormones, including cortisol. Since noise annoyance does not depend just on the level of noise, the main objective of this study was to examine the relationship between noise annoyance and salivary cortisol levels based on individual variables. 78 individuals from a car manufacturing company participated in this study which include two experimental groups (The first group was exposed to 75–85 dBA and the second to 85–95 dBA noise levels) and control group (the individuals in this group were exposed to 60–70 dBA noise levels). Saliva samples were taken once in the morning (6:30–7) and once in the afternoon (12–12:30) which were analyzed using IBL ELISA test kits. The degree of annoyance was measured using a noise annoyance questionnaire. The result shows that there was a significant relationship between cortisol level and work experience at the end of the work shift (P = 0.021). Also, there was a significant difference between the mean cortisol level at the beginning of the shift (15.50 mg per liter) and at the end of it (10.97 mg per liter) (P = 0.000). The study results showed that salivary cortisol levels were not significantly related to the annoyance level at the beginning of the shift (P = 0.942), but is significantly related to the level of noise annoyance at the end of the shift (P = 0.006). This study shows that there is a significant relationship between annoyance and cortisol secretion level after noise exposure. Ó 2019 Elsevier Ltd. All rights reserved.
1. Introduction The process of industrialization and urbanization is bringing about increases in noise pollution and in the number of exposed people every day. 600 million workers are exposed to occupational noise worldwide [1,2]. In the United States, about 9 million people are exposed to noise levels above 85 dBA [3]. Noise health effects can be divided into two categories, auditory and non-auditory effects [4]. Auditory effects include hearing impairment and tinnitus. Non-auditory effects, which are not directly related to sound energy, include work productivity and activity impairment, sleep disturbance, physiological responses, and noise annoyance [5]. Noise annoyance is a feeling of displeasure, nuisance, or irritation, which adversely affects a person or groups of persons [6–8]. It can also be defined as noise overall unwantedness [9]. According to experts, the concept of noise annoyance has a wide range of ⇑ Corresponding author. E-mail address: [email protected] (I. Alimohammadi). https://doi.org/10.1016/j.apacoust.2019.107131 0003-682X/Ó 2019 Elsevier Ltd. All rights reserved.
understanding. Annoyance can be defined as an emotion, attitude or knowledge, or as a result of disturbance, or rational decision [10]. It has been estimated that 30% of the European Union’s population is suffering from noise annoyance [11]. Previous studies suggest that noise annoyance is affected by non-acoustic factors, including individual traits and attitudes, as well as acoustic factors, including sound level and frequency spectrum [6,12,13]. Noise annoyance is often related to noise interference with everyday activities [8,14]. Overall, it is believed that noise leads to the activity and communication disorders, and thereby causes annoyance [4,5]. Relatively numerous studies have examined the effect of noise on the secretion of stress hormones. Most of these studies have indicated that exposure to intense industrial noise can lead to increased noradrenaline and adrenaline levels [15–17]. The physiological effects of noise are related to increased activity of the hypothalamic-pituitaryadrenal (HPA) neuroendocrine system [18]. Cortisol is the most important HPA axis hormone. It regulates carbohydrate and lipid metabolism as well as the immune
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K. Yaghoubi et al. / Applied Acoustics 160 (2020) 107131
system of the body and has a significant impact on mood and cognitive processes [18–20]. Moreover, everyday stress has also been proven to increase cortisol levels [21,22]. Cortisol is a reliable indicator of stress. The effects of long-term elevated cortisol on the HPA axis can be manifested as insulin resistance, intestinal disorders, cardiovascular diseases, and sleep disturbance [4,23]. Some studies have revealed that increased cortisol is related to noise [24,25]. The general pattern of endocrine responses to noise is indicative of noise as a stressor, exciting short-term physiological responses; however, there are inconsistencies among studies [4]. Various studies have been conducted on the effect of lowfrequency noise on salivary cortisol concentrations. Waye et al. (2002) studied the concentration of salivary cortisol in an environment with low-frequency noise and concluded that cortisol was affected by stress and noise exposure during work performance [18]. Hebert et al. (2009) examined the effects of lowfrequency noise on cortisol level and mental stress in people with tinnitus disorder and reported changes in cortisol levels [26]. Melamed (1996) measured urinary cortisol concentration among 35 workers exposed to 85 dBA industrial noise and found the increased urine cortisol excretion after exposure [23]. Selander examined the effect of aircraft noise on salivary cortisol levels of men at noise levels between 50 and 60 dBA but found no significant relationship [27]. The association between long-term and short-term noise exposure with cortisol levels was studied among 398 service, industry, and financial workers in 2013, and no statistically significant relationship was found [28]. The study of the relationship between noise annoyance and physiological responses can be particularly important. Some studies have examined the association of noise annoyance with stress responses, symptoms, and illness [4,29]. Some studies have shown that noise exposure triggers a number of short-term physiological responses, such as increased heart rate and blood pressure, peripheral vasoconstriction, and increased peripheral vascular resistance [30–32]. It is likely that noise affects blood pressure through an intermediate response, such as noise annoyance; although this hypothesis has not been conclusively proved [4]. The results of a meta-analysis revealed a positive and significant relationship between the annoyance from road traffic noise and the risk of arterial hypertension [33]. The main objective of this study was to examine the relationship between noise annoyance and salivary cortisol levels based on individual variables. Research has shown that noise causes the secretion of different stress hormones, including cortisol. Since noise annoyance does not depend just on the level of noise [34], the question arose to the authors if there is a significant relationship between noise annoyance, as a noise dependent variable, and cortisol secretion level. If noise annoyance is proved to be significantly related to increased cortisol secretion, it can be concluded that noise annoyance is the indicator and inductor of physiological and physical side effects in individuals.
2. Materials and methods This research was carried out in the assembly and warehouse units of a car manufacturing company. The two experimental groups were selected from the assembly unit (The first group was exposed to 75–85 dBA and the second to 85–95 dBA noise levels). The control group was selected from the warehouse unit (the individuals in this group were exposed to 60–70 dBA noise levels). The sample size of each group was 26, which were selected randomly. The total number of participants in the study was 78. The noise measurement was performed according to the ISO standard [35] by a B&K 2337 sound level meter.
The employees in three different units (two assembly units and a warehouse unit) were invited to participate in the study. The medical records of the volunteers were reviewed at the occupational medicine unit. Individuals with cardiovascular diseases, diabetes, renal and psychiatric disorders, and hearing loss, or those who took specific medications were excluded. The study subjects were provided with detailed explanations about the goals of the study and how it was carried out. Then they were asked to complete the consent form. Subjects were banned from eating, drinking, and smoking one hour before providing the saliva sample. They were also asked not to use hearing protection headphones on the day of giving the samples. Their height and weight were measured to calculate their body mass index (BMI). Saliva samples were taken once in the morning (6:30–7) and once in the afternoon (12–12:30). Two ccs of samples were collected in 5 cc-tubes containing sterile cotton. The tubes were then sealed with paraffin and transferred to the lab. Saliva collection was carried out in the assembly and warehouse units and was repeated within ten days. Samples were centrifuged in the laboratory and then frozen at 25 °C. All samples were analyzed using IBL ELISA test kits. After noise exposure, the degree of annoyance was measured using a noise annoyance questionnaire [36]. Annoyance level was determined by two numerical scales, ranging from 1 to 11, and a verbal scale, ranging from no-annoyance to a high level of annoyance. Noise annoyance was measured at the end of work shift (after exposure to noise). A general questionnaire was also used to determine individual information. The Kolmogorov-Smirnov test was performed to determine the normality of the data. Since all data were normal, the ANOVA test was used to compare the workers’ age and body mass index at different noise levels. Post Hoc test was used to compare the two groups. Finally, a multiple linear regression was used to determine the relationship between cortisol levels and the study variables. In order to perform the linear regression, the normality of the data was first verified and confirmed. Then, the correlation between variables was evaluated using the Pearson correlation coefficient, independent t-test, and ANOVA at 0.2 error level. 3. Results This study was conducted on 78 employees in three units of a car manufacturing company. The number of subjects included in the study was 26 per selected unit. The mean age, work experience, cortisol and annoyance levels are presented in Table 1. Individuals in the assembly unit (the groups exposed to higher noise levels) were more annoyed as compared to those in the warehouse unit (the control group) (Table 1). In other words, the annoyance degree increased with an increase in noise level. As indicated in Table 1, there is no significant difference between salivary cortisol in the morning and afternoon at different noise levels. The correlation coefficient between the variables showed that there was a significant relationship between cortisol level and work experience at the end of the work shift. (Table 2) (P = 0.021). Also, there was a significant difference between the mean cortisol level at the beginning of the shift (15.50 mg per liter) and at the end of it (10.97 mg per liter) (P = 0.000) (Table 2). The study results showed that salivary cortisol levels were not significantly related to the annoyance level at the beginning of the shift (P = 0.942). As shown in Table 3, the salivary cortisol level is significantly related to the level of noise annoyance at the end of the shift; in other words, salivary cortisol levels increases with an increase in annoyance level (P = 0.006). Among the study variables, experience and annoyance were candidates to enter multiple linear regressions. Finally, the regression line was calculated as follows.
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K. Yaghoubi et al. / Applied Acoustics 160 (2020) 107131 Table 1 The mean and standard deviation of age, work experience, cortisol and annoyance levels. Age (years)
Experience (Years)
Groups
Mean (SD)
P-value
Mean (SD)
P-value
60–70 (control)
38.38 (±0.94)
0.549
11.42 (±0.97)
0.024
75–85 (case)
38.88 (±1.34)
85–95 (case) Total
Cortisol level
Annoyance
Mean (SD)
P-value
(frequency)
P-value
Morning Evening
15.85 (±0.45) 15.20 (±0.25)
0.715 (Morning) 0.512 (Evening)
0.013
12.82 (±0.98)
Morning Evening
15.37 (±0.55) 15.75 (±0.33)
37.03 (±1.34)
9.19 (±0.8)
Morning Evening
15.37 (±0.43) 15.47 (±0.19)
38.10 (±0.70)
11.08 (±0.55)
Morning Evening
15.53 (±0.28) 15.47 (±0.26)
L:7 M:9 H:10 L:1 M:7 H:18 M:3 H:23 78
Table 2 The correlation between morning and evening cortisol levels and the study variables. Morning cortisol Morning cortisol Evening cortisol
Evening cortisol
1 r = 0.477 P = 0.000 r = 0.064 P = 0.575 r = 0.055 P = 0.642
Age Experience
Age
Experience
1 r = 0.196 P = 0.085 r = 0.266 P = 0.021
1 r = 0.482 P = 0.000
1
Table 3 A comparison between annoyance levels based on the study variables. Variables
Low annoyance Mean (SD)
Medium annoyance Mean (SD)
High annoyance Mean (SD)
Mean (SD) Mean (SD)
Test statistic F (degree of freedom)
Sign P-value
Morning cortisol Evening cortisol Age Experience
15.65 (±0.51) 8.95 (±0.44) 40.12 (±2.13) 11.89 (±1.50)
15.40 10.23 37.63 11.58
15.51 (±0.25) 11.55 (±0.33) 37.96 (±0.87) 9.35 (±0.68)
15.50 (±1.75) 15.47(±0.26) 38.10 (±6.23) 11.08 (±0.55)
0.060 5.421 0.482 1.379
0.942 0.006 0.619 0.280
(±0.38) (±0.58) (±1.45) (±2.99)
Cortisol lev e at end of work shift ¼ 10:642 þ 1:027medium annoyed þ 2:237highly annoyed 0:126experience
ð1Þ
This study shows that there is a significant relationship between annoyance and cortisol secretion level after noise exposure (Eq. (1), Table 3). Eqs. (2)–(4) show the cortisol secretion level based on the degree of annoyance at the shift end. As is clear, the only effective independent variable is the work experience. Age has no impact on the relationship between annoyance and cortisol secretion.
cortisol lev el in low annoyed ¼ 10:642 0:126experience
ð2Þ
cortisol lev el in medium annoyed ¼ 11:669 0:126experience cortisol lev el in highly annoyed ¼ 12:879 0:126experience
ð3Þ ð4Þ
4. Discussion The present study shows that salivary cortisol levels increase with an increase in noise annoyance. Various studies have explored the relationship between noise and stress hormone secretion, but as far as the authors know, no study has investigated the relationship between noise annoyance and salivary cortisol. A relatively large number of studies have confirmed the association between noise and cortisol [24,37], but the relationship between noise
(2.75) (2.75) (2.75) (2.16)
annoyance and cortisol, as an indicator of stress, has not been studied. Studies conducted so far have reported that chronic noise exposure increases cortisol levels, together with increased fatigue and irritability, at the end of a work shift [23]. Findings have proven the net contribution of environmental noise to elevating stress responses in everyday activities [23]. Many physiological processes vary in response to environmental stress. For example, environmental stressors can lead to the production of stress-related hormones. The secretion of these hormones allows the body to maintain more energy to adapt to increased demand [24]. Studies conducted on the effects of noise on stress hormones have more focused on urine, blood, and adrenaline and noradrenaline hormones. However, salivary cortisol has been recently recognized as a useful diagnostic tool to study the physiological effects of noise on stress [38]). Stahl & Dorner 1982 have shown that cortisol level would increase several times following stimulation [39]. Based on previous research, using saliva for cortisol measurement is a simple, non-invasive, and reliable way to evaluate the free cortisol levels in the blood [24,38]. Research has revealed that measurement of salivary cortisol throughout the day should be performed based on the morning wake-up time [40]. In this study, the measurement of cortisol in the saliva is an advantage, as it prevents the stress caused by blood sampling. Many studies have shown that only 10–20 percent of noise annoyance is related to noise exposure [34]. Fields (1993) and Job (1988) have shown that personality traits play an important role in causing annoyance. Besides, there is a high potential for oxidative stress, and this depends on how noise is interpreted in the central nervous system [41,42]. Noise annoyance depends to
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a greater degree on the noise meaning and its predictability, and to a lesser degree on the noise level [43]. Also, various studies have shown that annoyance has a dose-response relationship with noise exposure. Therefore, it can be concluded that the relationship between cortisol level and annoyance depends not only on the noise level but on other parameters affecting annoyance, including non-acoustic ones [8]. The results of this study indicate that significant changes in the mean difference of the morning and afternoon cortisol levels are due to individual annoyance levels, and psychosocial factors only play a minor role [40]. Stokes & Kite (2001) proposed that there are two traditional models of psychological stress: the stimulusbased and the response-based models [44]. The response-based approach defines stress as the human response to a stressor [45]. Based on this approach, noise annoyance can be considered as a kind of stress since it is caused by human exposure to noise, although many factors affect its intensity. The word stress is associated with a large number of different constructs, such as anxiety, arousal, coping, strain, and tension [46]. Stokes & Kite (2001) suggest that noise annoyance can be considered as stress, although physiological measures failed to provide an understanding of the human stress response [44]. It is well known that cortisol is related to important health parameters including stress and effects on the immune system [47]. Waye et al. (2002) suggested that changes in cortisol levels affect human health. They reported that noise annoyance imposes an allosteric load on the body, which chronically increases the activity of HPA (hypothalamus pituitary adrenal) axis [18]. Increased HPA activity leads to the onset or worsening of symptoms related to such diseases as osteoporosis, coronary heart disease, hypertension, diabetes, and diseases related to the immune system [48]. It has also been shown that cortisol secretion would cause stress ulcer, protein degradation, reducing the synthesis of muscle protein, and increasing level of glucose in the blood, and Immunosuppression [49]. 5. Conclusion The results of this study suggest that noise annoyance changes human cortisol levels so that the greater the degree of annoyance, the higher the cortisol level. Besides, these results indicate that the continuation of noise annoyance leads to more cortisol secretion in exposed subjects. Therefore, it can be concluded that there is a significant relationship between noise annoyance and stress. The present study showed that there was a direct and positive relationship between noise annoyance and cortisol secretion. Considering the effects of cortisol hypersecretion on the human body, it can be concluded that noise annoyance is an indicator of physical side effects in individuals. Further studies are recommended in this regard. Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper. Acknowledgements The authors would like to thank all colleagues for help in this project. Funding This work was supported by Iran university of Medical Sciences [grant number 25326, 2016].
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Contents lists available at ScienceDirect
Applied Acoustics journal homepage: www.elsevier.com/locate/apacoust
The relationship between noise annoyance and salivary cortisol Khadijeh Yaghoubi a, Iraj Alimohammadi b,⇑, Jamileh Abolghasemi c, Mehdi Shirin Shandiz d, Nahid Aboutaleb e, Hossein Ebrahimi f a
School of Public Health, Iran University of Medical Sciences, Tehran, Iran Research Center of Occupational Health, School of Public Health, Iran University of Medical Sciences, Tehran, Iran c Department of Biostatistics, School of Public Health, Iran University of Medical Sciences, Tehran, Iran d School of Medicine, Zahedan University of Medical Sciences, Iran e School of Medicine, Iran University of Medical Sciences, Tehran, Iran f Air Pollution Research Center, School of Public Health, Iran University of Medical Sciences, Tehran, Iran b
a r t i c l e
i n f o
Article history: Received 3 August 2019 Received in revised form 21 October 2019 Accepted 1 November 2019
Keywords: Noise Noise annoyance Cortisol Stress
a b s t r a c t The noise exposure causes the secretion of different stress hormones, including cortisol. Since noise annoyance does not depend just on the level of noise, the main objective of this study was to examine the relationship between noise annoyance and salivary cortisol levels based on individual variables. 78 individuals from a car manufacturing company participated in this study which include two experimental groups (The first group was exposed to 75–85 dBA and the second to 85–95 dBA noise levels) and control group (the individuals in this group were exposed to 60–70 dBA noise levels). Saliva samples were taken once in the morning (6:30–7) and once in the afternoon (12–12:30) which were analyzed using IBL ELISA test kits. The degree of annoyance was measured using a noise annoyance questionnaire. The result shows that there was a significant relationship between cortisol level and work experience at the end of the work shift (P = 0.021). Also, there was a significant difference between the mean cortisol level at the beginning of the shift (15.50 mg per liter) and at the end of it (10.97 mg per liter) (P = 0.000). The study results showed that salivary cortisol levels were not significantly related to the annoyance level at the beginning of the shift (P = 0.942), but is significantly related to the level of noise annoyance at the end of the shift (P = 0.006). This study shows that there is a significant relationship between annoyance and cortisol secretion level after noise exposure. Ó 2019 Elsevier Ltd. All rights reserved.
1. Introduction The process of industrialization and urbanization is bringing about increases in noise pollution and in the number of exposed people every day. 600 million workers are exposed to occupational noise worldwide [1,2]. In the United States, about 9 million people are exposed to noise levels above 85 dBA [3]. Noise health effects can be divided into two categories, auditory and non-auditory effects [4]. Auditory effects include hearing impairment and tinnitus. Non-auditory effects, which are not directly related to sound energy, include work productivity and activity impairment, sleep disturbance, physiological responses, and noise annoyance [5]. Noise annoyance is a feeling of displeasure, nuisance, or irritation, which adversely affects a person or groups of persons [6–8]. It can also be defined as noise overall unwantedness [9]. According to experts, the concept of noise annoyance has a wide range of ⇑ Corresponding author. E-mail address: [email protected] (I. Alimohammadi). https://doi.org/10.1016/j.apacoust.2019.107131 0003-682X/Ó 2019 Elsevier Ltd. All rights reserved.
understanding. Annoyance can be defined as an emotion, attitude or knowledge, or as a result of disturbance, or rational decision [10]. It has been estimated that 30% of the European Union’s population is suffering from noise annoyance [11]. Previous studies suggest that noise annoyance is affected by non-acoustic factors, including individual traits and attitudes, as well as acoustic factors, including sound level and frequency spectrum [6,12,13]. Noise annoyance is often related to noise interference with everyday activities [8,14]. Overall, it is believed that noise leads to the activity and communication disorders, and thereby causes annoyance [4,5]. Relatively numerous studies have examined the effect of noise on the secretion of stress hormones. Most of these studies have indicated that exposure to intense industrial noise can lead to increased noradrenaline and adrenaline levels [15–17]. The physiological effects of noise are related to increased activity of the hypothalamic-pituitaryadrenal (HPA) neuroendocrine system [18]. Cortisol is the most important HPA axis hormone. It regulates carbohydrate and lipid metabolism as well as the immune
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system of the body and has a significant impact on mood and cognitive processes [18–20]. Moreover, everyday stress has also been proven to increase cortisol levels [21,22]. Cortisol is a reliable indicator of stress. The effects of long-term elevated cortisol on the HPA axis can be manifested as insulin resistance, intestinal disorders, cardiovascular diseases, and sleep disturbance [4,23]. Some studies have revealed that increased cortisol is related to noise [24,25]. The general pattern of endocrine responses to noise is indicative of noise as a stressor, exciting short-term physiological responses; however, there are inconsistencies among studies [4]. Various studies have been conducted on the effect of lowfrequency noise on salivary cortisol concentrations. Waye et al. (2002) studied the concentration of salivary cortisol in an environment with low-frequency noise and concluded that cortisol was affected by stress and noise exposure during work performance [18]. Hebert et al. (2009) examined the effects of lowfrequency noise on cortisol level and mental stress in people with tinnitus disorder and reported changes in cortisol levels [26]. Melamed (1996) measured urinary cortisol concentration among 35 workers exposed to 85 dBA industrial noise and found the increased urine cortisol excretion after exposure [23]. Selander examined the effect of aircraft noise on salivary cortisol levels of men at noise levels between 50 and 60 dBA but found no significant relationship [27]. The association between long-term and short-term noise exposure with cortisol levels was studied among 398 service, industry, and financial workers in 2013, and no statistically significant relationship was found [28]. The study of the relationship between noise annoyance and physiological responses can be particularly important. Some studies have examined the association of noise annoyance with stress responses, symptoms, and illness [4,29]. Some studies have shown that noise exposure triggers a number of short-term physiological responses, such as increased heart rate and blood pressure, peripheral vasoconstriction, and increased peripheral vascular resistance [30–32]. It is likely that noise affects blood pressure through an intermediate response, such as noise annoyance; although this hypothesis has not been conclusively proved [4]. The results of a meta-analysis revealed a positive and significant relationship between the annoyance from road traffic noise and the risk of arterial hypertension [33]. The main objective of this study was to examine the relationship between noise annoyance and salivary cortisol levels based on individual variables. Research has shown that noise causes the secretion of different stress hormones, including cortisol. Since noise annoyance does not depend just on the level of noise [34], the question arose to the authors if there is a significant relationship between noise annoyance, as a noise dependent variable, and cortisol secretion level. If noise annoyance is proved to be significantly related to increased cortisol secretion, it can be concluded that noise annoyance is the indicator and inductor of physiological and physical side effects in individuals.
2. Materials and methods This research was carried out in the assembly and warehouse units of a car manufacturing company. The two experimental groups were selected from the assembly unit (The first group was exposed to 75–85 dBA and the second to 85–95 dBA noise levels). The control group was selected from the warehouse unit (the individuals in this group were exposed to 60–70 dBA noise levels). The sample size of each group was 26, which were selected randomly. The total number of participants in the study was 78. The noise measurement was performed according to the ISO standard [35] by a B&K 2337 sound level meter.
The employees in three different units (two assembly units and a warehouse unit) were invited to participate in the study. The medical records of the volunteers were reviewed at the occupational medicine unit. Individuals with cardiovascular diseases, diabetes, renal and psychiatric disorders, and hearing loss, or those who took specific medications were excluded. The study subjects were provided with detailed explanations about the goals of the study and how it was carried out. Then they were asked to complete the consent form. Subjects were banned from eating, drinking, and smoking one hour before providing the saliva sample. They were also asked not to use hearing protection headphones on the day of giving the samples. Their height and weight were measured to calculate their body mass index (BMI). Saliva samples were taken once in the morning (6:30–7) and once in the afternoon (12–12:30). Two ccs of samples were collected in 5 cc-tubes containing sterile cotton. The tubes were then sealed with paraffin and transferred to the lab. Saliva collection was carried out in the assembly and warehouse units and was repeated within ten days. Samples were centrifuged in the laboratory and then frozen at 25 °C. All samples were analyzed using IBL ELISA test kits. After noise exposure, the degree of annoyance was measured using a noise annoyance questionnaire [36]. Annoyance level was determined by two numerical scales, ranging from 1 to 11, and a verbal scale, ranging from no-annoyance to a high level of annoyance. Noise annoyance was measured at the end of work shift (after exposure to noise). A general questionnaire was also used to determine individual information. The Kolmogorov-Smirnov test was performed to determine the normality of the data. Since all data were normal, the ANOVA test was used to compare the workers’ age and body mass index at different noise levels. Post Hoc test was used to compare the two groups. Finally, a multiple linear regression was used to determine the relationship between cortisol levels and the study variables. In order to perform the linear regression, the normality of the data was first verified and confirmed. Then, the correlation between variables was evaluated using the Pearson correlation coefficient, independent t-test, and ANOVA at 0.2 error level. 3. Results This study was conducted on 78 employees in three units of a car manufacturing company. The number of subjects included in the study was 26 per selected unit. The mean age, work experience, cortisol and annoyance levels are presented in Table 1. Individuals in the assembly unit (the groups exposed to higher noise levels) were more annoyed as compared to those in the warehouse unit (the control group) (Table 1). In other words, the annoyance degree increased with an increase in noise level. As indicated in Table 1, there is no significant difference between salivary cortisol in the morning and afternoon at different noise levels. The correlation coefficient between the variables showed that there was a significant relationship between cortisol level and work experience at the end of the work shift. (Table 2) (P = 0.021). Also, there was a significant difference between the mean cortisol level at the beginning of the shift (15.50 mg per liter) and at the end of it (10.97 mg per liter) (P = 0.000) (Table 2). The study results showed that salivary cortisol levels were not significantly related to the annoyance level at the beginning of the shift (P = 0.942). As shown in Table 3, the salivary cortisol level is significantly related to the level of noise annoyance at the end of the shift; in other words, salivary cortisol levels increases with an increase in annoyance level (P = 0.006). Among the study variables, experience and annoyance were candidates to enter multiple linear regressions. Finally, the regression line was calculated as follows.
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K. Yaghoubi et al. / Applied Acoustics 160 (2020) 107131 Table 1 The mean and standard deviation of age, work experience, cortisol and annoyance levels. Age (years)
Experience (Years)
Groups
Mean (SD)
P-value
Mean (SD)
P-value
60–70 (control)
38.38 (±0.94)
0.549
11.42 (±0.97)
0.024
75–85 (case)
38.88 (±1.34)
85–95 (case) Total
Cortisol level
Annoyance
Mean (SD)
P-value
(frequency)
P-value
Morning Evening
15.85 (±0.45) 15.20 (±0.25)
0.715 (Morning) 0.512 (Evening)
0.013
12.82 (±0.98)
Morning Evening
15.37 (±0.55) 15.75 (±0.33)
37.03 (±1.34)
9.19 (±0.8)
Morning Evening
15.37 (±0.43) 15.47 (±0.19)
38.10 (±0.70)
11.08 (±0.55)
Morning Evening
15.53 (±0.28) 15.47 (±0.26)
L:7 M:9 H:10 L:1 M:7 H:18 M:3 H:23 78
Table 2 The correlation between morning and evening cortisol levels and the study variables. Morning cortisol Morning cortisol Evening cortisol
Evening cortisol
1 r = 0.477 P = 0.000 r = 0.064 P = 0.575 r = 0.055 P = 0.642
Age Experience
Age
Experience
1 r = 0.196 P = 0.085 r = 0.266 P = 0.021
1 r = 0.482 P = 0.000
1
Table 3 A comparison between annoyance levels based on the study variables. Variables
Low annoyance Mean (SD)
Medium annoyance Mean (SD)
High annoyance Mean (SD)
Mean (SD) Mean (SD)
Test statistic F (degree of freedom)
Sign P-value
Morning cortisol Evening cortisol Age Experience
15.65 (±0.51) 8.95 (±0.44) 40.12 (±2.13) 11.89 (±1.50)
15.40 10.23 37.63 11.58
15.51 (±0.25) 11.55 (±0.33) 37.96 (±0.87) 9.35 (±0.68)
15.50 (±1.75) 15.47(±0.26) 38.10 (±6.23) 11.08 (±0.55)
0.060 5.421 0.482 1.379
0.942 0.006 0.619 0.280
(±0.38) (±0.58) (±1.45) (±2.99)
Cortisol lev e at end of work shift ¼ 10:642 þ 1:027medium annoyed þ 2:237highly annoyed 0:126experience
ð1Þ
This study shows that there is a significant relationship between annoyance and cortisol secretion level after noise exposure (Eq. (1), Table 3). Eqs. (2)–(4) show the cortisol secretion level based on the degree of annoyance at the shift end. As is clear, the only effective independent variable is the work experience. Age has no impact on the relationship between annoyance and cortisol secretion.
cortisol lev el in low annoyed ¼ 10:642 0:126experience
ð2Þ
cortisol lev el in medium annoyed ¼ 11:669 0:126experience cortisol lev el in highly annoyed ¼ 12:879 0:126experience
ð3Þ ð4Þ
4. Discussion The present study shows that salivary cortisol levels increase with an increase in noise annoyance. Various studies have explored the relationship between noise and stress hormone secretion, but as far as the authors know, no study has investigated the relationship between noise annoyance and salivary cortisol. A relatively large number of studies have confirmed the association between noise and cortisol [24,37], but the relationship between noise
(2.75) (2.75) (2.75) (2.16)
annoyance and cortisol, as an indicator of stress, has not been studied. Studies conducted so far have reported that chronic noise exposure increases cortisol levels, together with increased fatigue and irritability, at the end of a work shift [23]. Findings have proven the net contribution of environmental noise to elevating stress responses in everyday activities [23]. Many physiological processes vary in response to environmental stress. For example, environmental stressors can lead to the production of stress-related hormones. The secretion of these hormones allows the body to maintain more energy to adapt to increased demand [24]. Studies conducted on the effects of noise on stress hormones have more focused on urine, blood, and adrenaline and noradrenaline hormones. However, salivary cortisol has been recently recognized as a useful diagnostic tool to study the physiological effects of noise on stress [38]). Stahl & Dorner 1982 have shown that cortisol level would increase several times following stimulation [39]. Based on previous research, using saliva for cortisol measurement is a simple, non-invasive, and reliable way to evaluate the free cortisol levels in the blood [24,38]. Research has revealed that measurement of salivary cortisol throughout the day should be performed based on the morning wake-up time [40]. In this study, the measurement of cortisol in the saliva is an advantage, as it prevents the stress caused by blood sampling. Many studies have shown that only 10–20 percent of noise annoyance is related to noise exposure [34]. Fields (1993) and Job (1988) have shown that personality traits play an important role in causing annoyance. Besides, there is a high potential for oxidative stress, and this depends on how noise is interpreted in the central nervous system [41,42]. Noise annoyance depends to
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a greater degree on the noise meaning and its predictability, and to a lesser degree on the noise level [43]. Also, various studies have shown that annoyance has a dose-response relationship with noise exposure. Therefore, it can be concluded that the relationship between cortisol level and annoyance depends not only on the noise level but on other parameters affecting annoyance, including non-acoustic ones [8]. The results of this study indicate that significant changes in the mean difference of the morning and afternoon cortisol levels are due to individual annoyance levels, and psychosocial factors only play a minor role [40]. Stokes & Kite (2001) proposed that there are two traditional models of psychological stress: the stimulusbased and the response-based models [44]. The response-based approach defines stress as the human response to a stressor [45]. Based on this approach, noise annoyance can be considered as a kind of stress since it is caused by human exposure to noise, although many factors affect its intensity. The word stress is associated with a large number of different constructs, such as anxiety, arousal, coping, strain, and tension [46]. Stokes & Kite (2001) suggest that noise annoyance can be considered as stress, although physiological measures failed to provide an understanding of the human stress response [44]. It is well known that cortisol is related to important health parameters including stress and effects on the immune system [47]. Waye et al. (2002) suggested that changes in cortisol levels affect human health. They reported that noise annoyance imposes an allosteric load on the body, which chronically increases the activity of HPA (hypothalamus pituitary adrenal) axis [18]. Increased HPA activity leads to the onset or worsening of symptoms related to such diseases as osteoporosis, coronary heart disease, hypertension, diabetes, and diseases related to the immune system [48]. It has also been shown that cortisol secretion would cause stress ulcer, protein degradation, reducing the synthesis of muscle protein, and increasing level of glucose in the blood, and Immunosuppression [49]. 5. Conclusion The results of this study suggest that noise annoyance changes human cortisol levels so that the greater the degree of annoyance, the higher the cortisol level. Besides, these results indicate that the continuation of noise annoyance leads to more cortisol secretion in exposed subjects. Therefore, it can be concluded that there is a significant relationship between noise annoyance and stress. The present study showed that there was a direct and positive relationship between noise annoyance and cortisol secretion. Considering the effects of cortisol hypersecretion on the human body, it can be concluded that noise annoyance is an indicator of physical side effects in individuals. Further studies are recommended in this regard. Declaration of Competing Interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper. Acknowledgements The authors would like to thank all colleagues for help in this project. Funding This work was supported by Iran university of Medical Sciences [grant number 25326, 2016].
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