Hearing risk associated with the usage of personal listening devices among urban high school students in Malaysia

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Original Research

Hearing risk associated with the usage of personal listening devices among urban high school students in Malaysia

A.H. Sulaiman, K. Seluakumaran*, R. Husain

Department of Physiology, Faculty of Medicine, University of Malaya, 50603 Kuala Lumpur, Wilayah Persekutuan, Malaysia

a r t i c l e i n f o

Article history:

Received 3 August 2012 Received in revised form 1 November 2012 Accepted 7 January 2013 Available online 7 March 2013

Keywords:

Noise-induced hearing loss Adolescents

Personal listening devices Mp3 players

High-frequency audiometry High school students

a b s t r a c t

Objectives:To investigate listening habits and hearing risks associated with the use of personal listening devices among urban high school students in Malaysia.

Study design:Cross-sectional, descriptive study.

Methods:In total, 177 personal listening device users (13e16 years old) were interviewed to elicit their listening habits (e.g. listening duration, volume setting) and symptoms of hearing loss. Their listening levels were also determined by asking them to set their usual listening volume on an Apple iPod TM playing a pre-selected song. The iPod’s sound output was measured with an artificial ear connected to a sound level meter. Subjects also underwent pure tone audiometry to ascertain their hearing thresholds at standard frequencies (0.5 e8 kHz) and extended high frequencies (9e16 kHz).

Results:The mean measured listening level and listening duration for all subjects were 72.2 dBA and 1.2 h/day, respectively. Their self-reported listening levels were highly correlated with the measured levels (P<0.001). Subjects who listened at higher volumes also tend to listen for longer durations (P ¼0.012). Male subjects listened at a significantly higher volume than female subjects (P¼0.008). When sound exposure levels were compared with the recommended occupational noise exposure limit, 4.5% of subjects were found to be listening at levels which require mandatory hearing protection in the occupational setting. Hearing loss (25 dB hearing level at one or more standard test frequencies) was detected in 7.3% of subjects. Subjects’ sound exposure levels from the devices were positively correlated with their hearing thresholds at two of the extended high frequencies (11.2 and 14 kHz), which could indicate an early stage of noise-induced hearing loss.

Conclusions:Although the average high school student listened at safe levels, a small percentage of listeners were exposed to harmful sound levels. Preventive measures are nee- ded to avoid permanent hearing damage in high-risk listeners.

*Corresponding author. Tel.:þ60 3 7967 4918; fax:þ60 3 7967 4775.

E-mail addresses:[email protected],[email protected](K. Seluakumaran).

Available online atwww.sciencedirect.com

Public Health

journa l hom epage: www. elsevier.com /puhe

http://dx.doi.org/10.1016/j.puhe.2013.01.007

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Introduction

The usage of personal listening devices (PLDs) such as mp3 players and mobile phones with a music playback function has become increasingly popular worldwide, with estimated sales of 245 million units in 2012.¹New-generation PLDs have a long battery life, permit storage of a large number of songs, and are capable of producing high sound output levels without distortion. These features allow current PLD users to listen for longer durations and at higher volumes. The high-risk users are teenagers and young adults; prolonged exposure to loud music in these listeners could potentially damage their hearing.²

The maximum sound output level from PLDs can reach 100e120 decibels in A-weighted scale (dBA)^3e6which is equivalent to sound levels produced by a jackhammer or a chain saw.

At high volumes, sound exposure from PLD use could easily exceed the safety limit set for occupational noise exposure levels for acquiring noise-induced hearing loss (NIHL), even if only used for a short duration.^4,6Compared with non-users, PLD users have reportedly shown evidence of subtle cochlear outer hair cell damage^3,7,8 and poorer high frequency hearing thresholds.^9e11It is estimated that up to 5e10% of PLD users may eventually develop some form of permanent hearing impairment after years of PLD use.²Considering the fact that hundreds of millions of PLDs are sold worldwide, even if a small percentage of users were to listen at unsafe levels, this would potentially put millions at risk of NIHL and pose a significant public health issue.^12,13

The popularity of PLD usage globally has also found its way to Malaysia. Due to their affordability and appeal, PLDs have become a must-have gadget for Malaysian teenagers. This study investigated listening habits associated with the use of PLDs in a group of urban high school students in Klang Valley, Malaysia and evaluated the impact on their hearing.³⁰

Methods

Subjects

Subjects aged 13e16 years were recruited from three schools selected at random from a list of high schools located within 20 km of the authors’ university. The appropriate sample size was calculated based on Krejcie and Morgan’s sample size determination table.¹⁴Study participants responded to flyers distributed in classrooms. They had to be regular users of a PLD coupled with either a headphone or earphone for the previous six months. Participation was voluntary and students were allowed to withdraw from the study at any time.

Participants were initially subjected to a face-to-face interview to elicit demographic data and details on PLD usage (type of device used, duration of usage and average listening time per day). Subjects were also asked if they had experienced tinnitus, difficulty in hearing others or ear pain immediately after PLD usage. Those with exposure to other sources of loud noises (e.g. discotheque, concert, school band, noisy tools, home stereo) at least twice per month and prior ear problems were excluded from the study.

Estimation of listening levels

Subjects’ listening levels were estimated using two different methods: self-reported volumes and measured volumes. For self-reported volumes, subjects were asked to mark their usual listening volume on a 5.5-cm horizontal line that cor- responded to 0e100% of the volume setting on their device, and the values were reported as percentage from maximum volume setting. Measured volumes were obtained by asking subjects to set the volume of an Apple iPod Nano(Apple Inc., Cupertino, CA, USA; fourth generation) while listening to the first 40 s of a preselected song (‘Just like Heaven’ by The Cure, mp3 format, 128 kbps bit rate), and measuring the actual output level of the song in decibels. This song was chosen because it was popular and the initial 40 s non-vocal compo- nent has a steady beat with minimal amplitude fluctuation (the silent lead-in period was edited out). During the test, subjects were blinded from the iPod volume setting and told to set it to their usual listening level without considering pref- erence to the test song. The iPod Nano was coupled with an insert earphone (Sony MDR-EX51LP, Tokyo, Japan) and the test was conducted in a quiet environment with 40e50 dBA ambient noise level. The selected music level from the test earphone was measured for 40 s using an artificial ear (KEMAR ear-and-cheek simulator, G.R.A.S. Sound and Vibration, 43AG, Holte, Denmark) connected to a type 1 integrating sound level meter (Norsonic, nor140, Tranby, Norway).

Calculation of hearing risk

To determine hearing risk, subjects’ measured listening levels were compared with internationally recommended occupational noise exposure safety limits for prevention of NIHL.^15,16 These recommendations are expressed as time-weighted av- erages in A-weighted sound levels (dBA), calculated based on continuous exposure to free-field noise for 8 h/day. For com- parison with occupational standards, 1/3 octave frequency band sound levels (0.025e10 kHz) measured from the artificial ear were transformed to equivalent A-weighted free field levels (Lr) as described in an earlier study.¹⁷Following the method used by others,^3,18,19the 8-h equivalent continuous sound level (LAeq8h) was calculated using the following formula:

LAeq8h¼Lrþ10 Log₁₀ðTr=8Þ

whereLris the free-field corrected measured listening level (dBA), andTris the average daily listening duration (h/day).

Measurement of hearing thresholds

All subjects underwent autoscopic examination and tym- panometry (Amplivox, Otowave 102, Oxford, UK) to establish normal external and middle ear functions. Pure-tone audiometry was performed using a precalibrated high-frequency diagnostic audiometer (Siemens hearing instruments, SD28HF, Crawley, West Sussex, UK). Hearing thresholds were established at standard frequencies (0.5, 1.0, 2.0, 3.0, 4.0, 6.0 and 8.0 kHz) and extended high frequencies (9.0, 10.0, 11.2, 12.5, 14.0 and 16.0 kHz) for both ears using the

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modified HughsoneWestlake procedure and expressed in decibels hearing level (dB HL). Following criteria used by others,^10,20subjects’ audiograms were analysed descriptively for incidence of hearing loss [25 dB HL at one or more of the standard frequencies (0.5e8.0 kHz) in either ear] and for evidence of high-frequency notches (10 dB threshold elevation at 3e6 kHz compared with the adjacent frequencies). Hearing tests were conducted using a portable audiometric test booth placed inside a quiet room in the schools, and sound levels inside the booth conformed to permissible levels for audiometric testing specified by the Department of Occupational Safety and Health, Malaysia. Subjects were requested to refrain from listening to their PLDs for 24 h prior to the hearing test.

Statistical methods

Data were analysed using Statistical Package for Social Sci- ences Version 17.0 (SPSS Inc., Chicago, IL, USA). Descriptive analysis (mean, range and standard deviation) was used to describe the following variables; subjects’ age, listening duration, self-reported volume setting and measured listening level. Unpaired Student’st-test was used to compare listening levels and listening durations between male and female subjects. Pearson’s correlation test was used to analyse the association between subjects’ self-reported and measured listening levels, listening levels and listening durations, as well as subjects’LAeq8hexposure levels and hearing thresholds at individual test frequencies. Chi-squared test was used to compare the occurrence of hearing-related symptoms for differentLAeq8hexposure levels. The significance level was set atP<0.05.

Results

After excluding eight subjects due to ear abnormalities and prior ear problems, 177 subjects with a mean (standard deviation) age of 15.21.1 years were included in this study. The majority of participants reported using more than one type of PLD. The most commonly used PLDs were mobile phones (51%

of subjects), followed by mp3 players (36%), laptops (17%) and CD players (1%). The average duration of PLD usage for all subjects was 2.491.48 years.

The mean measured listening level and listening duration for all subjects were 72.2 11.1 dBA and 1.2 1.5 h/day, respectively. The self-reported volume settings of the subjects were significantly correlated with their measured listening levels (Pearson correlation,r¼ 0.716,P<0.001). In addition, subjects who listened at higher volumes tend to listen for longer durations (Pearson correlation,r¼0.188,P¼0.012). When the self-reported and measured volume settings were compared between genders, male students were found to listen at louder volumes compared with female students (Table 1). However, the average listening durations of both groups were similar.

The calculatedLAeq8hexposure levels in all subjects were normally distributed with a mean of 61.6 12.9 dBA and a median of 60.5 dBA (Fig. 1). From the total number of subjects, 17.5% (13 males and 18 females) were exposed toLAeq8h

levels of>75 dBA, which carries a risk of NIHL.¹⁵In addition,

4.5% (three males and five females) of subjects were exposed to LAeq8h levels of85 dBA, which is considered high risk, requiring mandatory hearing protection in an occupational setting.^15,16

In total, 20.9% of subjects reported having tinnitus, 21.5%

had difficulty hearing others and 16.4% experienced ear pain immediately after PLD use. In order to examine the relationship between sound exposure from PLDs and these symptoms, subjects were divided into two groups based to their LAeq8hexposure levels (75 and>75 dBA). The occurrence of these symptoms was not increased when LAeq8h exposure levels exceeded 75 dBA (Table 2).

Hearing loss was found in 13 subjects (7.3%), 12 of whom had mild hearing loss (25e40 dB HL). Five of the 12 subjects had bilateral ear involvement. One subject with an LAeq8h

exposure level of 62.7 dBA had moderate hearing loss (40e70 dB HL) at 6 and 8 kHz in his left ear, and at 8 kHz in his right ear. Seven subjects (3.9%) had notched audiograms (all were unilateral cases). Further statistical analysis showed no significant association between subjects’L_Aeq8hexposure levels and the incidence of hearing loss, or the occurrence of notched audiograms.

When subjects’ hearing thresholds for right and left ears were pooled together at each test frequency and compared with individualLAeq8hexposure levels, there were weak but significant correlations between LAeq8h levels and hearing thresholds at 11.2 and 14 kHz (Table 3).

Discussion

With the increasing popularity of PLDs among teenagers, there is growing concern regarding the risk of hearing damage by improper use of these devices. Detailed population studies about the usage of current PLDs among adolescents and their possible impact on hearing, is limited. Prior studies involved small groups of PLD users3,6,19,21,22

and it is difficult to gen- eralize their conclusions for other populations. The present study investigated the usage pattern of PLDs in a group of Malaysian high school students, and evaluated the potential risks of leisure ‘noise’ exposure on their hearing.

Table 1eSummary of data regarding usage of personal listening devices.

Male Female P-value

Subjects,n(%) 62 (35.0) 115 (65.0) Listening time (h/day)

MeanSD 1.21.3 1.21.6 0.772

Range (0.1e6.0) (0.1e10.0)

Self-reported volume setting (% from maximum)

MeanSD 64.322.6 55.317.7 0.004^b

Range (6e100) (13e100)

Measured volume level (dBA)^a

MeanSD 75.210.6 70.611.0 0.008^c

Range (56.1e94.0) (43.0e94.0)

SD, standard deviation.

a A-weighted free-field equivalent sound levels.

b Statistically significant.

c Statistically significant.

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Listening habits and hearing risk

Subjects’ listening habits differed from the listening patterns described in other populations in several ways. The average measured listening volume obtained in the study subjects was approximately 4 dB higher than mean listening levels in a quiet background reported by two recent studies of Canadian high school students (age 10e17 years)²³and a group of teenagers (age 13e17 years) in Colorado, USA,⁶but was approximately 10 dB lower compared with teenagers (age 13e17 years) in Israel.²⁴The variations in listening levels in different populations could be due to a multitude of sociocultural

factors, including the level of knowledge and attitude of users regarding the risk associated with PLD usage.^6,12In addition, the average listening level in the study subjects was higher compared with listening levels in a quiet environment found among older subjects in other studies.^21,22 This finding is consistent with the notion that teenagers tend to listen to their PLDs at louder volumes compared with adults.^6,12,21

The average listening duration of students in this study (1.2 h/day) was also shorter compared with the average 1.5e3.0 h/day reported in other studies involving teenagers and adult listeners.3,5,6,18,19

At all three schools included in the present study, students were not allowed to use PLDs during school hours. Hence, the only time that the students were able to listen to their devices was outside school hours and at weekends, which explains their shorter listening durations compared with other populations.

This study found that male students were listening to their PLDs at volumes approximately 5 dB louder compared with female students. This finding agrees with other studies which showed a similar trend in high school students^12,23and young adults.^5,19,22The louder listening volumes of male subjects has been attributed to their higher risk-taking behaviour.²⁵

Based on the calculatedLAeq8hlevels, approximately 4.5% of the subjects were exposed to potentially damaging sound levels (85 dBA), which appears to be lower than the estimated pro- portion of high-risk PLD users in other studies.^5,17,18,24As the LAeq8hlevels take into account the listening time, the lower duration of listening in the subjects in the present study should reduce the overall percentage of high-risk users. In addition, it is known that listeners tend to increase their listening levels in the presence of background noise.^6,19,22While listening levels in the present study were measured in a quiet background, which Table 2eRelationship between 8-h equivalent

continuous sound level (LAeq8h) exposure levels and self- reported symptoms of hearing loss.

Symptoms LAeq8h(dBA)

75 >75 Tinnitus

Yes 30 (16.9%) 7 (4.0%)

No 116 (65.5%) 24 (13.6%)

c²¼0.064 df¼1 P¼0.800

Difficulty hearing others

Yes 30 (16.9%) 8 (4.6%)

No 116 (65.5%) 23 (13.0%)

c²¼0.419 df¼1 P¼0.517

Ear pain

Yes 24 (13.6%) 5 (2.8%)

No 122 (68.9%) 26 (14.7%)

c²¼0.002 df¼1 P¼0.966

Fig. 1eDistribution of subjects’ 8-h equivalent continuous sound level (LAeq8h) exposure levels (n[177). Data were normally distributed (skewness[0.123, SE skewness[0.183; kurtosis[L0.232, SE kurtosis[0.363). SE, standard error.

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represents a conservative estimate of the subjects’ actual listening levels, other studies that reported a higher percentage of high-risk users measured listening levels in a noisy environment, which corresponds to listening in the worst-case sce- nario. It should be also noted that a single measurement of listening level in a laboratory setting, as used in the present study, may not be reflective of the variation of actual volume settings used in day-to-day listening in various environments.

Hearing assessment

The extent of hearing damage caused by PLD use is still a subject of debate. Several studies have reported that PLD users have significantly higher hearing thresholds compared with non-users at frequencies between 3 and 8 kHz.^9e11 In addition, hearing thresholds of PLD users at 6 kHz in both ears correlated with exposure levels to their devices.³One study reported that hearing thresholds were worse in PLD users compared with non-users at extended high frequencies (10e20 kHz),¹⁰ but the study methods were criticized for biased selection of controls.²⁶However, other studies found no significant differences in hearing thresholds (up to 8 kHz) of PLD users compared with non-users.²⁷Hearing thresholds of PLD users were mainly within the normal range²¹and were not correlated with listening levels and durations.²⁰

The present study did not find any clear signs of NIHL among the subjects, including in those exposed to unsafe sound levels. Although 7.3% of the subjects had25 dB hearing loss at one or more standard test frequencies, this is only slightly higher than the expected incidence of hearing loss based on a similar criterion in this age group.²⁸While 3.9% of subjects had audiogram notches at 3e6 kHz which is considered indicative of NIHL,²⁰these notches were only found uni- laterally. Furthermore, no significant relationship was found when theLAeq8hexposure levels in individual subjects were compared with the presence of hearing-related symptoms, incidence of hearing loss, occurrence of notched audiograms and hearing thresholds at any of the standard test frequencies.

NIHL due to exposure to continuous loud sound levels is typically a cumulative process, gradually worsening over time. It is estimated that hearing loss due to exposure toLAeq8h

>85 dBA will be evident after at least five years of exposure.² As the average listening duration of the subjects was only 2.6 years, it is likely that hearing damage, if any, is still at an early stage in the majority of subjects. Early-stage hearing loss in PLD users can involve subtle cochlear outer hair cell damage^3,7,8which may not be noticed in standard audiometry.

Although subjects’ hearing thresholds at standard frequencies did not correlate with theirLAeq8hexposure levels, positive correlation was found between exposure levels and

thresholds at two of the extended high frequencies. This finding is critical as it has been suggested that the threshold deterioration at extended high frequencies (>8 kHz) is an early indicator of NIHL.¹⁰

Recommendations

While this study indicates that the average high school student listens to their PLD at a safe level, a significant number of subjects listen at levels that carry risk of NIHL. There is a need for a larger population study to further characterize listening patterns of PLD users and identify likely listeners who are at risk. In addition, long-term impact of PLD usage on hearing should be assessed using longitudinal follow-up studies.

As NIHL is a permanent disability, preventive steps should be taken to reduce possible hearing impairment associated with excessive sound exposure from PLDs. PLD manufacturers should always include a cautionary statement regarding the risk of hearing damage related to listening at a high volume in PLD user manuals. It may also be necessary to introduce legal sound limits for PLDs, as is the case in France (maximum output of 100 dBA). Besides including optional volume limiters, it has been suggested that PLD manufacturers should include visual warning indicators for unsafe levels.²⁹Finally, it is important to educate PLD users regarding hearing health and safe listening behaviour.^12,13In line with this, the authors are presently developing an educational outreach programme to promote safe listening habits among high school students in Malaysia.

Author statements

Acknowledgements

The authors wish to thank the students who participated in this study and the relevant school authorities for their cooperation and assistance during the study period.

Ethical approval

This research was approved by the Medical Ethics Committee of University Malaya Medical Centre (Reference No. 714.10), Malaysian Ministry of Education and the State Education Department. Participation was voluntary and signed consent was obtained from subjects and their parents.

Funding

This work was funded by the University Malaya Research Grant (Project No. RG037 09HTM).

Table 3er-Values andP-values of Pearson’s correlation test between subjects’ 8-h equivalent continuous sound level exposure levels and their hearing thresholds at frequencies of 0.5e16 kHz.

0.5 kHz 1 kHz 2 kHz 3 kHz 4 kHz 6 kHz 8 kHz 9 kHz 10 kHz 11.2 kHz 12.5 kHz 14 kHz 16 kHz r 0.015 0.043 0.017 0.005 0.027 0.050 0.055 0.021 0.089 0.115 0.092 0.154 0.100

P 0.780 0.419 0.751 0.920 0.611 0.345 0.302 0.701 0.095 0.031^a 0.083 0.004^b 0.061

a Statistically significant.

b Statistically significant.

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Competing interests None declared.

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