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The iPod and hearing loss in youth

Up to 10% are at high risk for permanent hearing loss

From across the subway car, you hear the strains of a current teen anthem leaking from the ear buds of an iPod plugged into a teenager, apparently also reading her history textbook. You can almost make out the lyrics. Can this be good for her hearing? Does that noise interfere with her ability to learn? 

According to a recent large scale report from scientists of the European Commission examining the use of personal music players (PMP) such as the iPod, the answer to the first question is no: as many as 1 in 10 users of personal music players is at risk to suffer permanent hearing loss if they listen to a PMP at high levels more than one hour a day for five years. And to the second question, yes: her learning efficiency is likely compromised by the noise.

To prepare this report, a Working Group from the Scientific Committee on Emerging and Newly Identified Health Risks (SCENIHR) of the Direcorate-General for Health & Consumers of the European Commission, considered evidence from a range of sources. These included peer-reviewed scientific studies, and published reports of professional, government, and non-governmental organizations. The Working Group also considered all replies to a Call for Information issued by the Commission.

From this wealth of data, the group performed a health risk assessment, determining whether a hazard exists, the magnitude of the effect, and the risk associated with different patterns of exposure. They assessed exposure in the general population, and estimated the impact of exposure on total burden of disease. 

Measuring sound exposure

Sound exposure is assessed as sound pressure level, measured as a logarithmic scale with the decibel (dB) as a unit.

Source or observing situation Typical sound pressure level (dB)

Hearing threshold

Leaves fluttering

Whispers in the ear

Conversational speech

Cars for a close observer

Airplane taking off (close observer)

Pain threshold

0 dB

20 dB

30 dB

60 dB

60 to 100 dB

120 dB

120 to 140 dB

 

Long-term exposure to sounds above 85 dB is the critical level for hearing loss.   The European Commission requires that ear protection be provided for daylong exposure to 80 dB sound in the workplace. But there is a time-intensity trade-off. For example, two minutes of exposure to a sound of 104 dB in a nightclub is equivalent to eight hours of exposure to sound at an 80 dB level. Listening to a personal music player at 95 dB, measured at the ear, for 15 minutes a day would equate to eight hours of exposure to an 80 dB level. 

How does noise-induced hearing loss happen?

Noise-induced hearing loss (NIHL) takes place gradually and is often unnoticed until it reaches a certain level. It results from damage to the outer hair cells of the cochlea. The outer hair cells amplify low-level sounds that enter the cochlea. Damage to the inner hair cells that actually convert the sound waves to electrical signals and transmit them to the brain is very rare. Damage to the outer hair cells and the associated hearing loss is irreversible. Current estimates indicate noise-induced hearing loss affects from 10 to 15 million people in United States. The figures below show the location of the cochlea and the outer hair cells of the ear. 

 

Inner Ear Anatomy
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The inner ear is buried in the bone of the skull. It contains the organ of balance (vestibular system) and the organ of hearing (cochlear system).

 

Hearing: Organ of Corti
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The receptor organ for hearing - the organ of Corti - is located in the cochlear duct of the cochlea. The outer hair cells act as amplifiers of sound. They are the cells more commonly damaged by loud noises.

 

See " Introduction to the Ear" for an interactive guide to the anatomy of the ear.

It's not just noise that can cause hearing problems

Other factors can mediate noise-induced hearing loss. The vulnerability of outer hair cells depends on a number of factors such as genetics, gender, age, and hypertension. Therefore, there is much variability among individuals in risk of hearing loss. Smoking is a risk factor for potentiating noise-induced hearing loss. Some drugs, such as cis-platinum used in cancer chemotherapy, can cause hearing damage. Other classes of drugs have also been implicated in damage to hearing, for example some antibiotics. Although some drugs have been shown experimentally to be protective against noise-induced hearing loss, the main treatment is prevention. The video clip, courtesy of redorbit.com, illustrates the mechanism of hearing loss and shows the results of a study of the risk associated with listening to PMPs.

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The iPod and other Personal Music Players

The volume PMPs produce varies from manufacturer to manufacturer, and the type of earphone used influences the sound level that reaches the ear canal. Ear-bud type headphones produce the highest levels in the ear canal. The quality of current digital music formats and the technology of PMPs allow music to be played at very high levels without distortion. Levels of 85 db to 115 db are possible across a range of devices, with maximum levels reaching 121 dB in some situations. 

As Dr. Blake Papsin, Otolaryngologist and Director of the Cochlear Implant Program at The Hospital for Sick Children observed, "Earbuds are dangerous by design.  They are designed to deliver high levels of sound in the ear canal in noisy environments." 

Listening habits: who is at risk?

One study showed that when youth adjust a PMP for enjoyment in a quiet room, the average level was 85 dB but preferred levels were higher in noisy environments. Other studies show that in various environments, listening levels range between 70 dB and 90 dB, but up to 40% of individuals in noisy environments, for example commuting to work, exceed a listening level of 80 dB. Across a number of studies, average weekly exposure to personal music players ranges from one to 14 hours, with men listening for longer than women. Given an average eight-hour equivalent listening level of 75 to 85 dB, 5% to 10% of these young listeners are at high risk of developing permanent hearing loss after five years of exposure.

Stated simply, as many as 1 in 10 users of PMPs are at risk to suffer permanent hearing loss if they listen to a PMP at high levels more than one hour a day for five years.

Dr. Papsin points out that across human generations, cumulative noise related hearing loss becomes greater.  "Our grandparents had less hearing loss than our parents, and we have more hearing loss than our parents - we live in noisier environments and exposure ourselves to more loud music and noise sources like motorcycles and snow mobiles."  So total noise exposure in an urban environment, including social events attended by youth such as rock concerts nightclubs and discotheques add to the risk of hearing loss by age 50.

Other possible effects of exposure to PMPs

Although few studies have addressed the effects of listening to PMPs on cognitive and physiological processes, a number of studies have looked effects of excessive noise on cardiovascular function, cognition, and distraction. Both acute and cumulative effects have been shown. For example, relatively short exposure times (15 minutes) to moderate levels of ambient noise (55-65 dB) have been shown to impair learning. However, the authors conclude that although it reasonable to assume that listening to music with a PMP could hamper memory and learning when reading from a text, there is insufficient evidence to show that voluntary PMP-listening leads to lasting and permanent impairments in cognition and attention. 

Prevention strategies

A study published in the journal Pediatrics reported the results from a sophisticated web-based survey that looked at ways to prevent mp3-related hearing losses in teenagers. Participants included experts in fields such as scientific research, medical practice, community health, education, youth work, music entertainment, and enforcement.

The study involved three rounds of surveys, the first to evaluate prevention strategies to prevent hearing loss and the second two to allow the participants to reach a consensus concerning which of the strategies were feasible and would have the most impact.

Teenagers, and indirectly their parents, bear the responsibility for the safe use of personal music players such as iPods. However, the experts who participated in this study did not believe that teenagers as a group would follow practices recommended to prevent hearing loss. Consensus was reached on two proposals:

Regulatory authorities such as government should create guidelines for manufacturers of personal music players that would result in products that are safe to operate.

Public health campaigns that increase understanding of the risks of listening to loud music and suggest preventative measures that may be adopted were also thought to be an effective and feasible strategy.  Though it may be an uphill battle: "Our culture does not encourage responsible use of iPods," says Dr. Papsin.   Listening to loud music and the use of iPods is encouraged by the examples of celebrities, television shows targeting youth, and movies. 

Given that the Hearing Alliance of America has recently reported that 15% of college graduates have hearing loss that is equal to or greater than their parents', mainly as a result of listening to loud music, immediate action from regulatory authorities and departments of public health is required to prevent significant hearing loss across a generation of youth.

How to listen to your portable music player responsibly

  • Do not listen to your music at high levels.
  • If your player has a feature that allows you to set maximum listening level, set it to three quarters of maximum volume.
  • If your player does not come with this feature, check the manufacturer's website to see if there is a software or firmware upgrade that would add this feature.
  • Limit the amount of time your listen to your PMP each day.
  • If you listen to your player in noisy areas, consider using noise isolation or active noise cancelling headphones. With these, you do not need to turn the music up to hear it above the noise that is around you. Some models of ear buds also take advantage of these or similar technologies.

Isolation from the environment poses the real health risk of PMPs

Sound helps you know what is happening around you. Listening to a PMP can shut out the sound of fire alarms and other warning signals as well as the sound of approaching vehicles, cyclists, or pedestrians you have not seen.  Although Dr. Papsin believes PMP usage will contribute to hearing loss in the longer term, his main concern with PMPs is not hearing loss.  "The real health risk of iPods is immediate: physical trauma from falls or incidents such as pedestrian-motor vehicle crashes that arise as a result of the distraction and environmental isolation that comes from listening to a PMP." 

Ross Hetherington, PhD, C.Psych
Managing Director and Editor-in-Chief,
AboutKidsHealth

For more information: www.apple.com/sound

 

The Apple website has information on sound and hearing, and links to downloads of firmware upgrades to add a volume-limiting feature to older iPods.

www.canadianaudiology.ca

The Canadian Academy of Audiology has information about hearing, hearing loss, and treatment in children and adults.

6/17/2010

Vogel I, Brug J, van der Plueg CPB, Raat H. Strategies for prevention of mp3 hearing loss among adolescents: Expert opinions from a Delphi study. Pediatrics. 2009;123:1257-1262. Available from: http://pediatrics.aappublications.org/cgi/content/full/1212573/5/1257 [accessed 2009 May 19].

Scientific Committee on Emerging and Newly Identified Health Risks (2008). Potential health risks of exposure from personal music players and mobile phones including a music playing function. Directorate-General for Health & Consumers, European Commission. Downloaded from http://ec.europa.eu/health/ph_risk/committees/04_scenihr/docs/scenihr_o_018.pdf October 20, 2008.





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