Wednesday June 23 2010
The study cannot tell us about long-term hearing changes
“Just one hour listening to an MP3 player can damage hearing,” reports the Daily Mail. The newspaper says that the temporary changes seen after listening to a MP3 player “may lead to long-term harm”.
These findings come from a small study looking at hearing in 49 young adults aged 19 to 28. It found that one hour of listening to pop-rock music at above 50% volume resulted in temporary changes in hearing sensitivity. However, hearing reverted to normal within 48-hours.
This study suggests that an hour of listening to a MP3 player can temporarily affect hearing, although it does not tell us what the longer term effects of frequent exposure would be. However, it is already known that frequent exposure to loud noise can affect hearing, so it seems sensible to not listen to personal music players at loud volume for extended periods of time.
Where did the story come from?
The study was carried out by researchers from Ghent University in Belgium, and partly funded by a scholarship from the Research Foundation in Flanders, Belgium. The study was published in the peer-reviewed medical journal Archives of Otolaryngology Head and Neck Surgery.
Both the Daily Mail and The Daily Telegraph have covered this story accurately.
What kind of research was this?
This was a non-randomised comparative study looking at how listening to a commercially available MP3 player for one hour affected hearing. The study also looked at how loud the output of a commercially available MP3 player was.
Ideally, studies of this type should randomly assign their participants into groups whenever possible. This is the best way of ensuring that the groups are balanced for known and unknown factors that can affect results. The lack of randomisation in this study is a limitation.
What did the research involve?
The researchers enrolled 21 young adult volunteers to listen to music on an MP3 player, and 28 young adult volunteers for the control group. The volunteers in the MP3 group had their hearing tested before and after listening to one hour of pop-rock music on the MP3 player. The test was repeated using two different types of headphones and at different volume levels.
Volunteers were aged 19 to 28 years. They had to have no recent history of ear disease, and had normal hearing on hearing tests. The MP3 player used in the experiment was a second-generation iPod Nano. Before testing on the volunteers, the sound pressure levels of one hour of pop-rock music on the iPod were assessed using a head and torso simulator. Pressure levels were assessed for volume settings between half and full volume (as measured on the volume bar) when using both standard in-ear headphones and for “supra aural” clip-on headphones that hook over the top of the ear.
The music volunteers listened to a maximum of six one-hour sessions, with at least 48 hours between each session. Four sessions were carried out with volumes at either 50% or 75% of the maximum with the two different headphones. The final two sessions were at more than 75% volume, at a level that the individual found loud but comfortable, again using the two different headphones. Six participants did not take part in these final sessions as they found the music too loud.
Hearing was assessed using various tests before and after listening to the music, or after one hour of not listening to music in the control group. These included a test of the threshold at which volunteers could hear, and the ability of the inner ear to respond to short bursts of sound or two simultaneous tones of different frequencies.
The researchers compared hearing before and after each music session, and looked at whether responses differed between those listening to music and the controls.
What were the basic results?
The researchers found that at half to full volume on the iPod Nano, loudness ranged from 76.87 to 102.56 decibels (dBA) for the standard in-ear headphones (earbuds) and from 71.69 to 97.36dBA for the “supra-aural” headphones. The standard in-ear headphones were on average 5.55 dBA louder than the supra-aural headphones at these volume levels.
The music group showed changes in their hearing thresholds and the cochlea’s response to short bursts of sound after listening to the MP3 player for an hour. There were no changes in the cochlea’s response to two simultaneous tones of different frequencies. These changes occurred more frequently in the music group than in the control group.
Hearing did not differ between the pre-music tests given at each session. This suggests that the changes in hearing associated with the music were temporary and they returned to normal within 48 hours.
How did the researchers interpret the results?
The researchers concluded that the temporary changes in hearing sensitivity observed “indicate the potential harmful effects of listening to an MP3 player”. They say that further research is needed to assess the long-term risk of cumulative noise exposure on the hearing of adolescents and adults.
This small non-randomised study suggests that listening to music on a MP3 player for an hour results in some temporary changes to hearing sensitivity. However, there are some limitations:
- The study was small and only included young adults with normal hearing. The results may not be representative of all young adults or of people in different age groups.
- As the control group and music group were not randomly assigned, there could be differences between these groups (other than the music) that could be influencing results.
- The study only looked at the hearing changes immediately after an hour of listening to music on the MP3 player. It cannot tell us about the longer-term effects on hearing.
Frequent exposure to loud noise is already known to affect hearing, so it seems sensible to not listen to personal music players at loud volumes for extended periods of time.