Hearing Loss
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In the 1980s, audiologists began cautioning lovers of loud music about hearing loss that could potentially result from use of their Walkman or portable compact disc (CD) players. More than thirty years later, the integration of portable digital devices that play music are more abundant than almost every other electronic device in the world, and all of them have an earphone jack. Scientists from the University of Leicester have shown for the first time how noises louder than 110 decibels (dB) cause cell damage which ultimately leads to hearing loss.

Noise-induced hearing loss affects millions and it can be caused by exposure to loud noise over long periods of time, or by loud, short bursts of sound such as gunshots or fireworks.

Although people seem to be more aware of the impact of noise on their hearing, it's not clear whether they're changing their behavior, says Nancy Nadler, director of the Noise Center of the League for the Hard of Hearing in New York City. "We need to help people understand how important their hearing is to them before it's too late. Because once you suffer from a noise-induced hearing loss, there's very little you can do. You cannot get your hearing back," at least not under normal circumstances Nadler stresses.

The researchers said that earphones or headphones on personal music players can reach noise levels similar to those of jet engines, which can reach 140dB at 100 feet distance.

The previous study published in the International Journal of Audiology, demonstrated that teens have harmful music-listening habits when it comes to iPods and other MP3 devices. "In 10 or 20 years it will be too late to realize that an entire generation of young people is suffering from hearing problems much earlier than expected from natural aging," says Prof. Muchnik of TAU's Department of Communication Disorders.

Environmental Noise
Telephone dial tone 80dB
City Traffic (inside car) 85dB
Subway train at 200 feet 95dB
Hearing Loss at Sustained Levels
Hand Drill 98dB
Lawn Mower at 3 feet 107dB
Pain Begins 125dB
Short-Term Exposure Can Cause
Permanent Damage
Jet engine at 100 feet 140dB
12 Gauge Shotgun Blast 165dB
Death of hearing tissue 180dB

Noises louder than 110 decibels are known to cause hearing problems such as temporary deafness and tinnitus (ringing in the ears), but the University of Leicester study is the first time the underlying cell damage has been observed.

The latest study has been published in the Proceedings of the National Academy of Sciences.

University of Leicester researcher Dr Martine Hamann of the Department of Cell Physiology and Pharmacology, who led the study, said:

"The research allows us to understand the pathway from exposure to loud noises to hearing loss. Dissecting the cellular mechanisms underlying this condition is likely to bring a very significant healthcare benefit to a wide population. The work will help prevention as well as progression into finding appropriate cures for hearing loss."

Nerve cells that carry electrical signals from the ears to the brain have a coating called the myelin sheath, which helps the electrical signals travel along the cell. Exposure to loud noises -- i.e. noise over 110 decibels -- can strip the cells of this coating, disrupting the electrical signals. This means the nerves can no longer efficiently transmit information from the ears to the brain.

However, the coating surrounding the nerve cells can reform, letting the cells function again as normal. This means hearing loss can be temporary, and full hearing can return, the researchers said.

Dr Hamann explained: "We now understand why hearing loss can be reversible in certain cases. We showed that the sheath around the auditory nerve is lost in about half of the cells we looked at, a bit like stripping the electrical cable linking an amplifier to the loudspeaker. The effect is reversible and after three months, hearing has recovered and so has the sheath around the auditory nerve."

The findings are part of ongoing research into the effects of loud noises on a part of the brain called the dorsal cochlear nucleus, the relay that carries signals from nerve cells in the ear to the parts of the brain that decode and make sense of sounds. The team has already shown that damage to cells in this area can cause tinnitus -- the sensation of 'phantom sounds' such as buzzing or ringing.

EU Consumer Affairs Commissioner Meglena Kuneva, said, "I am concerned that so many young people, in particular, who are frequent users of personal music players and mobile phones at high acoustic levels, may be unknowingly damaging their hearing irrevocably."

Hearing loss caused by continuous exposure to loud noise is a slow and progressive process. People may not notice the harm they are causing until years of accumulated damage begin to take hold, warns Prof. Muchnik. Those who are misusing MP3 players today might find that their hearing begins to deteriorate as early as their 30's and 40's -- much earlier than past generations.

Marco Torres is a research specialist, writer and consumer advocate for healthy lifestyles. He holds degrees in Public Health and Environmental Science and is a professional speaker on topics such as disease prevention, environmental toxins and health policy.