The Impact Of Biovariability In Hearing Loss

Like many people, you’ve probably found yourself in a situation or two where the noise level is high and your ears are completely unprotected. You may have fretted over the thought that your hearing may be exposed to damage, or you may have been very young and not had that thought at all.
Previous Understanding
General knowledge about the effects of noise exposure has been well established for some time now. We know that each time we’re exposed to noise levels above 85 dB, the tiny sound receptive hairs of our cochlea become damaged. A few hairs here or there won’t result in a big consequence in the long term, unless the exposure to high level of noise is consistent, or occurs often over time. Once enough microscopic hairs experience damage (that, by the way, is irreversible) hearing loss ensues.
Up until recently the assumption that everyone exposed to the number of unhealthy noise levels carries the same risk of hearing loss. Person A who is exposed to 120 dB of noise twice a week for six months is just as likely to experience damage as Person B exposed to the same circumstances. General advice has been given across the board, that if you know you’re going to be in environments with unhealthy noise levels, protect yourselves by bringing earplugs or minimizing your exposure.
Changing Understanding
A new study may be changing our outlooks on noise exposure, however. /a team at the Naval Postgraduate School in Monterey, California lead by Dr. Hong Zhou hypothesized that physiological differences within people or one person at different ages can create variations to the response from noise exposure.
To test this hypothesis, Dr. Zhou’s team studied the effects of noise exposure on a group of chinchillas. They placed shock tubes in different proximities to each chinchilla that ranged in intensity. The result confirmed their hypothesis. Chinchilla overall hearing loss was lower compared to their predictions based off of the assumption that all chinchillas would be exposed to the same level of damage.
Range Of Susceptibility
They saw that there was actually a range of reactions to the stimuli. Some chinchillas were less susceptible to hearing loss than what was predicted, while some other chinchillas were more susceptible to hearing loss. These results have implications for the way we view susceptibility to hearing loss in humans.
However, hearing loss across the board is still a possibility when repeated exposure to loud environments occurs. The next step in this research will be to isolate what specific genetic factors determine when an individual is more susceptible to hearing loss than other people.
This group of the population will need to take extra care in their hearing health, and not assume that a little exposure to noisy environments is tolerable on occasion.
Individual Variation
This new discovery could help us understand why we are more susceptible to hearing loss as we age, also. The general understanding was that as we age, all of the noisy circumstances we’ve exposed ourselves too in the past have had a cumulative effect, and the consequences may be catching up to us. Knowing that we may be more or less susceptible to hearing loss at different times in our life may offer a good deal of explanation why our hearing is so susceptible in old age.


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