- New research says hair cell loss is more significant to age-related hearing loss than strial atrophy
- This loss is caused by noise abuse in industrialised societies
- Animals' age-related hearing loss has a completely different pattern, adding to the evidence
Hearing is a vital part of human social life – and losing this important sense in our old age can contribute to loneliness and cognitive decline.
Around 50% of 85-year-olds suffer from hearing loss – and new research says it's our own fault.
How hearing works
But first, it's important to understand how our ears work: Little hair cells in our inner ear convert sounds into electrical signals that are sent to the brain for processing.
The stria vascularis – a part of the inner ear associated with low frequencies – acts as a battery and drives an electric current into the hair cells when activated by sound.
Previously, the main conclusion was that age-related hearing loss was a result of that battery slowly losing its juice due to cell degeneration (strial atrophy). When it came to high-frequency hearing loss, the cause was generally regarded as noise that humans in urban environments are exposed to.
But new research published in JNeurosci instead proposes that, in fact, hair cell loss plays a much bigger role. Instead, it's our abuse of our ears that's causing age-related hearing loss, with strial atrophy having almost no impact.
The main way that we test hearing is through an audiogram, the measurement of the audible threshold where participants are asked to signal whether or not they hear a certain frequency. Humans can hear between -10 decibels and 15 decibels. However, one cannot see the physical damage in the inner ear while a patient is still alive, thus researchers have to rely on autopsies to see the real damage.
The researchers studied 120 preserved ears from the Massachusetts Eye and Ear collection from deceased people that underwent "normal ageing" between the ages of one and 104 years.
While they found that strial atrophy was common in ageing ears, they didn't find it had a significant correlation with hair cells' survival.
Noise pollution the biggest cause
On the other hand, they found that long-term noise exposure – like working in loud factories – increased hair cell loss and might have a far bigger impact on hearing loss as we age.
They also compared age-related hearing loss biological patterns in humans to animals, that don't present with the same damage as humans, with more strial atrophy than hair cell loss. The researchers conclude that this is due to animals not living in industrialised environments.
However, there's still a lot scientists don't know about strial atrophy.
"The prevalence of strial atrophy presents a challenge for therapeutics designed to restore hearing: regenerating hair cells will not restore normal thresholds to ears with strial atrophy, and present results suggest no clear-cut way to diagnose the degree of strial damage," write the researchers.
Importance of study
This study is important because new treatments for hearing loss are being trialled that target hair cell loss, and understanding the reasons why hearing loss is centred on the inner ear structure is needed to provide better care.
"If true, the bad news is that we are all abusing our ears, to our significant functional detriment, as we age," add the researchers.
"The good news is that raised consciousness about the dangers of noisy environments could lead to an improved hearing prognosis for the ageing population."