Hearing Loss
© Robert Essel NYC / Getty Images
It seems your parents were right. Too much loud music isn't good for you.

US scientists say they have shown that age-related hearing loss - presbycusis - is mainly caused by damage to hair cells, the sensory cells in the inner ear that transform sound-induced vibrations into the electrical signals that are relayed to the brain by the auditory nerve.

This challenges the prevailing view of the past 60 years that age-related hearing loss is mainly driven by damage to the stria vascularis, the cellular "battery" that powers the hair cell's mechanical-to-electrical signal conversion.

In other words, hearing loss is not so much a natural consequence of getting old, as the result of decisions made when young. In humans at least.

"It's likely that if we were more careful about protecting our ears during prolonged noisy activities, or completely avoiding them, we could all hear better into old age," says Charles Liberman from Massachusetts Eye and Ear, co-author of a paper in the Journal of Neuroscience.

The inner ear cannot be biopsied so the research team, led by Pei-zhe Wu, examined 120 specimens collected at autopsy, using multi-variable statistical regression to compare data on the survival of hair cells, nerve fibres, and the stria vascularis with the patients' audiograms to uncover the main predictor of the hearing loss.

They found that the degree and location of hair cell death predicted the severity and pattern of the hearing loss, while stria vascularis damage did not.

The researchers say the findings are good news given recent progress in the development of therapies to regenerate missing hair cells. No one is focusing on approaches to regenerate the stria vascularis.

And why have so many previous studies produced different results? Likely because they have used animals, which don't experience the same auditory abuses (aka loud music) as humans.

In ageing laboratory animals, there is very little loss of hair cells, compared to humans, even at the end of life, the researchers say. However, there is prominent damage to the stria vascularis.