Scientists have successfully restored hearing in animals by using embryonic stem cells in a breakthrough that brings hope to millions of people with hearing problems.

The new study, published in the journal Nature, showed that human embryonic stem cells helped improve hearing in 18 deaf gerbils by about 46 percent in auditory-evoked response thresholds within, on average, just a few weeks.

The same improvement in humans would be a change from being unable to hear traffic to being able to hear a conversation. What's better is that in some cases, the treatment could help restore hearing to near perfect levels.

Researchers from the University of Sheffield in England said that the work is still an early stage but it raises the possibility that in the future the treatment could help deaf people who currently have no treatment options.

"We have the proof of concept that we can use human embryonic stem cells to repair the damaged ear," says lead author Marcelo Rivolta, a stem-cell biologist at the University of Sheffield, said, according to Nature. "More work needs to be done, but now we know it's possible."

The treatment targets the 10 to 15 percent of the deaf population with damage to sensory neurons and cannot be helped with cochlear implants. However, researchers said that cochlear implants combined with stem cell therapy may help restore healing in people with lost sensory hair cells.

Researchers used stem cells from a human embryo, cells that are capable of becoming any other type of cell in the human body from nerve cells to skin cells or muscle to kidney cell, and converted them into cells similar to spiral ganglion neurons, a type of nerve cell that helps in hearing by sending a representation of sound from the cochlea to the brain.

The newly formed nerve cells were then injected into the inner ears of 18 deaf gerbils, and over 10 weeks the rodents' hearing range improved, on average, by 45 percent.

Researchers said they used gerbils in the study because, unlike mice that hear at a higher pitch range, gerbils hear the same range of sounds as people.

Researchers hope to test the treatment on people within a few years, but they stressed that they still have to determine how long the treatment would last, and whether the treatment is safe as well as effective. If the treatment is determined safe and effective, the level of recovery seen could make a huge difference to patients.

"It would mean going from being so deaf that you wouldn't be able to hear a lorry or truck in the street to the point where you would be able to hear a conversation in this room," Marcott said at a press conference.

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