Hearing loss 'may be an early warning sign of dementia'

People who are hard of hearing have increased odds of developing dementia as they age, according to a U.S. study.

Scientists found those with mild hearing loss had nearly twice the chance of developing dementia compared to people with normal hearing, even after ruling out the influence of age and other factors.

The risk increased three-fold for those with moderate hearing loss, and five-fold for severe impairment.

Hearing aid

Using a hearing aid could stop older people feeling isolated, which may cause an increased risk of dementia

However, scientists are not sure whether hearing loss and a decline in mental function go hand in hand, or whether deafness isolates a person, which in turn  increases their risk of dementia.

The study led by Johns Hopkins University surgeon Frank Lin, followed more than 600 men and women aged 36 to 90 over an average of 12 years.

All had a hearing test done at the start of the study, but none had dementia at that point.

Overall, nine per cent of the participants developed some kind of dementia during the study, which was published in the Archives of Neurology, most commonly Alzheimer's disease.

Colleagues showed that the worse the participants' hearing, the greater their dementia risk.

Dr Lin said: 'Does it mean you will develop dementia if your hearing is impaired? Absolutely not. But is your risk increased? You betcha.'

He noted that the reasons for the link are unclear, saying there were three possibilities, such as hearing loss and dementia sharing a common, unknown cause.

A different possibility is that elderly people who are hard of hearing may have extra difficulties coping with declining mental function, or that the social isolation and loneliness caused by declining hearing could also fuel the dementia.

Should these last two be the case, Dr Lin added, there could be a significant impact on public health and healthcare spending.

According to the U.S. National Institutes of Health, 17 per cent of U.S. adults have some degree of hearing loss.

'Treating hearing loss is not going to hurt you, except perhaps your wallet,' Dr Lin said, noting that he is currently running a trial to see if treating hearing loss would delay the onset of dementia.

'We really need to begin studying what the exact mechanism is. And we need to begin studying whether hearing aids could have an effect on the onset of dementia.'