After Joe Poolman started becoming confused and was diagnosed with severe hearing loss, his family wondered if the two conditions may be related.

From South Africa and now living in the Auckland suburb of Pakuranga, the 87-year-old had been involved in rugby, but stopped watching it on TV because he could no longer hear the commentary.

"He was more grumpy, depressed and hard to communicate with," said daughter Ronel Schodt, the communications officer of the National Foundation for the Deaf.

"Dad started to withdraw from community activities and even more so from us."

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"[He] keeps forgetting things and he even asked the doctor if this was an early sign of Alzheimer's or dementia. The answer given by the doctor was that it was part of the ageing process, which was not very reassuring."

Schodt had been reading about the associations researchers have found between hearing loss, and cognitive decline and dementia.

A world leader in this field, Associate Professor Frank Lin, of Harvard University in the United States, will soon visit New Zealand to give lectures.

Schodt said, "The question is whether the emerging effect of hearing loss on cognitive decline can be stopped with early intervention with hearing amplification, for example when the first signs of communication problems caused by hearing loss are visible."

It is estimated that around 880,000 Kiwis suffer hearing loss, but fewer than 20 per cent are using hearing aids.

New Zealand hearing loss prevalence rates by age and gender. Source/Listen Hear! NZ report, National Foundation for the Deaf
New Zealand hearing loss prevalence rates by age and gender. Source/Listen Hear! NZ report, National Foundation for the Deaf

Poolman will have further tests of his memory and thinking abilities next month, and he is seeking referral to an ear, nose and throat surgeon for further investigation of his hearing.

Next week, he will receive his first hearing aids and Schodt hopes they will make a big difference.

Lin told the Herald that although the research linking hearing loss to declining brain function was observational and could not show cause and effect, it was strong evidence.

"The magnitude is quite large so I think that addressing hearing loss can make a difference."

One study found that older adults with hearing loss developed a significant impairment in their cognitive abilities more than three years earlier than those with normal hearing.

On dementia, his group found that the worse an elderly person's hearing loss, the greater the risk of developing dementia. A person with severe hearing loss had five times the risk of a person with normal hearing person of developing dementia. The link remained strong, even after taking into account other factors associated with risk of dementia, including diabetes, high blood pressure, age, sex and race.

A later study, using MRI scans, found that brain shrinkage seemed to occur faster in the hearing-impaired than in other elderly people.

Lin said possible explanations for the cognitive decline associated with hearing loss included the links between hearing loss and social isolation, because loneliness is known to be a risk for cognitive decline.

Also, impaired hearing might force the brain to expend too much energy on processing sound, at the expense of memory and thinking. And there could be some underlying damage that leads to both hearing loss and cognitive problems.

To answer the question of cause and effect, Lin and colleagues are planning a clinical trial. Among some 850 elderly people with hearing loss, the rate of cognitive decline will be compared between those given optimum hearing treatment and those given standard healthy ageing interventions covering nutrition and exercise.

• Visit the Pindrop Foundation for details of Frank Lin's address to the Cochlear Implant Forum on March 11.