Hearing loss in older people is associated with decline in cognitive ability and dementia, according to new research by scientists at Trinity College Dublin.

The research involved a review of 36 previous studies from 12 countries involving 20,264 participants.

Previous studies had found opposing answers to the question of whether or not hearing loss and cognitive decline are connected.

As a result, researchers at Trinity's Institute of Neuroscience and Global Brain Health Institute decided to review the existing literature to see if they could bring clarity to the situation.

Their meta-analysis only included observational studies that used standard cognitive tests and pure-tone audiometry, which is the clinical standard for assessment of peripheral hearing loss.

They concluded that cognitive decline including processing speed, episodic memory and executive function was higher in those whose hearing had declined as they grew older, and they also had a higher risk for cognitive impairment and dementia.

More research will be required to establish whether or not the link between the two issues is causal.

"We need intervention trials that look at the benefits of hearing loss treatment over a long follow-up period to see if it decreases the risk of someone getting dementia," said David Loughrey, PhD student and Global Brain Health Institute Fellow at TCD.

Possible connections could include the diversion of mental resources to make up for the loss of hearing leaving fewer resources for other processes such as memory.

But research also suggests that other conditions such as depression or loneliness could be connected to a higher risk of dementia.

The research was published in JAMA Otolaryngology - Head & Neck Surgery.