A US study found that elderly patients with hearing loss experienced 30-40% greater cognitive decline over six years, bringing forward the onset of significant impairment by over three years.
Authors suggested social isolation may be behind the link.
The Alzheimer's Society said it was unclear whether hearing loss causes cognitive decline or just shares risk factors with dementia.
Earlier studies had linked hearing problems to dementia and suggested it may be due to changes in the brain or reduced social engagement. But results have been mixed.
The new findings, published in the journal JAMA Internal Medicine, came from a study of 1,984 elderly adults in the US.
Patients without cognitive problems at the start of the study had their hearing and mental function assessed. This was repeated after six years.
Researchers found that after this time, patients with hearing loss >25 dB had 32-41% lower cognitive function scores than those with normal hearing. Rates of decline were directly linked to hearing loss at the start of the study.
Authors concluded: 'Our results demonstrate that hearing loss is independently associated with accelerated cognitive decline and incident cognitive impairment in community-dwelling older adults.'
Jess Smith, research officer at the Alzheimer’s Society, said: 'As risk of hearing loss increases with age, it is in some ways not surprising to hear that it could be linked to dementia. However, this research doesn’t answer the question of whether this is a cause of cognitive decline or one of a number of conditions that share risk factors with dementia.'