Hearing loss is consistently associated with an elevated dementia risk, but the size of the effect is modest. A hearing aid does not appear to broadly reduce the risk, at least not as demonstrated in randomised research. The precise causal mechanisms remain unclear.
People with hearing loss do indeed have a statistically demonstrable higher risk of dementia than people with normal hearing. Large cohort studies and meta-analyses report hazard ratios of approximately 1.07 to 1.28, representing a modest but consistent elevated risk. An older, smaller study found larger figures (up to a factor of 5 for severe loss), but those findings are not confirmed to that magnitude by more recent, larger studies. (PMID 38175662, 29222544, 21320988)
The more severe the hearing loss, the higher the estimated risk. At the same time, the majority of people with hearing loss do not develop dementia, and the association in all these studies is correlational, not proven causal. Other factors may be involved that affect both hearing and the brain. (PMID 21320988, 38175662)
At the population level, hearing loss in middle age is one of the larger modifiable risk factors: international estimates point to a contribution of around 9% of all dementia cases worldwide. This makes it, in theory, an important target for prevention. Hearing loss is also an independent risk factor for dementia that begins before the age of 65. (PMID 32871106, 38147328)
A frequently asked question is whether a hearing aid can prevent dementia. Observational studies suggest that people with hearing loss who use a hearing aid have a lower dementia risk than those who do not (HR 1.06 versus 1.20 compared with normal hearing). However, in the largest randomised trial to date, the ACHIEVE study with 977 participants, a hearing aid intervention did not reduce cognitive decline over three years in the overall group. Only in older adults who already had more risk factors did there appear to be some benefit. The hearing aid is therefore not a proven means of broadly preventing dementia. (PMID 38175662, 37478886)
Why the association exists has not yet been clarified. Proposed mechanisms include: the brain having to work harder to process sounds (additional cognitive load), a reduction in sensory input from the outside world, or a shared underlying brain disease. Furthermore, hearing loss more often goes hand in hand with social isolation and depression, which themselves also raise the risk of dementia. This makes it difficult to determine what is directly cause and what is effect. (PMID 32871106, 30291149)
The claims are based on multiple large prospective cohort studies (including UK Biobank, n=356,052), a meta-analysis of prospective studies, and one randomised controlled trial (ACHIEVE, n=977). The evidence for the association is strong; the evidence for causality and for the effect of hearing aids is moderate.