Can Hearing Aids Help Prevent Dementia?

If you go on the websites of leading hearing aid brands you’ll see marketing claims implying their products can prevent or forestall cognitive decline, for example, referring to the “proven link between untreated hearing loss and the development of Alzheimer Disease and dementia.” It’s true that people with hearing loss tend to be more likely to be cognitively impaired, a correlation that’s been observed since at least the 1960s. The risk of incident dementia is up to nearly fivefold higher in those with severe hearing loss. But that association could arise in at least one of two ways.

The “common factors hypothesis” posits that hearing and cognitive disorders only appear linked because they share a common cause, neurodegenerative processes due to things like clogged arteries or oxidative stress. On the other hand, the “peripheral-central impairment hypothesis” suggests that hearing difficulties lead to thinking difficulties because the brain is forced to recruit extra processing power to decipher the garbled sound, which comes at a more general cognitive cost. If that were the case then hearing aids really could have the potential of helping the brain. There’s only one way to find out: test it.

There has been a lack of randomized controlled trials. Observational studies showed slower rates of memory decline after people started using hearing aids compared to before, but that still doesn’t prove cause and effect. There was a trial in which about 200 elderly veterans with hearing loss were randomized to hearing aids or to join a waiting list to get them later. Those who got them had significant improvements in quality of life, mood, and cognition compared to the control group. But waiting list groups tend to be weak controls since you’re randomizing people to do something versus nothing and therefore can’t discount the placebo effect.

The Aging and Cognitive Health Evaluation in Elders study ran a pilot trial in which men and women aged 79 to 84 with hearing loss were randomized to hearing aids or a quote-unquote “successful aging” health education program. No effect on cognitive decline was found. Even if there had been, though, one might imagine that the positive expectations inspired by discernible changes in hearing might lead to more substantial placebo effects. Ideally, we’d have a placebo-controlled trial: real hearing aids versus sham hearing aids.

Researchers in France published the first multicenter double-blind randomized placebo-controlled trial that randomized hearing-impaired Alzheimer’s patients either to regular hearing aids or to tampered hearing aids that mimicked the real thing but only offered minimal sound amplification. Wouldn’t it be amazing if an intervention as simple as hearing aids could change the course of Alzheimer’s? But alas, there appeared to be no effect on function, behavior or even quality of life measures. As a recent World Health Organization review concluded, “There is insufficient evidence to recommend use of hearing aids to reduce the risk of cognitive decline and/or dementia.” If they help with symptomatic relief of hearing difficulty, great, but what about treating the cause of hearing loss in the first place? We’ll address that very question, next.