Preventing hearing loss key to dementia protection

Hearing aids do not appear to slow the cognitive decline associated with hearing loss.

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A large study has bolstered the association between hearing loss and cognitive decline, further finding that hearing aids do not appear to slow impairment.

Hearing aids should still be prescribed to mitigate social isolation and improve quality of life, but not for cognitive protection, say the authors of the study, published in JAMA Network Open.

The Lancet commission on dementia prevention has found hearing loss to be the single biggest modifiable risk factor for dementia, potentially accounting for 8% of cases, and recommends hearing aids for protection. In its 2024 update it says use of hearing aids “appears to be particularly effective in people with hearing loss and additional risk factors for dementia”.

But the evidence is mixed, the authors of the new study say: a 2022 meta-analysis cited by the commission found in favour of hearing aid use to protect cognition, but that finding depended heavily on a single study. Only one randomised controlled trial appears to have been done, they say, and that found a benefit only for those at high risk of cognitive decline.

Using the large French CONSTANCES cohort the authors extracted a representative sample of over 62,000 people aged 45-69 who had their hearing and cognition evaluated. Fifty per cent had normal hearing, 38% had mild hearing loss, 10% had disabling loss without hearing aids and 3% used hearing aids.

The proportion with global cognitive impairment increased with level of hearing loss: 16% among participants with normal hearing, 27% for mild hearing loss and 37% for disabling hearing loss. Among those using hearing aids the proportion was 34%.

The overall association was only slightly weaker when covariates – BMI, diabetes, blood pressure, depression, CVD, socioeconomic status, smoking, education and noise exposure at work – were taken into account.

The team adjusted for possible confounding by indication in the hearing aids group. Even after that, the only group for whom hearing aids offered protection was people with depression.

“A synergistic beneficial association of HA [hearing aid] use with social isolation caused by both depression and auditory deprivation might explain this finding,” the authors say.

Potential mechanisms for the association include social isolation, “cognitive resource redistribution toward auditory perceptual processing, cognitive decline resulting from prolonged auditory input deprivation, and shared neurodegenerative processes in the aging brain associated with both cognitive deterioration and HL [hearing loss]”.

Hearing loss may also be a risk factor for temporal lobe volume loss and decline in the hippocampus and entorhinal cortex, they say.

“Altogether, the present findings combined with prior evidence support that patients with HL are at higher risk of cognitive impairment …

“Furthermore, HA prescription in patients with disabling HL should be guided by their established benefits on quality of life and social isolation, but not to mitigate cognitive decline, for which further research is needed.”

Associate Professor Michael Woodward AM, geriatrician and honorary medical adviser to Dementia Australia, told TMR there were a number of possible explanations for the lack of evidence of benefit for hearing aids. The study did not record how long the hearing loss had gone on for or whether people actually used their hearing aids or how much.

“Even if it doesn’t help to reduce your risk of dementia, there are many other good reasons for wearing hearing aids, including remaining socially active,” he said.

What was more important, he said, was the confirmation of hearing loss as a risk factor for dementia. That meant prevention was crucial: by wearing ear protection at noisy locations, making sure children’s ear infections were properly treated, removing ear wax and so on.

“It’s the largest potentially avoidable risk factor,” he said. “We’ve got 421,000 Australians with dementia at the moment, rising to nearly 900,000 by 2055, and twice as many people with mild cognitive impairment, and also probably another type of many people whose brains are already [building up amyloid and tau].

“So there’s an awful lot of people out there potentially going to end up with dementia, and if we can reduce it, what a great thing that would be.”

JAMA Network Open, 1 October 2024