A hypothetical intervention on the use of hearing aids for the risk of dementia in people with hearing loss in UK Biobank.

Observational studies have reported that hearing aid (HA) use is associated with a reduced risk of dementia diagnosis, suggesting a possible protective effect. However, extant observational studies do not explicitly model causal effects, while randomised controlled trials on the effect of HA on dementia exhibit short follow-up. Here we used self-report, hearing tests, and healthcare records in UK Biobank to design a hypothetical intervention for the effect of HA use on the risk of dementia diagnosis in people with incident hearing loss (HL). HA users exhibited a higher risk of dementia diagnosis than non-users (RR=1.43, 95%CI=1.08-1.88). Associations between HA use and dementia diagnosis were robust across sensitivity analyses (RRs: 1.34-1.59) but adjustment for primary healthcare utilisation (0.77, 0.44-1.33) or primary and secondary care utilisation (0.68, 0.39-1.18) substantially decreased the observed effect. The decrease in effect estimates upon adjustment for primary (1.30, 0.95-1.78) and primary and secondary healthcare utilisation (1.30, 0.94-1.78) was smaller when participants with relatively early diagnoses of HL were included in the sample compared to when they were not. While the findings are not conclusive, they suggest residual confounding by healthcare utilisation and dating of HL diagnosis in participants without primary care data in UK Biobank.