Responsible scientists and scholars hesitate to prematurely claim causation when data shows a correlation between two factors. Researchers from the University of Oxford Nuffield Department of Population Health withhold claims of causation in either direction between speech-in-noise (SiN) hearing impairment and dementia. In a recently published study in Alzheimer’s & Dementia: The Journal of the Alzheimer’s Association, the Oxford authors point to the study’s limitations and suggest directions for further inquiry and research.
One cannot read the study and the related Oxford news coverage, however, without concluding that the association between SiN difficulty and dementia is too strong to ignore. There’s something there. Even if there’s only a slight chance that treating hearing loss could stop or slow the course of developing dementia, prudence suggests we should do so.
The UK research followed 82,039 men and women age 60 and above during an 11-year period. The subjects were all dementia-free at the start of the study. Oxford researchers tested each of the participants for their ability to understand speech against a background of white noise. The participants’ SiN hearing status at the time was graded normal (67,645 people), insufficient (11,239), or poor (3,065). The initial test also surveyed symptoms of depression, social isolation, hearing aid use, and self-reported hearing impairment. The researchers followed-up by checking for dementia in hospital inpatient and death records. A total of 1,285 subjects developed dementia during the study period. There were 896 cases of dementia among those people originally evaluated with normal SiN hearing, 286 cases among those with insufficient SiN status, and 103 cases from the poor SiN group.
Statistical analysis of the Oxford study results found that people with insufficient SiN hearing were at a 61% greater risk of developing dementia than those with normal hearing. Subjects with poor SiN hearing had a 91% higher risk. The researchers did not find significant evidence that social isolation or depression made a difference in the relationship between SiN hearing loss and dementia. The study authors reported that the numbers were too small for statistical significance, but that the association between hearing loss and dementia was lower among subjects who wore hearing aids.
While calling out their study’s limitations, the Oxford researchers call for further research that integrates tests of both SiN hearing and pure tone hearing, in hopes of determining whether age-related hearing impairment is a modifiable risk factor for dementia. Also, because dementia develops slowly, reverse causation may be at play; dementia may cause SiN hearing impairment.
While we can’t draw definite conclusions from the Oxford study, we can suggest that taking steps to compensate for hearing impairment may do more than help you understand conversation in a crowded room.
