A forthcoming study in the Journal of the American Medical Association Internal Medicine found that hearing loss was associated with accelerated cognitive decline in a sample of community-dwelling older adults. This longitudinal study (in which observations are repeated at different points over time) builds on earlier cross-sectional studies (in which observations are made at one point in time), some discussed previously in aging in action. that identified a correlation between hearing loss and cognitive impairment.
The 1,984 study participants were drawn from a larger longitudinal study, which began in 1997, of a random sample of older adults from the Pittsburgh and Memphis metropolitan areas. As part of the inclusion criteria for the hearing study, participants had to report no difficulty with basic activities of daily living and to be without significant cognitive impairment at the time they began the study. Participants were given a hearing test and were then given cognitive tests at as many as four different times over the following six years. Participants were also given a questionnaire and health screenings for other relevant risk factors for cognitive decline, such as hypertension, diabetes mellitus, stroke history, and smoking status.
Participants had their hearing assessed in a “sound-treated booth” in a laboratory, which allows for a more controlled and stable environment than many previous studies on hearing and cognition, which have tended to use portable equipment in participants’ homes.
On average, participants with hearing loss at the beginning of the study experienced more rapid cognitive decline than participants without hearing loss. Severity of hearing loss as also associated with the rapidness of decline, and with the chance of developing clinically significant cognitive impairment. The study was not designed to explain the underlying causes behind this association; various hypotheses include an underlying neurological disorder influencing both hearing and cognitive test performance, the possibility that hearing loss leads to social isolation or “cognitive load” (that is, the loss of hearing puts a sufficient burden on the individual, negatively impacting their other cognitive abilities), and the possibility that cognitive testing may be biased against individuals with hearing loss who might experience poor verbal communication. However, both verbal and nonverbal test scores were associated with hearing loss within this sample.
Hearing aid use appeared to decrease the rates of cognitive decline among those with hearing impairments, though not to a standard of statistical significance. However, the subsample of individuals with hearing aids may not have been large enough to detect protective effects of hearing aid use. Further, individuals with hearing aids differ tremendously in their experience of the technology, in terms of treatment and hearing efficacy. Thus, it is unclear from this study whether or not successful hearing aid use might attenuate the association between hearing loss and cognitive decline.