There is an intuitive logic to the idea that decreased sensory input would worsen cognitive decline. As 47 million adults currently live with dementia, and that number is expected to triple by the year 2050, understanding this idea could be a public health boon. If we can define the relationship between impaired sensory input and dementia, we can then create interventions to slow the process of cognitive decline.
This is what researchers from Harvard Medical School assessed in a study published online in Alzheimer’s and Dementia. Specifically, they assessed the relationship between hearing loss and subjective cognitive functioning.
The 8-year, longitudinal study followed over 10,000 men aged 62 or older. The subjects reported their hearing concerns at the onset of the study. They then self-reported their cognitive concerns at the end of years 2, 4 and 8. At least one new concern between reports on a six-item checklist was considered a decline.
Patients were broken into groups with normal hearing or mildly-, moderately-, or severely-impaired hearing. Those who used hearing aids were also considered separately.
The results showed a correlation with the severity of hearing loss and subjective cognitive decline:
- Patients with mild hearing impairment at study onset had an adjusted relative risk of 1.30 for cognitive decline.
- Patients with moderate hearing impairment at study onset had an adjusted relative risk of 1.42 for cognitive decline.
- Patients with severe hearing impairment at study onset had an adjusted relative risk of 1.54 for cognitive decline.
- However, those with severe hearing loss who used hearing aids had a lower relative risk, 1.37, than their counterparts who did not.
This study looked at subjective cognitive functioning as its endpoint. As patients may notice limitations in cognitive performance before any deficits are evident on formal evaluation tools, this can serve as a preclinical marker for dementia.
While the pathophysiology responsible for the relationship has not been established, the authors state, “Hearing loss-related degradation or deprivation of sound stimuli may lead to more effortful listening, increased cognitive load, and alterations in neural networks.” In other words, resources might be channeled into interpreting auditory input and become unavailable for other cognitive tasks.
The study is limited by the inclusion of elderly white males of higher socioeconomic status, making further study in women and other populations needed. In addition, the study was observational, but results were “robust to adjustments for numerous potential cofounders.”
With the rising age of the population and the increased incidence of dementia, this study adds a significant piece of evidence for the role of hearing in the process of declining cognitive function. There is much to be learned about how sensory impairment affects the development and course of dementia, but it seems prudent—even intuitive—to encourage use of hearing aids as early as possible after onset of hearing impairment.