The combination of hearing loss and vision loss is linked to an eightfold increased risk of cognitive impairment, new research shows.

Investigators analyzed data on more than 5 million US seniors. Adjusted results show that participants with hearing impairment alone had more than twice the odds of also having cognitive impairment, while those with vision impairment alone had more than triple the odds of cognitive impairment.

However, those with dual sensory impairment (DSI) had an eightfold higher risk for cognitive impairment.

In addition, half of the participants with DSI also had cognitive impairment. Of those with cognitive impairment, 16% had DSI, compared with only about 2% of their peers without cognitive impairment.

“The findings of the present study may inform interventions that can support older people with concurrent sensory impairment and cognitive impairment,” lead author Esme Fuller-Thomson, PhD, professor, Factor-Inwentash Faculty of Social Work, University of Toronto, Canada, told Medscape Medical News.

“Special attention, in particular, should be given to those aged 65 to 74 who have serious hearing and/or vision impairment [because], if the relationship with dementia is found to be causal, such interventions can potentially mitigate the development of cognitive impairment,” said Fuller-Thomson, who is also director of the Institute for Life Course and Aging and a professor in the Department of Family and Community Medicine and Faculty of Nursing, all at the University of Toronto.

The findings were published online May 2 in the Journal of Alzheimer’s Disease  Reports.

Sensory Isolation

Hearing and vision impairment increase with age; it is estimated that one third of US adults between the ages of 65 and 74 experience hearing loss, and 4% experience vision impairment, the investigators note.

“The link between dual hearing loss and seeing loss and mental health problems such as depression and social isolation have been well researched, but we were very interested in the link between dual sensory loss and cognitive problems,” Fuller-Thomson said.

Additionally, “there have been several studies in the past decade linking hearing loss to dementia and cognitive decline, but less attention has been paid to cognitive problems among those with DSI, despite this group being particularly isolated,” she said.

Existing research into DSI suggests an association with cognitive decline; the current investigators sought to expand on this previous work.

To do so, they used merged data from 10 consecutive waves from 2008 to 2017 of the American Community Survey (ACS), which was conducted by the US Census Bureau. The ACS is a nationally representative sample of 3.5 million randomly selected US addresses and includes community-dwelling adults and those residing in institutional settings.

Participants aged 65 or older (n = 5,405,135; 56.4% women) were asked yes/no questions regarding serious cognitive impairment, hearing impairment, and vision impairment. A proxy, such as a family member or nursing home staff member, provided answers for individuals not capable of self-report.

Potential confounding variables included age, race/ethnicity, sex, education, and household income.

Potential Mechanisms

Results showed that among those with cognitive impairment, there was a higher prevalence of hearing impairment, vision impairment, and DSI than among their peers without cognitive impairment; in addition, a lower percentage of these persons had no sensory impairment (P < .001).

The prevalence of DSI climbed with age, from 1.5% for respondents aged 65 to 74 years to 2.6% for those aged 75 to 84 and to 10.8% in those 85 years and older.

Individuals with higher levels of poverty also had higher levels of DSI. Among those who had not completed high school, the prevalence of DSI was higher compared with high school or university graduates (6.3% vs 3.1% and 1.85, respectively).

After controlling for age, race, education, and income, the researchers found “substantially” higher odds of cognitive impairment in those with vs those without sensory impairments.

“The magnitude of the odds of cognitive impairment by sensory impairment was greatest for the youngest cohort (age 65 – 74) and lowest for the oldest cohort (age 85+),” the investigators write. Among participants in the youngest cohort, there was a “dose-response relationship” for those with hearing impairment only, visual impairment only, and DSI.

Because the study was observational, it “does not provide sufficient information to determine the reasons behind the observed link between sensory loss and cognitive problems,” Fuller-Thomson said. However, there are “several potential causal mechanisms [that] warrant future research.”

The “sensory deprivation hypothesis” suggests that DSI could cause cognitive deterioration because of decreased auditory and visual input. The “resource allocation hypothesis” posits that hearing- or vision-impaired older adults “may use more cognitive resources to accommodate for sensory deficits, allocating fewer cognitive resources for higher-order memory processes,” the researchers write. Hearing impairment “may also lead to social disengagement among older adults, hastening cognitive decline due to isolation and lack of stimulation,” they add.

Reverse causality is also possible. In the “cognitive load on perception” hypothesis, cognitive decline may lead to declines in hearing and vision because of “decreased resources for sensory processing.”

In addition, the association may be noncausal. “The ‘common cause hypothesis’ theorizes that sensory impairment and cognitive impairment may be due to shared age-related degeneration of the central nervous system…or frailty,” Fuller-Thomson said.

Parallel Findings

The results are similar to those from a study conducted by Phillip Hwang, PhD, Department of Anatomy amd Neurobiology, Boston University School of Medicine, Massachusetts, and colleagues that was published online May 5 in JAMA Network Open.

They analyzed data on 8 years of follow-up of 2927 participants in the Cardiovascular Health Study (mean age, 74.6 years; 58.2% women).

Compared with no sensory impairment, DSI was associated with increased risk for all-cause dementia and Alzheimer’s disease (AD), but not with vascular dementia.

“Future work in health care guidelines could consider incorporating screening of sensory impairment in older adults as part of risk assessment for dementia,” Nicholas Reed, AuD, Johns Hopkins University Bloomberg School of Public Health, and Esther Oh, MD, PhD, Johns Hopkins University School of Medicine, Baltimore, Maryland, write in an accompanying editorial.

Accurate Testing

Commenting on both studies for Medscape Medical News, Heather Whitson, MD, professor of medicine (geriatrics) and ophthalmology and director at the Duke Center for the Study of Aging and Human Development, Durham, North Carolina, said both “add further strength to the evidence base, which has really converged in the last few years to support that there is a link between sensory health and cognitive health.”

However, “we still don’t know whether hearing/vision loss causes cognitive decline, though there are plausible ways that sensory loss could affect cognitive abilities like memory, language, and executive function,” she said

Whitson, who was not involved with the research, is also co-director of the Duke/UNC Alzheimer’s Disease Research Center, Duke University School of Medicine, and the Durham VA Medical Center.

“The big question is whether we can improve patients’ cognitive performance by treating or accommodating their sensory impairments,” she said. “If safe and feasible things like hearing aids or cataract surgery improve cognitive health, even a little bit, it would be a huge benefit to society, because sensory loss is very common, and there are many treatment options,” Whitson added.

Fuller-Thomson emphasized that practitioners should “consider the full impact of sensory impairment on cognitive testing methods, as both auditory and visual testing methods may fail to take hearing and vision impairment into account.”

Thus, “when performing cognitive tests on older adults with sensory impairments, practitioners should ensure they are communicating audibly and/or using visual speech cues for hearing impaired individuals, eliminating items from cognitive tests that rely on vision for those who are visually impaired, and using physical cues for individuals with hearing or dual sensory impairment, as this can help increase the accuracy of testing and prevent confounding,” she said.

The study by Fuller-Thomson et al was funded by a donation from Janis Rotman. Its investigators have reported no relevant financial relationships. The study by Hwang et al was funded by contracts from the National Heart, Lung, and Blood Institute, the National Institute of Neurological Disorders and Stroke, and the National Institute on Aging. Hwang reports no relevant financial relationships. The other investigators’ disclosures are listed in the original article. Reed received grants from the National Institute on Aging during the conduct of the study and has served on the advisory board of Neosensory outside the submitted work. Oh and Whitson report no relevant financial relationships.

J Alzheimers Dis Rep. Published online May 2, 2022. Full article

JAMA Netw Open. Published online May 5, 2022. Full article, Edtorial

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