Emerging science shows that sensory dysfunction can increase the risk of dementia, and the new research presented at AAIC 2019 further demonstrates the impact of multiple co-occurring sensory impairments.
Research from the University of Washington School of Public Health showed that impairment of either vision or hearing increases the risk of developing dementia, and that impairment in both senses further increases those odds. Meanwhile, researchers at the University of California, San Francisco studied the combined effects of loss of smell, touch, vision and hearing; they found that even mild impairments in multiple senses were associated with an increased risk of dementia and cognitive decline.
We're beginning to learn through these new research findings that sensory impairments, even those that are very mild, may also be associated with increased risk of dementia, especially when there are several of them at the same time. We need more research to confirm these initial findings and to see if correcting the sensory impairments can reduce dementia risk."
Maria C. Carrillo, PhD, Alzheimer's Association chief science officer
Combined visual and hearing impairment increases risk of dementia in older adults
While recent studies have shown that loss of sensory function increases risk of developing dementia, very little is known about the impact of co-occurring sensory impairments. In order to understand the effect of dual sensory impairment on the development of dementia, Phillip Hwang, MPH, a doctoral epidemiology student at the University of Washington, and colleagues examined the association between hearing and vision impairment and risk of Alzheimer's or other dementia in 2,051 people from the Ginkgo Evaluation of Memory Study aged 75 or older who did not have dementia at the time of study enrollment.
Baseline sensory impairment was established through self-reported responses to a set of questions on hearing and vision. Over seven years of follow-up, incident dementia was assessed based on clinical diagnosis using DSM-IV criteria, and Alzheimer's disease was determined using criteria developed by the National Institute of Neurological and Communicative Disorders and Stroke — Alzheimer's Disease and Related Disorders Association (NINCDS-ADRDA; the ADRDA is now known as the Alzheimer's Association).
The researchers found that the number of sensory impairments was associated with risk of all-cause dementia and Alzheimer's disease (both p≤0.01) in a graded fashion. Having either visual or hearing impairment increased the risk of developing dementia by 11% and Alzheimer's by 10%. Having both visual and hearing impairment raised the risk of developing dementia by 86% and Alzheimer's by 112%.
"These findings suggest that co-occurring hearing and vision problems in late-life are strongly associated with increased risk of all-cause dementia and Alzheimer's dementia," said Hwang. "Impairment of more than one sense seems to increase risk of dementia synergistically."
"Assessment of visual and hearing function may help identify older adults at high risk of developing dementia," Hwang added.
Even mild multisensory impairment is associated with dementia and cognitive decline
Willa D. Brenowitz, PhD, MPH, a postdoctoral researcher at the University of California, San Francisco, working with Kristine Yaffe, MD, and colleagues conducted a study of impairments in vision, hearing, smell and touch to investigate the effect of multisensory impairment on dementia risk.
The researchers studied a group of 1,810 older Americans aged 70-79 from the Health, Aging and Body Composition Study who did not have dementia at the time of enrollment. They assessed sight, hearing, touch and smell to create a summary multisensory function score for each participant. Incident dementia over 10 years was assessed using a combination of hospitalization records, anti-dementia medication prescriptions and cognitive decline as measured by the Modified Mini-Mental State Exam (3MS).
The researchers found that participants with lower sensory function scores — thus, greater levels of impairment — had significantly increased risk of both dementia and cognitive decline (both p<0.001). Risk of dementia was nearly seven times greater for those participants in the lowest scoring quarter of sensory function in the study population compared with those in the highest scoring quarter.
However, even mild impairment in multisensory functioning was strongly associated with these risks. A four-point difference in score (out of 12 points) was associated with a 68% higher risk for dementia (95% CI: 31%, 101%) and an annual decline of 0.24 points on the 3MS (95% CI: 0.36, 0.12 points).
"Our findings suggest that testing for changes in multisensory function may help identify those at high risk for dementia," Brenowitz said. "Sensory function in multiple domains can be measured during routine health care visits using non-invasive or minimally invasive tests. In addition, some forms of hearing and vision loss can be treated or corrected, which provides potential opportunities for intervention. However, we need more research to determine if treatment or prevention of sensory impairments could reduce risk of dementia."
Results from the two studies reported at AAIC 2019 demonstrate that sensory impairment, particularly across multiple senses, is strongly associated with an increased risk of developing dementia or Alzheimer's disease. The findings suggest that assessment of sensory function by clinicians and caregivers should play an important role in diagnosis and care of older adults and those at risk of developing these diseases.