By Linda Carroll
(Reuters Health) - Impairment of both vision and hearing may double the risk of dementia in older adults, a new study suggests.
An analysis of data from more than 6,500 seniors who were followed for six years revealed that losing both senses, but not one, was significantly associated with dementia incidence during follow-up (hazard ratio 1.9), researchers report in Neurology.
"Visual and hearing impairments are known risk factors for cognitive decline," said study coauthor Dr. Jin Hyeong Jhoo, a professor in the department of psychiatry at the Kangwon National University School of Medicine, in Chuncheon, South Korea.
"However, the research results are inconsistent," Dr. Jhoo said in an email. "In this study the incidence of dementia did not increase with single sensory impairment, but with dual sensory impairment. This explains the inconsistent results of previous studies. Moreover, the objective neuropsychological test score decreased significantly over time only in the group with dual sensory impairment. This shows that dual sensory impairment plays an important role not only in the onset of dementia, but also in overall decline."
Dr. Jhoo suspects that depression and social isolation may play a role in connecting dual sensory loss with dementia.
"Elderly people with dual sensory impairment are more likely to have depression and are more susceptible to social isolation than elderly individuals with normal sensory functions," he added. "These were previously known as factors that increase the risk of dementia. In addition, degenerative changes in the brain are accelerated as sensory input to the brain decreases owing to sensory deprivation, which can be a potential mechanism for the findings of this study."
To look at the potential impact of dual sensory loss, Dr. Jhoo and his colleagues included data on 6,520 adults participating in a nationwide longitudinal cohort who were between the ages of 58 and 101 at the start of the study period. Visual and hearing impairment were assessed through questionnaires that asked how well people saw and heard. Participants rated their hearing as "normal," "reduced, but able to communicate without a hearing aid," "difficult communicating with a hearing aid," or "no hearing at all." They rated their sight as "normal," "reduced, but able to view newspaper or TV without wearing glasses," "unable to view newspaper or TV with glasses" or "no sight at all."
At the study outset, 932 of the participants had normal hearing and sight, 2,957 had either visual or hearing impairment, and 2,631 said both senses were impaired. Demographic and clinical variables, including cognitive outcomes were evaluated every two years over six years.
At baseline, double sensory impairment was significantly associated with increased dementia prevalence compared to normal sensory function (odds ratio 2.17), but single sensory impairment was not (OR 1.7). Over the six years of follow-up the incidence of dementia was significantly higher in the dual sensory group than in those without impairments, but this was not seen in the single-impairment group (HR 1.21).
The findings underscore the importance of correcting vision with glasses or surgery and hearing through hearing aids or surgery, Dr. Jhoo said. No previous study has looked at the impact of improvements in both vision and hearing, he said, adding that this would be a good topic to explore.
The new study is "really interesting," said Dr. Avnish Deobhakta, an assistant professor of ophthalmology at the Icahn School of Medicine at Mount Sinai and the New York Eye and Ear Infirmary of Mount Sinai, in New York City.
"While I'm primarily focused on vision this new study shows that it's important for our field and others to take into account the fact that all these senses work in tandem," he added.
If a patient has vision problems that might be corrected by surgery, knowing that the patient also has hearing problems might tip the risk-benefit ratio in favor of the operation, Dr. Deobhakta said.
SOURCE: https://bit.ly/3uw3Ljj Neurology, online April 7, 2021.