April 7 (UPI) -- Older adults who experience both hearing and vision loss are more than twice as likely to develop dementia as they age, according to a study published Wednesday by the journal Neurology.
However, no link was found between dementia and losing just one of the two senses, the researchers said.
Roughly 8% of adults with both hearing and vision loss in the study developed dementia, compared with less than 3% of those with one impairment or no impairment.
"Depending on the degree of hearing or vision loss, losing function in your senses can be distressing and have an impact on your daily life," study co-author author JinHyeong Jhoo said in a press release.
"But our study results suggest losing both may be of particular concern," said Jhoo, a researcher at Kangwon National University School of Medicine in Chuncheon, South Korea.
About 6 million adults in the United States have some form of dementia, which can be caused by brain damage from strokes, concussions, neurological disorders or infections, but also can run in families, according to the Alzheimer's Association.
Although it's unlikely that loss of sight and hearing causes dementia, it's possible that losing both senses causes older adults to limit social activities, exercise and other activities, such as reading, that help maintain cognitive function. All have been shown in previous research to reduce dementia risk.
For this study, Jhoo and colleagues assessed more than 6,500 adults age 58 to 101 for visual and hearing impairment, which was determined based on responses to a questionnaire asking about using glasses or hearing aids.
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,"
Participants 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."
Participants' thinking and memory skills were also evaluated every two years for six years using a test that includes word recall and recognition, according to the researchers.
At the beginning of the study, about 14% of participants had normal eyesight and hearing, 45% had either visual or hearing impairment and 40% said they had both.
At 8%, dementia was more than twice as common in the group with both impairments at the beginning of the study than in those with one sensory impairment, 2.4%, or no sensory impairment, 2.3%.
During the six-year follow-up period, 7.4% of the participants with both impairments developed dementia, compared with 2.9% of those one impairment and 1.8% of those with no impairments.
In addition, 11% of 142 people who could not determine whether they had a sensory impairment developed dementia.
"Older people with only a visual or hearing impairment can usually still maintain social contact, so they may not feel be as isolated or depressed as people who have both impairments," Jhoo said.
"However, when someone has both impairments, that may increase the risk of isolation and depression, which previous research has found may affect dementia risk and thinking skills later on," the researcher said.