Hearing loss in middle age may accelerate cognitive decline

A study conducted in Brazil on 805 people in their 50s confirmed that those with hearing loss had an increased risk of cognitive decline. The results, published in the Journal of Alzheimer’s Disease, point to the need for greater attention to hearing health as a way to prevent dementia.

“Hearing loss is what we call a modifiable risk factor for dementia, including Alzheimer’s, precisely because it can be detected and corrected. By 2050, more than 70% of people with dementia are expected to live in low- and middle-income countries like Brazil. That’s why it’s important to have studies that identify our reality and the factors that can be prevented. In addition to the individual burden, there’s also a collective burden. There’s no way that Brazil and other low- and middle-income countries can grow old with dementia,” said Claudia Suemoto, professor at the University of São Paulo’s Medical School (FM-USP) and author of the study.

The research was conducted as part of the Longitudinal Study of Adult Health (ELSA-Brazil), which has been monitoring data from 15,000 public servants from six universities and research centers in the country since 2008. The initiative is funded by the Ministry of Health and the National Council for Scientific and Technological Development (CNPq), linked to the Ministry of Science, Technology and Innovation (MCTI). The audiological assessment and its comparison with the data on cognition collected by ELSA-Brazil were supported by FAPESP.

Mechanisms

Hearing loss usually begins in middle age and is a recognized risk factor for dementia. According to Suemoto, this occurs through two mechanisms. The first is that hearing is an important input pathway for information to the brain. “It depends on input pathways to deliver a response, along with the knowledge it’s already acquired. However, when a pathway is interrupted, important areas are no longer stimulated, which can accelerate cognitive decline,” she explains. 

The second mechanism is behavioral: hearing loss tends to lead to social isolation. “Almost everyone knows someone older, be it a friend or relative, who doesn’t hear well. To talk to them, you have to speak louder, repeat sentences and they end up being excluded from conversations. In a way, it’s so hard for them to hear that they shut themselves out, lose interest and move away. So there’s also the mechanism of social isolation, which is another recognized risk factor for dementia,” she says.

In the study, the participants underwent audiometry tests, an objective measure of hearing quality, three times over the course of the eight-year study. Tests of memory, language and executive function were carried out during the same period to measure the association between hearing loss and significant cognitive decline. Of the 805 participants, 62 (7.7%) had hearing loss. After eight years of follow-up, these individuals had faster overall cognitive decline than expected for their age. In addition, specific cognitive tests showed similar but less precise declines in memory, verbal fluency and executive function.

“This shows that it’s important to do an audiometry test because it usually takes a while for people to become aware of their hearing deficit. They start to hear badly, but they don’t realize it and adapt to the new situation. But knowing that there’s a loss, it’s possible to correct it with the use of hearing aids. And you also have to remove the stimulus that’s causing the problem,” she warns. 

According to the researcher, the main causes of hearing loss in middle age are work-related. “There are different types of jobs that involve a lot of noise. These people need to wear protective equipment to reduce hearing loss. There’s also the problem of using headphones at too high a volume. All of this is detrimental, so it’s important to get the problem diagnosed,” she adds.

In addition to hearing loss, says the researcher, there are 11 other potential modifiable risk factors for dementia: low education, hypertension, brain damage, diabetes, obesity, alcoholism, smoking, depression, sedentary lifestyle, air pollution and social isolation.

About FAPESP

The São Paulo Research Foundation (FAPESP) is a public institution with the mission of supporting scientific research in all fields of knowledge by awarding scholarships, fellowships and grants to investigators linked with higher education and research institutions in the state of São Paulo, Brazil. FAPESP is aware that the very best research can only be done by working with the best researchers internationally. Therefore, it has established partnerships with funding agencies, higher education, private companies, and research organizations in other countries known for the quality of their research and has been encouraging scientists funded by its grants to further develop their international collaboration.