Losing hearing in middle age may increase dementia risk

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Hearing loss in middle age is associated with higher odds of cognitive decline and dementia in later years, Reuters Health reports a large study in Taiwan suggests. Researchers tracked more than 16,000 men and women and found that a new diagnosis of hearing loss between ages 45 and 65 more than doubled the odds of a dementia diagnosis in the next dozen years.

Even mild levels of hearing loss could be a risk factor, so hearing protection, screening and hearing aids may be important means of reducing cognitive risk as well, the study team writes. “Hearing loss is a potential reversible risk factor for dementia, including Alzheimer’s disease,” said senior study author Charles Tzu-Chi Lee of National Taiwan Normal University in Taipei.

Past research suggests that about two thirds of the risk for dementia is hereditary or genetic, which means about one third of the risk is from things that are modifiable, Lee noted. Among modifiable risk factors, hearing loss accounts for about 9% of dementia risk, a greater proportion than factors like hypertension, obesity, depression, diabetes and smoking. “The early identification of hearing loss … and successful hearing rehabilitation can mitigate the negative effects of hearing loss,” Lee is quoted in the report as saying. “However, the ideal time to perform hearing loss screening to reduce the risk of dementia remains unclear.”

Lee and colleague Chin-Mei Liu of the Taiwan Centres for Disease Control analysed data on people aged 45 and older from the National Health Insurance Research Database of Taiwan. They matched 8,135 patients newly diagnosed with hearing loss between 2000 and 2011 to 8,135 similar individuals without hearing loss and followed them all through 2013. All were free of dementia at the start, but over time, 1,868 people developed dementia – and 59% of them came from the hearing loss group.

Among people with hearing loss, new dementia cases were identified at a rate of 19 per 10,000 people, compared with 14 per 10,000 without hearing loss. Overall, hearing loss was associated with a 17% risk increase for dementia, the researchers calculated.
But when they looked at subsets of people, almost all the increased risk was concentrated in the youngest age group. Among those 45-65, dementia risk was 2.21-fold higher with hearing loss.

“The present study suggests that screening for hearing loss should be performed when people are middle aged,” Lee said.

The report says the results factored in variables such as sex, age and insurance type, as well as other known risks for cognitive decline and dementia. Among these, six other conditions were associated with an increased risk of dementia: cerebrovascular disease, diabetes, anxiety, depression, alcohol-related illnesses and head injury.

The study was not designed to determine how hearing loss might contribute to dementia, or if the two conditions share the same cause. One limitation of insurance data, the researchers note, is lack of precision in the dementia diagnoses.

“In an ageing population, dementia will present one of the greatest challenges to society in this century,” said David Loughrey of the Trinity College Institute of Neuroscience in Dublin, who wasn’t involved in the study. “There are now more people over the age of 65 than under the age of 5 for the first time in human history,” he said in the report. “Pharmacological treatments for the most common cause of dementia, Alzheimer’s disease, only offer symptom-modifying effects. This has led to suggestions that a change in approach to prevention rather than treatment after diagnosis may be more beneficial.”

Future studies will investigate whether treating hearing loss can decrease the risk of dementia, the study team writes.

Abstract
Importance: Hearing loss (HL) may be a modifiable risk factor for dementia, and longitudinal studies are needed to examine the association of HL and dementia.
Objective: To investigate the association of HL with incident dementia in Taiwanese adults in the general population.
Design, Setting, and Participants: This population-based cohort study collected data from the National Health Insurance Research Database of Taiwan. Patients newly diagnosed with HL from January 1, 2000, through December 31, 2011 (n = 8135), constituted the exposed (HL) group. The HL group patients were matched by sex, age, residence, and insurance premium to individuals without HL (non-HL group) (n = 8135). Data were analyzed from January 1, 2000, to December 31, 2013.
Exposure: Hearing loss defined according to International Classification of Diseases, Ninth Revision, Clinical Modification (ICD-9-CM) codes.
Main Outcomes and Measures: Dementia classified according to ICD-9-CM codes.
Results: Of a total of 16 270 participants (9286 [57.1%] men; mean [SD] age, 65.2 [11.1] years), 1868 developed dementia. The dementia incidence rate in the HL group was higher than that in the non-HL group (19.38 [95% CI, 18.25-20.57] per 1000 person-years vs 13.98 [95% CI, 13.01-15.00] per 1000 person-years) during the follow-up period. In the fully adjusted multivariate Cox proportional hazards regression model applied for risk analysis, patients with HL had a significant risk of dementia (hazard ratio [HR], 1.17; 95% CI, 1.07-1.29; false discovery rate [FDR] P = .003). Subgroup analysis revealed that, among 3 age groups (45-64, 65-74, and ≥75 years), the group aged 45 to 64 years was associated with a risk of dementia (HR, 2.21 [95% CI, 1.57-3.12]; FDR P < .001). In sensitivity analysis, the presence of HL among those aged 45 to 64 years (HR, 1.40; 95% CI, 1.12-1.75; FDR P = .01) was associated with a risk of dementia.
Conclusions and Relevance: In this study, hearing loss was positively associated with a risk of dementia, especially in patients aged 45 to 64 years. Hearing protection, screening, and treatment may be used as strategies for mitigating this potential risk factor.

Authors
Chin-Mei Liu; Charles Tzu-Chi Lee

Reuters Health report
JAMA Network Open abstract


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