Hearing Loss Tied to Cognitive Decline, Aids of Little Help

Hearing loss is associated with an increased risk of subsequent cognitive decline, in a dose-dependent manner, new research shows.

In a large longitudinal study of more than 10,000 men, investigators found that compared to their counterparts with no hearing loss, the risk of subjective cognitive decline was 30% higher among men with self-reported mild hearing loss and 42% to 54% higher among those with moderate or worse hearing loss.

"Our findings show that hearing loss is associated with new onset of subjective cognitive concerns, which may be indicative of early stage changes in cognition and on a continuum with clinical manifestations of mild cognitive impairment and dementia," principal investigator Sharon G. Curhan, MD, of the Channing Division of Network Medicine and the Department of Medicine at Brigham and Women's Hospital/Harvard Medical School in Boston, told Medscape Medical News.

"These findings may help identify individuals at greater risk of cognitive decline and reveal a valuable opportunity for earlier treatment interventions that could be more effective than treatment of later stage dementia," she added.

The study was published online January 29 in Alzheimer's & Dementia.

Conflicting Findings

"The prevalence of hearing loss increases with age and men are affected more frequently than women. Approximately one-third of men aged 40 years and older have hearing loss," the investigators note.

"Understanding whether hearing loss may influence early cognitive decline could reveal a valuable opportunity for identifying determinants of early cognitive decline and provide crucial insights for earlier intervention and prevention," they write.

They also note that studies examining hearing aid use and whether it mitigates the risk of cognitive decline have produced conflicting findings.

To examine the relationship between self-reported hearing loss, hearing aid use, and the risk of subjective cognitive function (SCF), the investigators conducted an 8-year longitudinal study in a cohort of 10,107 from the Health Professionals Follow-up Study (HPFS).

The HPFS is a prospective cohort study that enrolled 51,529 male dentists, optometrists, osteopaths, pharmacists, podiatrists, and veterinarians who were 40 to 75 years old at the start in 1986.

The 10,107 participants included in the analysis reported hearing status in 2006 and had no SCF concerns in 2008. To assess SCF, researchers administered questionnaires in 2008, 2012, and 2016 that included six yes/no questions.

Not surprisingly, men who reported greater hearing loss were more likely to be older, the researchers note. However, there were no other large differences between this group and others.

During the study's 52,752 person-years of follow-up, investigators found 2771 cases of incident SCF decline, defined as an SCF score of 1 or more.

Compared to men with no hearing loss, the multivariable-adjusted relative risk of incident cognitive decline was 1.30 (95% confidence interval [CI], 1.18 - 1.42) for mild hearing loss, 1.42 (95% CI, 1.26 - 1.61) for moderate hearing loss, and 1.54 (95% CI, 1.22 - 1.96) for severe hearing loss with no use of hearing aid (P-trend < .001).

Small Difference with Hearing Aids

Among the 623 participants with severe hearing loss who used hearing aids, the magnitude of the elevated risk was somewhat attenuated at 1.37 (95% CI, 1.18 - 1.60). However, this risk was not statistically significantly different from the risk among the 196 men with severe hearing loss who did not use hearing aids (P = .4).

The researchers note that this may be due to limited power or may suggest that if a difference does exist, the magnitude of the effect may be modest.

Among participants who did not use hearing aids, increasing severity of hearing loss tended to be associated with a higher risk of cognitive decline (P-trend < .001).

The relation between hearing loss and cognitive decline did not vary by age (P-interaction = .9) or by depression (P-interaction = .5).

When investigators compared poor vs good SCF, the multivariable-adjusted odds ratio was 2.07 (95% CI, 1.76 - 2.43) for mild hearing loss; 2.49 (95% CI, 2.04 - 3.04) for moderate hearing loss; and 4.92 (95% CI, 3.61 - 6.71) for severe hearing loss with no use of hearing aid. The likelihood for each of these groups was compared to those with no hearing loss.

Among men with severe hearing loss who used hearing aids, the multivariable-adjusted odds ratio for poor vs good SCF was 2.92 (95% CI, 2.37 - 3.60).

"Health care providers should be aware that individuals with hearing loss may be at higher risk for cognitive decline," Curhan said. "Managing hearing loss with lifestyle and environmental adaptations, hearing rehabilitation, and hearing aids could possibly be an early stage intervention that could help prevent or slow the progression of cognitive decline."

When the researchers performed a sensitivity analysis that included questions about SCF that were not potentially influenced by hearing status, the size of the associations were somewhat reduced.

"This suggests that some measures typically used in cognitive testing could be sensitive to hearing ability," Curhan said.

"This can be a challenge and underscores an important message from this study: Clinicians should be aware that hearing loss could potentially influence performance on certain cognitive measures, so hearing ability should be taken into account when conducting a cognitive assessment."

Cognitive assessments that do not rely on auditory ability may be preferable, she added.

Important Research Implications

Another implication, this time for researchers, is that hearing status could be an important methodologic consideration in studies of cognitive decline and dementia.

Although several plausible mechanisms could explain an association between hearing loss and cognitive decline, "the underlying pathophysiology remains unclear," the researchers note.

Hearing loss may make listening more effortful and understanding speech more difficult, thereby increasing cognitive load and requiring the recruitment of additional cognitive resources, Curhan said.

As a result, over time, chronic compensation could result in changes in neural networks, altered allocation of cognitive resources, and depletion of cognitive resources.

In addition, there could be shared mechanisms that contribute to both auditory and cognitive decline, and these contributions may accumulate over time with advancing age. For example, vascular, oxidative, and inflammatory processes — as well as genetics — may play a role, and the effects could accumulate over time with advancing age, she added.

Furthermore, hearing loss may encumber social relationships and hamper social engagement, leading to social isolation and depression that may increase risk of cognitive decline.

There is growing evidence that lifestyle factors may influence dementia risk. It has been suggested that more than one third of dementia cases may be preventable with lifestyle change and effective management of personal habits (eg, maintaining social engagement, smoking cessation) and medical conditions (such as depression, diabetes, hypertension, and obesity).

"Possibly, more effective management of hearing loss, or even preventing hearing loss, could [also] contribute to the prevention or delay of dementia," said Curhan.

Future research plans for Curhan and her team include investigating relationships between self-reported hearing loss, change in audiometric hearing thresholds, and changes in cognition using a number of different assessment measures.

They also plan to investigate the association between changes in measured audiometric hearing thresholds and cognition among participants in the Conservation of Hearing Study (CHEARS) Audiometry Assessment Arm, a sub-study conducted in 3749 female participants in the longitudinal Nurses' Health Study II.

Shared Mechanisms?

Commenting on the findings for Medscape Medical News, Pinky Agarwal, MD, FAAN, a movement disorders neurologist at the Booth Gardner Parkinson's Care Center and clinical professor at the University of Washington School of Medicine in Kirkland, Washington, described the study as "well-conducted."

The research showed that "more severe hearing loss is associated with higher risk of complaints of memory problems, which has been reported to correlate with risk of dementia. Increased emphasis should be placed on trying reversible causes of hearing loss as a means to protect memory," said Agarwal, who was not involved with the research.

Agarwal said that the generalizability of results beyond well-educated, white males working in the health profession likely is limited.

In addition, she proposed that wearing hearing aids helped but not to a significant degree "since underlying mechanisms causing hearing loss may be the same as those causing cognitive worsening."

Curhan and Agarwal have disclosed no relevant financial relationships. The study was supported by multiple NIH grants.

Alzheimer's & Dementia. Published online January 29, 2019. Full text

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