July 2020 The Hearing Journal
Hearing loss is the third most common chronic disease affecting older adults and is associated with poorer physical health, depression, loneliness, and isolation. Despite these detrimental effects on quality of life and financial cost to society, hearing loss remains significantly undertreated, with reports of only 11 percent of older adults with hearing loss owning hearing aids and around 24 percent of this group not using them.
Hearing loss is associated with a greater rate of cognitive decline in older adults and was acknowledged by The Lancet Commission's expert group on dementia to be a modifiable risk factor for the disease. While most studies on cognitive decline focus on older adults, recent data indicate that hearing loss onset in mid-life is associated with a dementia diagnosis before 60 years of age (i.e., early-onset dementia). Thus, in both mid- and later life, hearing loss increases the risk for cognitive decline and dementia.
Given the risk of hearing loss for cognitive decline and the acknowledgment that this could be a modifiable risk factor for dementia, researchers have sought to determine whether remediation of hearing loss with hearing aids could influence cognition. Unfortunately, these investigations provide little clear evidence on the benefits of hearing aid use, most likely due to limitations in the study designs such as small sample sizes, insensitive screening, cognitive tests that require good auditory acuity, failure to objectively assess hearing loss and device effectiveness, and failure to measure and control for other dementia risk factors. In this longitudinal cohort study of older adults with hearing loss in Australia, we aimed to address these limitations and compare the cognitive outcomes of first-time hearing aid users before and 18 months after hearing aid fitting.
Cognition was measured over time in a prospectively recruited cohort of 99 older adults (53 women) with hearing loss aged 62-82 years. Of these, 71 percent were retired and 67 percent were tertiary educated, making it a highly educated sample. Cognitive assessments were conducted using the Cogstate Cognitive Battery, which measures psychomotor function, attention, working memory, visual learning, and executive function. This test battery is a highly reliable computerised tool that uses visual instructions only. Audiological hearing assessments using standard audiometric procedures were conducted in a sound-treated room by an audiologist before and 18 months after hearing aid fitting. Mean pure-tone average (PTA) in the better ear was 31 dB HL, with no significant difference in hearing loss between the men and women. The NAL-NL2 prescription was used for most participants, and the prescription gain was verified using real-ear measures (insertion gain). The amount of hearing aid use was measured using data logging and questionnaires, and objective and subjective benefits of use (speech perception and ease of listening) were measured using consonant-vowel-consonant (CVC) words, speech reception threshold testing, and the Abbreviated Profile of Hearing Aid Benefit. Data for other known risk factors for cognitive decline, including physical health, mood, social isolation, loneliness, physical activity, quality of life, and sex, were also collected and included in multiple linear regression analyses. Data collection in a comparison group of older Australians with typical hearing for their age is also ongoing. When this yields a sample size large enough for comparison, cognitive and other outcomes will be compared between the two groups.
BEFORE HEARING AID USE
Prior to hearing aid fitting, no significant difference in hearing loss was found between the men and women, and the level of hearing loss was not associated with age. Mood and anxiety levels were within normal limits, with only 17 percent of participants reporting elevated anxiety symptoms and four percent reporting elevated depressive symptoms. The low number of people with anxiety and/or depression may be partly because on average, the participants’ degree of hearing loss was only mild to moderate, and therefore the impact of hearing loss on mental health and loneliness was not severe. Higher educational attainment has also been shown to have a protective effect against depression and anxiety. However, 44 percent of the participants reported feeling lonely. The mean Health Utilities Index mark 3 (HUI3) overall quality of life score was 0.74 (which is quite high relative to the maximum score of 1). Multiple linear regression analysis showed that at baseline, the level of hearing loss and age predicted poorer executive function, while increasing educational attainment was related to better executive function and visual learning.
OUTCOMES AFTER 18 MONTHS
Cognition was re-assessed in 37 participants (20 men, 17 women) 18 months after hearing aid fitting. Twenty-eight percent were using their hearing aids more than 90 percent of waking hours, and 31 percent used their device in 60-90 percent of waking hours. Speech perception in quiet and quality of life across the group significantly improved, while 57 percent of self-reported listening disability scores had improved significantly. Participants with elevated anxiety and depressive symptoms at baseline did not report either of these conditions at 18 months. Likewise, the participants who were severely lonely at baseline were not at 18 months, although one participant was severely lonely at 18 months but not at baseline.
Group mean performance improved for the measure of executive function and that on the measures of psychomotor function, attention, working memory, and visual learning did not decline across 18 months. Reliable Change Index scores, which indicate whether a clinically significant change has occurred, also showed either significant improvement or stability in executive function for 97 percent of participants (Fig. 1).
Figure 1: Individual trajectories of executive function from baseline to 18 months post-hearing aid fitting (N = 37). Blue lines: improvement (decreased score); red lines: decline (increased score); solid lines: clinically significant change; dotted lines: non-significant change.
At follow-up, 30 percent of follow-up participants had improved on executive function, 67 percent remained stable, and only three percent had declined. Clinically significant improvement was also observed in the working memory, visual attention, and visual learning of female participants.
Upon exploring cognitive changes in terms of hearing aid use, significantly greater gains in executive function were found in participants who used their devices for more than 90 percent of waking hours compared with those who used their devices for less than 90 percent of waking hours. Women participants used their hearing aids more regularly and for longer periods than did men (56% v. 33% in a 14-hour day). Greater gains in executive function, along with significant improvements in three other Cogstate subtests among the female participants, suggest a dose-effect of hearing aid use on cognition. Previous studies have reported this difference in the pattern of hearing aid use between men and women, suggesting that it may be because women value social communication more than men, have a greater awareness of the problems hearing loss causes, and experience greater levels of stress and anger related to hearing loss.
Given the high average education levels in this study cohort and the likely higher cognitive reserve in this group compared with the general population, these results are likely not representative of the general population. However, while a slower rate of cognitive decline may well be expected in such a well-educated cohort, the improvements in cognition observed in this study would not be expected in older adults. The observed improvement, along with the lack of decline, was not expected after such a short follow-up period. Further follow-up of a larger sample in the future will allow outcomes across a greater range of education levels to be examined.
This study addressed many of the limitations of past research by objectively measuring hearing loss, treatment effects, and compliance; using a visually presented cognitive assessment tool; and controlling for other risk factors for cognitive decline. High levels of stability, as well as clinically and statistically significant group improvement in executive function, were observed after 18 months of hearing aid use. Our initial results suggested that the treatment of hearing loss with hearing aids may delay cognitive decline. These encouraging results indicate that hearing aid use could be a safe and comparatively economical method of preserving the cognitive function and quality of life of older adults for longer, thereby also reducing caregiver burden and facilitating significant aged care cost savings for the community. To confirm these results, a longer follow-up period and larger sample size are needed. An investigation into the observed differences in benefit and treatment compliance between men and women may also be useful in terms of developing appropriate clinical management programs.