20Q: Hearing Loss and Its Comorbidities

From the Desk of Gus Mueller

As audiologists, we’re pretty good at understanding co-existing auditory pathologies. We’ve all seen the patient with a noise induced hearing loss who also has middle ear effusion. And, on occasion there is the presumed cochlear dysfunction in the presence of a nVIII space occupying lesion. And commonly, there is the elderly person with a mild sensorineural impairment, who also has central auditory processing deficits. All of this relates to dysfunction within the auditory system, but there often are other related disorders that we don’t think about as often, commonly referred to as comorbidity.

Comorbidity is an important topic for audiologists to consider.  There are some diseases and disorders that are more likely than others to be comorbid with one another. For example, most of us are aware of the relationship between diabetes and retinopathy. But what about the relationship between diabetes and hearing loss? Or, the relationship between hearing loss and depression, cognition, cerebrovascular and cardiovascular disorders, falls, and the list goes on. Knowledge of all these relationships is important for effective patient care and counseling, and for communication with other medical professionals.

Definitive research linking hearing loss to many other diseases and disorders has only emerged in the last decade or so.  To bring us up to date in this important area, we have brought in an expert on the topic, Harvey Abrams, PhD.  Dr. Abrams serves as a Senior Research Consultant to Starkey Hearing Technologies.  He also consults for the Hearing Industries Association and the Better Hearing Institute. You’ll also want to check out Harvey’s monthly column at Hearing Health and Technology Matters titled “Peeling the Onion,” where he offers insightful comments regarding recent audiologic happenings.

Some of you know Dr. Abrams from his many years with the Department of Veterans Affairs, and his long list of publications on outcome measures, health-related quality of life, and treatment efficacy. His extensive background in research and hearing health care management provide an excellent background for him to help us understand the world of hearing loss comorbidities.

Gus Mueller, PhD
Contributing Editor
September 2017

Browse the complete collection of 20Q with Gus Mueller CEU articles at www.audiologyonline.com/20Q

20Q: Hearing Loss and Its Comorbidities

    Harvey Abrams

1. It seems that every time I look at the literature, another disorder is being linked with hearing loss. What’s going on here?

Yes, you’re right. I think the increase in studying comorbidities in general and the number of reported studies linking hearing loss to other chronic diseases, in particular, are the result of several converging factors. These factors include: society’s increased focus on wellness; an aging population; a growing appreciation for the importance of healthy hearing as a marker of healthy aging; the increasing prevalence of hearing loss in this country; the availability of “big data”; and, an increased sophistication in epidemiological data analysis.

2. I want to discuss these factors in more detail, but first - what exactly is meant by “comorbidity”?

Right. So, let’s define some of these terms. First of all, when we speak of comorbidity, we’re generally referring to the co-existence of two or more chronic conditions in a single patient. When we say chronic, we’re referring to a disease that lasts for more than three months.

3. That seems pretty reasonable, but is hearing loss really a chronic condition?

I would argue that it is. If you compare it to diabetes, for example, they share many similar characteristics. For example, hearing loss and diabetes are both invisible, progressive, painless, long-lasting, and often incurable but treatable. Most importantly, when the patient takes responsibility for self-managing diabetes or hearing loss, the outcomes are usually positive. In fact, if we can change our current view of hearing loss as an acute condition that can be fixed through the use of a device, and instead understand the chronic nature of the disorder and its psychosocial consequences, we’d probably be having a different conversation about over-the-counter (OTC) devices these days.

4. You've convinced me that hearing loss is a chronic condition. You mentioned that one of the reasons for an increase in comorbidity studies is the increased use of epidemiological data. Could you expand on this?

Of course.  Epidemiology is the study of the nature and occurrence of disease in different populations. In clinical research, we look at the effect of a specific intervention on an outcome related to a specific disease among a carefully selected sample of the population.  However, epidemiological research is not interventional; it attempts to determine the causes (risk factors) associated with a disease by looking at characteristics of the population and the disease (or diseases) of interest. For example, we may be interested in determining the occurrence of hearing loss among all entering freshmen at a state university. In addition to testing hearing, we would ask the freshmen questions about their general health, recreational activities, family health history, etc. The analysis of the data would seek to determine if there were relationships between the existence of hearing loss and any of those other factors we queried. If we asked the right questions, we might find out that those whose thresholds exceeded normal levels were more likely to engage in activities that exposed them to high levels of noise, had family members with hearing loss, or suffered multiple bouts of ear infections as a child. The data could also determine the relative strength of each of those associations.

5. So, in this example you would look to see if the differences in the occurrence of hearing loss are statistically different between those students exposed to noise, for example, and those who are not?

Not quite. Unlike clinical research where you are looking for statistically defined differences between, let’s say, a treatment group and a placebo group, in epidemiological research the researchers are measuring the strength of associations between a disease and specific features of the population. These associations are often expressed as the “odds” of a disorder occurring or the “risk” of an individual experiencing the disease of disorder given a particular characteristic that exists in the population.

6. “Odds” and “risks?” Sounds more like poker and investment strategies than health care concepts.

Maybe so, but some definitions will be helpful. Here’s some terminology that is common in large population or epidemiological studies:

• Odds ratio (OR) refers to the odds that an outcome (e.g. falling) will occur given a particular exposure (e.g. hearing loss), compared to the odds of that outcome occurring in the absence of that exposure. For example, let’s say that the data in study X revealed that the odds of falling were twice (OR = 2.0) as likely among those with hearing loss than those without hearing loss. This is not to say that those without hearing loss don’t fall but that the odds of a person without hearing loss falling is less than that of a person with hearing loss.
• Risk ratio (RR) (sometimes referred to as relative risk) is defined as the cumulative risk of an outcome occurring over a time span. For example, study Y reveals that, after following a specific population that was dementia-free at the beginning of data collection, the cumulative risk of being diagnosed with dementia after 15 years was 2.2 times greater (RR = 2.2) among those who did not wear hearing aids than those who did.
• Hazard ratio (HR) is similar to risk ratio but describes the risk of a disorder being diagnosed at a particular point in time (not cumulative). For example, study Z reveals that the risk of having hearing loss is 1.5 times greater at 5 years post-baseline among those diagnosed with CVD than those without a CVD diagnosis (HR = 1.5).

7. I’ve sometimes seen the term “adjusted” used to describe an odds or hazards ratio. What does that mean?

This is an important concept. In the context of reporting epidemiologic data, “adjusted” means that the data have taken into account other confounding variables that might be responsible for the effect.  For example, say we were looking at hearing loss and frequency of falls.  We know that older people tend to have hearing loss. If we find that people with hearing loss tend to fall more than those with normal hearing, couldn’t falls simply be an effect of aging and have nothing to do with hearing loss? Biostatisticians (bless their hearts) employ specific statistical treatments to, for example, remove age as a factor in the analysis so that hearing loss can be examined as an independent risk factor associated with the outcome of interest – in this case, falls.

8. Well, thank you for helping me get up to speed on epidemiological studies. What do these studies tell us about the relationship between hearing loss and other chronic conditions?

The research has been fairly compelling in terms of establishing a relationship between hearing loss and other disorders such as: social isolation and loneliness, depression, falls (which is not really a comorbid condition, but rather an event), cardiovascular disease, diabetes, and dementia. There are additional conditions that are emerging as possible comorbidities including fibromyalgia, anemia, rheumatoid arthritis, kidney disease, and sleep apnea.

9. You mentioned a link between hearing loss and dementia.  We’ve all seen a lot of articles in the popular press describing that relationship. Your thoughts?

This particular association has gotten a lot of attention in both the professional and consumer communities.  There’s considerable concern that, as our population ages, we will encounter a growing number of our patients suffering cognitive decline, Alzheimer’s disease, and other forms of dementia. Separate from our professional interest, we’re concerned about our own family members and, indeed, ourselves. Perhaps, the landmark study on this relationship was conducted by Frank Lin and colleagues and published in 2011 (Lin et al., 2011). The researchers prospectively studied 639 participants in the Baltimore Longitudinal Study of Aging project who were dementia free in 1990-1994 and followed them for a median period of just under 12 years. During this time, 58 cases of incident all-cause dementia were diagnosed, of which 37 cases were diagnosed as Alzheimer’s disease. The authors found that the risk of incident all-cause dementia as well as Alzheimer’s disease increased with the severity of baseline hearing loss. After adjusting for other contributing factors (recall I described the technique of adjusting earlier), the results suggested that hearing loss was independently associated with incident all-cause dementia and that the risk increased as a function of the degree of hearing loss. Specifically, the hazard ratio (HR) was 1.89 for mild hearing loss; 3.0 for moderate hearing loss; and 4.94 for severe hearing loss. In terms of Alzheimer’s disease specifically, the risk also increased with baseline hearing loss, the HR equaling 1.20 per every additional 10 dB of hearing loss.

10. Are there more recent studies that support a relationship between hearing loss and dementia?

Indeed, there are. One such example is a large longitudinal epidemiological study conducted by Fritze and colleagues (2016) that examined claims data from a cohort of 154,783 persons aged 65 and older from Germany’s largest health insurer (epidemiological studies often involve very large data sets). The claimants’ health status was followed between the years of 2006 and 2010 during which time 14,602 incident dementia diagnoses were made. Gender, age, and comorbidities were controlled for (i.e., adjusted) as potential confounders. It turned out, consistent with Lin et al (2011), that patients with bilateral hearing impairment had higher risks of dementia incidence than patients without hearing impairment and that the cumulative incidence of dementia increased each year from 2006 through 2010.

11. The evidence linking hearing loss and dementia is, indeed, compelling, right?

Yes, but remember that association does not imply causation.  We have to be very cautious that, as clinicians, we don’t make that assumption or make such claims to our patients. To do so would be irresponsible, at best. For an excellent review of the issues associated with the link between hearing loss and dementia, I suggest another 20Q article that featured Dr. Piers Dawes who has conducted his own research in this area (Dawes, 2017). However, I would like to suggest an intriguing possible explanation for this association. In a recent study published in JAMA Psychiatry, Nancy Donovan and colleagues (2016) examined the relationship between loneliness and cortical amyloid burden in cognitively normal older adults. Studies have shown that there is a link between the presence of amyloid plaques in the brain and dementia of the Alzheimer's type (i.e., Alzheimer’s disease). The researchers found that, after controlling for a number of other factors, higher amyloid burden was significantly associated with loneliness as measured by the UCLA Loneliness Scale. Those in the amyloid positive group were 7.5 times more likely to be classified as lonely than non-lonely.

12. That is intriguing but how do we get from hearing loss to dementia?

Here’s how: There’s emerging evidence linking hearing loss to loneliness. As an example, Sung and colleagues (2016) examined factors associated with loneliness in a group of 145 participants enrolled in the SMART study (Studying Multiple Outcomes after Aural Rehabilitation) between the years 2011- 2013.  Loneliness was measured using the UCLA Loneliness Scale. The researchers found that younger age and greater hearing loss were significantly associated with greater loneliness. If hearing loss is associated with loneliness, and loneliness is associated with increased cortical amyloid burden, and increased amyloid burden is associated with Alzheimer’s disease, perhaps we have one possible mechanism to explain the association between hearing loss and dementia.

13. Dementia, Alzheimer’s disease, loneliness – I’m beginning to feel depressed.

As it turns out, if you have hearing loss you may have reason to be concerned about depression. Mener and colleagues (2013) examined data from the 2005–06 and 2009–10, 2-year cycles of the National Health and Nutrition Examination Survey (NHANES), involving 1,029 individuals 70 years of age and older. Depression was measured by the PHQ-9 (Patient Health Questionnaire), a self-assessment measure. The results indicated that the odds of self-reporting a major depressive disorder increased 1.5 per 25 dB PTA in the better ear. The odds of self-reporting any depressive symptom increases to 1.63 per 25 dB.  The results suggested that hearing loss was independently associated with depression. Similar findings were reported in a 12-year (2000 – 2011) review of the Taiwan National Insurance Research Database which included 5,043 patients with SNHL and 20,172 without (Hsu et al, 2016). The analysis revealed that the risk of depression was higher in the hearing loss cohort, the hazard ratio being 1.73, again suggesting that hearing loss is an independent risk factor associated with depression. Just to add one more study to the evidence, Li and colleagues (2014) examined data from 18,318 individuals who participated in the NHANES from 2005-2010.  The researchers were particularly interested in examining depression as a function of the severity of hearing loss and there appears to be a direct relationship between the two with the odds ratio for moderate to severe depression increasing as self-reported hearing progresses from “good” to “a lot of trouble”.

14. What do we know about the association between hearing loss and falls?  I may need to brush up on my vestibular assessment skills.

Lin and Ferrucci (2012) examined the association between falls and hearing loss among 2,017 NAHNES participants from 2001 to 2004 and found a significant association between the two with 1.4-fold increased odds of reporting a fall in the previous 12 months for every 10 dB of hearing loss. As many of our readers know, falls are a leading cause of fatal and non-fatal injuries among the elderly and are associated with significant health, social, economic, and emotional consequences.

15. I can understand the relationship between hearing loss and some of the comorbidities you mentioned like depression. But diabetes - is that really linked to hearing loss?

The evidence supporting an association between the two appears to be strong. Horikawa and colleagues (2013) performed a systematic review and meta-analysis of the literature in an attempt to determine the prevalence of hearing impairment among diabetic and non-diabetic adults.  For those unfamiliar with meta-analyses, it is a statistical technique that can often reveal meaningful effects by combining the data among several studies that are obscured in individual studies – particularly those with small sample sizes. This systematic review analyzed the data from 13 eligible studies involving 20,194 participants and 7,377 cases. The meta-analysis revealed that the prevalence of hearing loss among those with diabetes was more than twice that of those without diabetes. The association between hearing loss and diabetes was stronger in those younger than 60 years of age but was independent of gender or chronic exposure to noise. Consistent with these findings, Bainbridge and colleagues (2008) examined the association between hearing loss and diabetes among 5,140 participants in the NHANES from 1999-2004 and found that people with diabetes had statistically significant increased odds of hearing impairment in worse and better ears at all levels of severity and frequency. The association between diabetes and hearing impairment was independent of known risk factors for hearing impairment, such as noise exposure, ototoxic medication use, and smoking. In a prospective cohort study (Kim et al, 2016), over 253,000 adults with baseline normal hearing were followed from 2002 to 2014. Among this large cohort, the hazard ratio for developing hearing loss, adjusted for noise exposure, BMI, smoking, alcohol use, and exercise, was 1.04 among those with pre-diabetes and 1.4 for those with diabetes.

16. What might explain the association between hearing loss and diabetes?

One explanation that has been posited is that, overtime, high blood glucose levels damages the blood vessels in the cochlea and specifically the stria vascularis, impacting the neural innervation and biochemistry of the cochlea – certainly one of the many good reasons for individuals to properly manage their diabetes and, if at all possible, to reduce the risks of its occurrence in the first place through proper diet and exercise.

17. Can hearing aids help to limit the consequences of hearing loss for some of the conditions we’ve discussed? 

Yes, that’s the good news. In terms of falls, for example, Rumalla and colleagues (2014) demonstrated that participants were able to maintain postural stability for a longer period of time as measured by the Romberg and tandem tests, following 30 days of hearing aid use.  A number of recent studies have shown the positive effects of hearing aids on depression. For example, in the NANHES study I described earlier, Mener et al (2013) showed a significantly lower odds ratio of reporting a major depressive disorder among those who reported wearing hearing aids (OR = .28) as compared to those who did not report wearing hearing aids (OR = 1.50). As you can imagine, there’s been considerable interest in the effects of hearing aids on cognition, and specifically on reducing the onset or severity of dementia. Piers Dawes and colleagues (2015) found that hearing aid use had a positive effect on cognition which was independent of social isolation and depression among a subsample of 164,770 adults in the UK Biobank data set. In a prospective study of the effects of hearing aids on psychosocial and cognitive status, Acar and colleagues (2010) were able to demonstrate a significant improvement in cognitive performance after 3 months of hearing aid use as measured by the Mini Mental Status Examination. It’s also useful to look at the most recent MarkeTrak and EuroTrak data which also support the benefits of amplification on depression and forgetfulness, for example (Hougaard, Ruf, Egger, & Abrams, 2016).

18. Is the evidence strong enough to advise our patients that hearing aids can reduce the onset or severity of dementia?

I’m afraid not. Just as the comorbidity evidence is mostly correlative, so is the evidence for the benefits of amplification. Much of that evidence is population-based, and what prospective research that does exist is based on small samples or non-randomized controlled clinical trial data. Fortunately, there are two very large and ambitious randomized trials underway that may add significantly to our understanding of the relationship between hearing loss and cognition and the role that audiologic intervention plays in mitigating the consequences of hearing loss.  One large scale study called the ACHIEVE study (Aging Cognition and Hearing Intervention & Evaluation in Elders) is in the works is headed by Frank Lin. This research is funded by the National Institute of Aging. Its aims are to determine the effects of best-practices hearing rehabilitative treatment on rates of cognitive decline in 70-84 year-old well-functioning and cognitively-normal older adults with hearing loss and to investigate the mechanistic pathways through which hearing rehabilitative treatment affects cognitive functioning. The second study, with which I’m associated, is labeled SENSE-Cog. Piers Dawes is the Co-Principal Investigator of this 5-year project that is funded by the European Union’s Horizon 2020 Research and Innovation Program and involves seven nations across Europe. Among its many aims are: to gain a better understanding of the links among hearing, vision, cognitive and emotional systems; to develop new tools and at-home support that could improve quality of life; and, to help optimize health and social care budgets and resource allocation across Europe.

19. What does this all mean for my day-to-day practice?

I think information on comorbidities can inform daily practice in a number of important ways. For example, if we haven’t yet done it, we should update our history forms to identify those conditions that may co-exist with hearing loss such as diabetes, falls, depression, and cognitive disorders. We need to screen for cognitive dysfunction and depression, particularly among our older patients.  We also need to develop, build and strengthen our relationships with other healthcare professionals such as primary care physicians, psychologists and neuropsychologists in order to make timely and appropriate referrals when screening suggests a need to do so. It has become abundantly clear that age-related hearing loss is not a simple nor a benign consequence of aging and it must no longer be treated so cavalierly by the general healthcare community. It’s incumbent upon all of us in the hearing care professions to communicate the potentially serious consequences of hearing loss and the mitigating influence of audiologic intervention to our allied health colleagues whenever possible.

20. I suspect you’ve just scratched the surface of this complex topic. Where can I find additional information?

I recently presented a webinar on this topic that goes into more detail on the studies I cited - you can access it on the Hearing Review website. In addition, I would also suggest reading at least a few of the articles in the reference list to get an appreciation for the scope of issue and the benefits of epidemiological research for uncovering many of the associations I reviewed in this discussion. For those interested specifically in issues associated with dementia prevention, intervention, and management, I would suggest an outstanding, recently published review article by Livingston and colleagues (2017). The article pays considerable attention to hearing loss as a modifiable risk factor for dementia.

References

Abrams, H.B., & Kihm, J. (2015). An introduction to MarkeTrak IX: A new baseline for the hearing aid market. Hearing Review, 22(6), 16-22. 

Acar, B., Yurekli, M.F., Babademez, M.A., Karabulut, H., & Karasen, R.M. (2011). Effects of hearing aids on cognitive functions and depressive signs in elderly people. Arch Gerontol Geriatr., 52(3), 250-2. doi: 10.1016/j.archger.2010.04.013

Bainbridge, K.E., Hoffman, H.J., & Cowie, C.C. (2008). Diabetes and hearing impairment in the United States: Audiometric evidence from the National Health and Nutrition Examination Survey, 1999-2004. Ann Intern Med., 149(1), 1-10.

Dawes, P., Emsley, R., Cruickshanks, K.J., Moore, D.R., Fortnum, H., Edmondson-Jones, M.,...Munro, K.J. (2015). Hearing loss and cognition: the role of hearing aids, social isolation and depression. PLoS One, 10(3), e0119616. doi: 10.1371/journal.pone.0119616

Donovan, N.J., Okereke, O.I., Vannini, P., Amariglio, R.E., Rentz, D.M., Marshall, G.A.,...Sperling, R.A. (2016). Association of higher cortical amyloid burden with loneliness in cognitively normal older adults. JAMA Psychiatry, 73(12), 1230-1237. doi: 10.1001/jamapsychiatry.2016.2657

Fritze, T., Teipel, S., Óvári, A., Kilimann, I., Witt, G., & Doblhammer, G. (2016). Hearing impairment affects dementia incidence. An analysis based on longitudinal health claims data in Germany. PLoS ONE, 11(7), e0156876. doi:10.1371/journal.pone.0156876

Horikawa, C., Kodama, S., Tanaka, S., Fujihara, K., Hirasawa, R., Yachi, Y.,...Sone H. (2013). Diabetes and risk of hearing impairment in adults: a meta- analysis. J Clin Endocrinol Metab., 98(1), 51-8. doi: 10.1210/jc.2012-2119

Hougaard, S., Ruf, S., Egger, C., & Abrams, H. (2016). Hearing aids improve hearing–and A LOT more. Hearing Review, 23(6),14.

Hsu, W.T., Hsu, C.C., Wen, M.H., Lin, H.C., Tsai, H.T., Su, P.,...Hsu, Y.C. (2016). Increased risk of depression in patients with acquired sensory hearing loss: A 12-year follow-up study. Medicine (Baltimore), 95(44), e5312.

Kim, M.B., Zhang, Y., Chang, Y., Ryu, S., Choi, Y., Kwon, M.J.,...Cho J. (2016). Diabetes mellitus and the incidence of hearing loss: A cohort study. Int J Epidemiol., pii: dyw243. doi: 10.1093/ije/dyw243

​Li, C.M., Zhang, X., Hoffman, H.J., Cotch, M.F., Themann, C.L., & Wilson, M.R. (2014). Hearing impairment associated with depression in US adults, National Health and Nutrition Examination Survey 2005-2010. JAMA Otolaryngol Head Neck Surg., 140(4), 293-302. doi: 10.1001/jamaoto.2014.42

Lin, F.R., Metter, E.J., O’Brien, R.J., Resnick, S.M., Zonderman, A.B., & Ferrucci, L. (2011). Hearing loss and incident dementia. Arch Neurol., 68(2), 214-20. doi: 10.1001/ archneurol.2010.362

Lin, F.R., & Ferrucci, L. (2012). Hearing loss and falls among older adults in the United States. Arch Intern Med., 172(4), 369-371.

Livingston, G., Sommerland, A., Orgeta, V., Costafreda, S.G., Huntley, J., Ames, D.,...Mukadam, N. (2017). Dementia prevention, intervention, and care. Lancet Commissions. pii: S0140-6736(17)31363-6. doi: 10.1016/S0140-6736(17)31363-6

Mener, D.J., Betz, J., Genther, D.J., Chen, D., & Lin, F.R. (2013). Hearing loss and depression in older adults. J Am Geriatr Soc., 61(9), 1627-1629. 

Rumalla, K., Karim, A.M., & Hullar, T.E. (2015). The effect of hearing aids on postural stability. Laryngoscope, 125(3), 720-3. doi: 10.1002/lary.24974

Sung, Y.K., Li, L., Blake, C., Betz, J., & Lin, F.R. (2015). Association of hearing loss and loneliness in older adults. J Aging Health, 28(6), 979-994.