International Journal of Audiology 2014; 53: 392–401

Original Article

Comorbidity in adults with hearing difficulties: Which chronic medical conditions are related to hearing impairment?

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Mariska Stam*, Piet J. Kostense†, Ulrike Lemke‡, Paul Merkus*, Jan H. Smit#, Joost M. Festen* & Sophia E. Kramer* *Department of Otolaryngology-Head and Neck Surgery, section Audiology, VU University Medical Center and EMGO Institute for Health and Care Research, Amsterdam, The Netherlands, †Department of Epidemiology and Biostatistics, VU University Medical Center and EMGO Institute for Health and Care Research, Amsterdam, The Netherlands, ‡Phonak AG, Science and Technology, Stäfa, Switzerland, and #Department of Psychiatry, VU University Medical Center/GGZ in Geest and EMGO Institute for Health and Care Research, Amsterdam, The Netherlands

Abstract Objectives: To investigate the occurrence of 27 chronic medical conditions in a cohort of adults with and without hearing impairment, and to examine the association between these conditions and hearing ability. Design: The National Longitudinal Study on Hearing (NL-SH study) is a large prospective study among adults aged 18 to 70 years, conducted via the internet in the Netherlands. Hearing ability was measured with a digits-in-noise test and comorbidity was assessed through self-report. Study sample: Cross-sectional data of 890 hearing-impaired and 975 normally-hearing adults were analyzed. Both descriptive statistics and multinomial logistic regression analyses were conducted. Results: Of the NL-SH participants with insufficient or poor hearing ability, 78.5% reported to suffer from at least one additional chronic condition. This proportion was larger than in the normally-hearing group (68.6% with one or more chronic conditions and 37.7% with two or more). After adjustment for age and gender, ‘dizziness causing falling’, ‘diabetes’ and ‘arthritis types other than osteoarthritis and rheumatic arthritis’ were significantly associated with poor hearing ability. Conclusions: Our results show that some previously reported associations do not only occur in older age groups, but also in younger cohorts. Comorbidity is relevant in the rehabilitation (multi-disciplinary care) and the clinical encounter.

Key Words: Comorbidity; hearing problems; epidemiology; adults; diabetes

It is known that adults with hearing impairment often also suffer from other health problems concurrent with their hearing loss, especially with increasing age (Kramer et al, 2002). The co-existence of two or more chronic health conditions in an individual can be described by the term ‘comorbidity’. It is “the existence or occurrence of any distinct additional entity during the clinical course of a patient who has the index disease under study” (Feinstein, 1970). It becomes more prevalent with age as aging affects the function of all organ systems and old age is often associated with longer lasting convalescence and more chronic medical conditions (SteinhagenThiessen & Borchelt, 1999). When regarding hearing impairment, literature shows that there is an obvious co-existence of hearing loss with ear, nose, and throat (ENT) symptoms, such as tinnitus, dizziness, and balance problems (Davis et al, 2007). Also the co-existence of hearing problems with diabetes mellitus (further referred to as diabetes)

has been reported. Examples of large representative cohort studies showing such a relationship are: Crews & Campbell, 2004; Helzner et al, 2005; Bainbridge et al, 2008; Agrawal et al, 2009; Maggi et al, 1998. However, in their recent study among 717 older Americans (⬎ 70 years of age), Lin and colleagues did not observe pure-tone hearing loss coexisting with diabetes (Lin et al, 2011). The same inconsistency in results applies to the coexistence of hearing impairment and cardiovascular diseases. Several studies found a relationship between cardiovascular health and the function of the auditory system (Cruickshanks et al, 1998; Gates et al, 1993). However, other studies reported the absence of such a relationship (Lin et al, 2011; Helzner et al, 2011). It seems apparent that more knowledge is required to add to the evidence whether or not hearing impairment is related to diabetes or cardiovascular diseases. In addition, little attention has

Correspondence: Mariska Stam, Department of Otolaryngology-Head and Neck Surgery, section Audiology, VU University Medical Center and EMGO Institute for Health and Care Research, P.O. Box 7057, 1007 MB Amsterdam, The Netherlands. E-mail: [email protected] (Received 12 July 2013; accepted 20 December 2013) ISSN 1499-2027 print/ISSN 1708-8186 online © 2014 British Society of Audiology, International Society of Audiology, and Nordic Audiological Society DOI: 10.3109/14992027.2013.879340

Comorbidity in adults with hearing impairment

Abbreviations

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NL-SH OR SRTn

National Longitudinal Study on Hearing Odds ratio Speech-Reception-Threshold in noise

been paid so far to comorbidity of other (less obvious or less prevalent) diseases that might co-occur with impaired hearing. To our knowledge, studies providing lists of chronic diseases which do or do not relate to hearing impairment are rare. An example is a study by Crews and Campbell (Crews & Campbell, 2004) who studied 12 comorbid conditions in combination with self-reported hearing problems among community-dwelling older Americans (70⫹). It was found that ‘diabetes’, ‘arthritis’, ‘heart disease’, ‘other heart condition’, ‘stroke’, ‘fallen in the past twelve months’, and ‘being confused’ were associated with hearing loss, but ‘hypertension’, ‘depression’, ‘broken hip’, ‘injured from fall’, and ‘osteoporosis’ were not (Crews & Campbell, 2004). Although the study of Yiengprugsawan (Yiengprugsawan et al, 2012) yielded relevant information about associations between self-reported levels of hearing impairment and health outcomes in 15 to 87 year olds, detailed information about specific diseases was lost because clusters of diseases were analysed. To illustrate, a significant odds ratio was found for ‘having some trouble with hearing’ and ‘metabolic disorders’, but it was not stated whether this association was mainly caused by diabetes or by other metabolic disorder symptoms like a high cholesterol level. Most of the above described studies on hearing impairment and comorbid conditions were conducted in elderly populations. This may have caused a healthy aging bias, because it is well known that the most frail elderly are generally underrepresented in studies. Therefore it is worthwhile to confirm and determine comorbidity of chronic medical conditions in combination with hearing impairment in younger adults. More knowledge on the existence of chronic diseases cooccurring with hearing impairment is also important from a clinical perspective. Clinicians in hearing health care, like audiologists and otolaryngologists, may need to know whether their patients are likely to have other chronic conditions co-occurring with their hearing impairment. If so, this can taken into account in the rehabilitation program. Also geriatricians, and other health-care professionals may need to know whether their patients are likely to have a hearing loss, as it will have an influence in the clinical encounter. Subgroups of hearing-impaired adults with different types of chronic medical conditions may need different types of rehabilitation. Finally, there is the preventive or public health perspective for which more knowledge about chronic diseases co-occurring with hearing loss may be relevant. For example, when considering screening for hearing problems in older adults it may be (cost) effective and efficient to screen for hearing problems in samples of people suffering from a chronic condition which is highly likely to be concurrent with hearing loss. The aim of the current study was to investigate the occurrence of 27 chronic somatic medical conditions in a cohort of adults aged 18 to 70 years with and without hearing impairment, and to examine the association between the occurrence of these chronic medical conditions and hearing ability. We hypothesized a higher comorbidity in hearing-impaired adults than the occurrence of chronic diseases in adults with normal hearing.

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Materials and Methods Data collection The National Longitudinal Study on Hearing (NL-SH) is an ongoing prospective cohort study in the Netherlands, conducted via the internet since 2006. The NL-SH examines the relationships between hearing impairment and several domains in life of adults between 18 and 70 years of age. The NL-SH website (www.hooronderzoek.nl, in Dutch) is used to enroll and inform the (potential) participants and to collect data. The selection of participants was not random. Rather than constructing a representative sample of the general Dutch population, our aim was to create a convenient large sample of normallyhearing and hearing-impaired adults to serve the specific purpose of comparing normally-hearing and hearing-impaired groups of adults on a wide range of variables. We used (and still use) a variety of approaches to recruit participants. First, a link between the website of the National Hearing Test (see the next section about hearing ability in noise) and the NL-SH website exists. Every individual who is interested in his/her hearing status and performs the National Hearing Test on the web, is invited to participate in the NL-SH, and is redirected to the NL-SH website once the test is done. In addition, a link to the NL-SH study is permanently posted on a range of other websites (both hearing-related and non hearing-related). Examples are the website of the hardof-hearing patient organization and the site of association for people with late onset and/or sudden deafness. Also, flyers containing information about the study are regularly distributed in audiology clinics, at health fairs, and in hearing-aid dispenser shops in The Netherlands. Some advertisements were placed in local newspapers, and a number of participants learned about the study by word-of-mouth. Visitors to the NL-SH website can always subscribe themselves to the study. Thus, adults between 18 and 70 years of age, from all over The Netherlands, were (and still are) free to enrol themselves into the NL-SH study. Both hearingimpaired and normally-hearing people are invited to participate and there is no specific focus on recruiting one group more than the other (it is an open subscription). After subscription, participants receive an email with a link to a set of online questionnaires. An email reminder and a letter by regular mail are sent to participants who do not respond within one week or one month. More details about the study design and data collection can be found in publications by Nachtegaal et al (Nachtegaal et al, 2009 a,b). The NL-SH study is approved by the Medical Ethics Committee of the VU University Medical Center in Amsterdam, The Netherlands.

Hearing ability in noise Before enrolment in the study, participants had to perform the National Hearing Test. It examines the participants’ ability to understand digit triplets (e.g. 6-2-5) in noise (Smits et al, 2004, 2006a). Participants were instructed to perform the test in a quiet room. Either headphones or speakers were allowed to be used. At the start of the test, participants were asked to enter their age and gender, and they had to indicate whether they were using headphones or speakers. A total of 23 digit triplets were presented against a background of stationary masking noise according to an adaptive (one-up, one-down) procedure. After each incorrect response, the subsequent triplet was presented at a two-decibel higher level; if the participant provided a correct response, the subsequent triplet was presented at a two-decibel lower

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level. Listeners typed or clicked the digits on their keyboard or computer screen. When headphones were used the digits were presented to both ears (diotic). The noise level was fixed in the test and the speech level varied. The speech-reception-threshold in noise (SRTn) was calculated by taking the average signal-tonoise ratio (SNR) of the last 20 presentations, corresponding to 50% intelligibility. SRTn values ranged from ⫺ 13.4 to ⫹ 4 dB signal-to-noise ratio (dB SNR). According to reference data by Smits et al (Smits et al, 2006b) scores on the National Hearing Test were categorized in three categories: good (SRTn ⬍ ⫺ 5.5 dB), insufficient (⫺ 5.5 ⱕ SRTn ⱕ ⫺ 2.8 dB), and poor hearing ability (SRTn ⬎ ⫺ 2.8 dB). The validity and reliability of the National Hearing Test have been proven to be good (Smits et al, 2004, 2006; Smits & Houtgast, 2006b; Nachtegaal et al, 2009b).

Chronic medical conditions The presence of chronic medical conditions was assessed by means of the official list of Statistics Netherlands which was used for public health purpose in the Netherlands. This list includes a total of 27 conditions (Mootz & van den Berg, 1989). It was presented to each participant as part of the online questionnaire. The instruction was as follows: “Below you find a list of 27 chronic medical conditions or diseases. Please tick the box for a chronic condition or disease if it is present now or if it was present during the last twelve months”. A wide variety of chronic medical conditions was questioned, including diabetes, cardiovascular disease, and respiratory conditions. Figure 1 shows all included chronic medical conditions and diseases. We calculated the sum for the total number of chronic medical conditions and divided this outcome into five categories: none, one, two, three, or four or more chronic medical conditions. Self-reports of chronic

1.

Asthma or Chronic obstructive pulmonary disease (COPD)

2.

Infection of the nose or nasal sinuses

3.

Severe heart disease or heart infarction

4.

High blood pressure

5.

(Consequences of) stroke

6.

Stomach ulcer or bowels ulcer

7.

Severe bowel problems, longer than 3 months

8.

Gallstones or gallbladder infection

9.

Liver disease or liver cirrhosis

10.

Kidney stones

11.

Severe kidney disease

12.

Chronic bladder infection

13.

Prolapses of uterus, bladder, or rectum (only for women)

14.

Diabetes

15.

Thyroid disease

16.

Chronic back pain, longer than 3 months or spinal disc herniation

17.

Osteoarthritis of knees, hips, or hands

18.

Rheumatic arthritis of hands, and/or feet

19.

Other chronic arthritis, longer than 3 months

20.

Epilepsy

21.

Other conditions affecting nervous system like Parkinson’s disease

22.

Multiple Sclerosis

23.

Migraine

24.

Dizziness causing falling

25.

Malignant condition or cancer

26.

Burn-out, depression or serious nervousness

27.

Chronic skin disease or eczema

Figure 1. The chronic medical conditions or diseases included in the NL-SH questionnaire. Participants were asked if these conditions or diseases were present now or during the last twelve months (yes/no).

Comorbidity in adults with hearing impairment medical conditions are found to be fairly accurate for many diseases, like cardiac disease, stroke, and diabetes (Kriegsman et al, 1996; Tisnado et al, 2006; Skinner et al, 2005).

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Confounding variables Research has shown that socioeconomic status and/or hearing status are associated with the occurrence of chronic medical conditions. To illustrate, Mackenbach et al (Mackenbach et al, 2008) showed that groups of adults with lower socioeconomic status usually report a poorer health status than groups with a higher socioeconomic status. Markers of socioeconomic status were also found to be associated with the 10 year cumulative incidence of hearing impairment (Cruickshanks et al, 2010). Also, Sixt and Rosenhall (Sixt & Rosenhall, 1997) showed correlations between socioeconomic status and hearing impairment. Therefore, the confounding effects of age, gender, educational level, and income were examined. Educational level was divided into three levels: low (not finished elementary school to lower vocation), mid (general intermediate to general secondary), and high (higher vocational to post academic). Income was measured by asking the participants to choose their gross monthly income category: low (less than €1050), mid (between €1050 and €2550), high (more than €2550) and, unknown (do not know, do not want to report).

Participants Between November 2006 and April 2011 a baseline online questionnaire was sent to 2303 participants aged 18 to 70 years. A total of 1983 (84.8%) participants returned the questionnaire partially or totally completed (36% males, 64% females). A minority of the participants, 116 of the 1983 (5.8%), did not answer any question about having a chronic condition, therefore those participants were excluded from the analyses. Two participants were excluded because of conflicting/inconsistent responses. Besides, because of the facultative nature of the items on chronic medical conditions a participant could have blanks on many of the items. Therefore, a blank was regarded as a missing value. Consequently, although the overall sample consisted of 1865 participants, per chronic condition the number of participants who reported having a specific chronic condition varied. Per chronic condition the available data of all participants who completed that specific condition was included in the analyses. The non-responder analysis showed that the participants who did not complete the chronic medical conditions list had a slightly but significantly better hearing ability (mean difference: 0.83 dB SRTn), were younger (mean difference: 2.2 years), and had a different gender ratio (44.6% of the non-responders were men) compared to the participants included in the analyses.

Statistical analyses First of all, the prevalence of chronic medical conditions in the NL-SH study population was determined. Participants could report more than one chronic condition. To investigate the relationship between hearing status (good/insufficient/poor hearing ability in noise) and the presence of a chronic condition (yes/no), 3 ⫻ 2 tables were constructed for all 27 chronic medical conditions. Multinomial logistic regression analyses were used to further explore the relationship between those chronic medical conditions (determinants) and hearing ability (categorical outcome variable) for which significant linear-by-linear associations (Armitage, 1955) were found. Multinomial logistic regression

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analyses can be interpreted as two simultaneously performed binary logistic regression analyses. Both unadjusted and adjusted OR’s and 95% confidence intervals (95% CI) were examined. A variable was considered as a relevant confounder if the OR of a chronic condition changed with 10% or more after adding the potential confounder to the model. Additionally, the potential confounder had to be significantly associated with both the determinant (chronic condition) and the outcome (hearing ability). Age (as a continuous variable) and gender were tested for their potentially modifying effect by adding an interaction term (e.g. age * chronic condition) to the model. Stratified models were presented when the interaction term was significant (p ⬍ 0.05). All statistical analyses were performed with SPSS, version 20.0.

Results Demographic and socioeconomic characteristics of the NL-SH participants are given in Table 1. The data show that approximately one third of all participants did not state any chronic medical condition present in the last year. Having any chronic medical condition was more frequent in the group with insufficient and poor hearing than in the group with good hearing ability (on average 1.9 versus 1.5). Of the participants with poor hearing ability 78.5% reported one or more other chronic medical conditions. Approximately 28% of the participants with poor hearing ability reported one other chronic condition besides their hearing problem, and 50% had at least two other chronic conditions. Almost 15% reported to have four or more additional chronic medical conditions. Among the normally-hearing participants, 68.6% reported one or more chronic conditions and 37.7% reported two or more chronic conditions. Table 2 shows the prevalence of 27 chronic medical conditions in the NL-SH cohort. Differences in most frequently reported chronic medical conditions were found between the three hearing ability groups. As can be seen in Table 3, the top three most frequently reported chronic medical conditions in combination with poor hearing ability were: (1) infection of the nose or nasal sinuses; (2) high blood pressure; and (3) osteoarthritis of knees, hips, or hands. Infection of the nose or nasal sinuses, and high blood pressure were also the two most reported conditions in the group of participants with normal hearing. For eight chronic medical conditions (high blood pressure; diabetes; severe bowel problems; osteoarthritis of knees, hips, or hands; other chronic arthritis; infection of the nose or nasal sinuses; dizziness causing falling, and malignant condition/cancer) a significant linear-by-linear association (p ⬍ 0.05) between the presence of that condition and hearing ability was found. Table 4 shows the associations between those eight chronic medical conditions and hearing ability. Note that age and gender were identified as confounding variables and therefore included in the models. Educational level and income appeared not to confound the association between the presence of medical conditions and hearing ability and hence, were not included in the models. Age and gender were not identified as relevant effect modifiers and therefore no subgroup analyses were performed. In the unadjusted multinomial logistic regression models, significant associations for all those eight conditions and poor hearing ability were found (second column). However, after adjustment for age and gender, only some associations remained significant (fifth column). These were: ‘diabetes’ (OR: 2.14 (95% CI: 1.11–4.09; p ⫽ 0.022)), ‘other chronic arthritis’ (OR: 1.87 (95% CI: 1.10–3.19; p ⫽ 0.022)), and ‘dizziness causing falling’ (OR: 2.50

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M. Stam et al. Table 1. Descriptive statistics for demographic, socioeconomic, and health variables stratified by category of hearing ability. Hearing ability *

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Variables Demographic and socioeconomic variables Age (mean, SD), range: 18–70 years Sex Male (%) Female (%) Educational level Low (not finished elementary school to lower vocation) (%) Mid (general intermediate to general secondary) (%) High (higher education, university and post-academic) (%) Hearing status SRTn (mean, SD), range: ⫺ 13.4 to 4 dB Chronic medical conditions Total number (mean, SD), range: 0–13 None (%) One (%) Two (%) Three (%) Four or more (%)

Total (N ⫽ 1865)

Good (N ⫽ 975)

45.8 (12.6) 43.6 (12.7)

Insufficient (N ⫽ 410)

Poor (N ⫽ 480)

p-value

48.0 (11.5) 48.5 (12.5) ⬍ 0.001

35.3 64.7

39.0 61.0

30.2 69.8

32.3 67.7

0.004

18.8 33.4 47.8

13.7 34.3 52.1

21.5 29.6 48.9

26.9 35.0 38.1

⬍ 0.001

⫺ 4.6 (3.5) ⫺ 7.3 (1.1) ⫺ 4.3 (0.8) 1.7 (1.7) 27.3 29.3 19.2 11.6 12.5

1.5 (1.7) 31.4 30.9 18.3 9.5 9.9

1.9 (1.7) 24.6 27.3 17.3 14.4 16.3

0.6 (2.1) 1.9 (1.9) 21.5 27.7 22.9 13.3 14.6

⬍ 0.001 ⬍ 0.001

*According to Smits et al (Smits et al, 2006b) scores on the National Hearing Test were categorized in three categories: good (SRTn ⬍ ⫺ 5.5 dB), insufficient (⫺ 5.5 ⱕ SRTn ⱕ ⫺ 2.8 dB), and poor hearing ability (SRTn ⬎ ⫺ 2.8 dB).

(95% CI: 1.49–4.19; p ⬍ 0.001)). Note that good hearing ability was used as the reference category in these models. Table 4 (third and sixth column) additionally shows significant associations between two chronic medical conditions (‘high blood pressure’ and ‘dizziness causing falling’) and the severity of hearing impairment. As a poor hearing ability score is worse than an insufficient hearing ability score, this odds ratio described the severity of hearing impairment. In participants who reported ‘high blood pressure’, the odds for having poor hearing ability increased by a factor of 1.50 (95% CI: 1.05–2.15; p ⫽ 0.025) compared to participants without high blood pressure. For participants with ‘dizziness causing falling’ the odds ratio was 2.09 (95% CI: 1.12–3.89; p ⫽ 0.020) in the adjusted model.

Discussion This is the first study which investigated the association between hearing ability and comorbidity, using an extensive list of 27 chronic conditions. An objective speech-in-noise test was used to measure people’s hearing status. It is often argued that this is a more ecologically valid measure of hearing than pure-tone threshold testing (Kramer et al, 1996, 1998; Houtgast & Festen 2008). We found that more than two thirds of the NL-SH participants with impaired hearing (insufficient or poor hearing ability score) reported to suffer from at least one additional chronic condition (other than hearing impairment). Furthermore, it was investigated which chronic medical conditions were related to hearing ability. Our results revealed a significant association between ‘dizziness causing falling’ and poor hearing ability. Also ‘diabetes’ as well as type of arthritis other then osteoarthritis or rheumatic arthritis (‘other chronic arthritis’) were associated with poor hearing ability. ‘Osteoarthritis’ was associated with insufficient hearing ability, but ‘rheumatic arthritis’ was not associated with hearing ability. Except for the association with

‘high blood pressure’ which appeared significant in some statistical analyses, we did not find significant differences in the occurrence of cardiovascular conditions (such as, stroke, severe heart disease, or heart infarction) across hearing ability groups. Crews and Campbell (Crews & Campbell, 2004) conducted a similar study, but they included older adults only and they examined only 12 chronic conditions. Our results agree with their findings in that they also found associations between hearing impairment and diabetes, arthritis, as well as ‘fallen in the past 12 months’ and hearing impairment, and no association with high blood pressure. In contrast to our results, they observed associations with heart disease, other heart conditions, stroke, and ‘being confused’ which we could not demonstrate or test. The fact that Crews and Campbell found a larger number of chronic conditions related to self- reported hearing loss, may have been due to their older sample. Another reason for observing differences in findings is that their list of chronic conditions was slightly differently formulated. To illustrate, in the list used in the NL-SH study, arthritis was subdivided into ‘osteoarthritis of knees, hips or hands’, ‘rheumatic arthritis of hands and/or feet’ and ‘other chronic arthritis longer than 3 months’, whereas Crews and Campbell only used one category ‘arthritis’. Thus, we specified arthritis into sub-categories rather than using a global term. We found an association with hearing ability for osteoarthritis and ‘other chronic arthritis’, but not for rheumatic arthritis. Our results are in agreement with that of Crews and Campbell, only we specified it in more different types of arthritis associated with hearing ability. The significant association between hearing impairment and an increased risk of falling which we observed in the current study, is in agreement with observations in many other studies (Lin & Ferrucci, 2012; Purchase-Helzner et al, 2004; Crews & Campbell, 2004; Viljanen et al, 2009; Lopez et al, 2011). It is important to note that we found this association in a relatively young age group (18–70 years), whereas earlier studies mainly included older study populations.

Comorbidity in adults with hearing impairment

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Table 2. Prevalence of 27 chronic medical conditions in the NL-SH study, stratified per category of hearing ability. Hearing ability

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Chronic conditions present now or in the last twelve months Cardiovascular conditions (Consequences of) a stroke High blood pressure Severe heart disease or heart infarction Diabetes Digestive conditions Gallstones or gall-bladder infection Severe bowel problems ⬎ 3 months Stomach ulcer or bowels ulcer Hormone producing organ disorders Kidney stones Severe kidney disease Liver disease or liver cirrhosis Thyroid disease Malignant disease or cancer Mental condition: Burn-out, depression, or severe nervousness Musculoskeletal conditions Chronic back pain ⬎ 3 months, or spinal disc herniation Osteoarthritis of knees, hips, or hands Rheumatic arthritis of hands, and/or feet Other chronic arthritis ⬎ 3 months Respiratory conditions Asthma or Chronic Obstructive Pulmonary Disease (COPD) Infection of the nose or nasal sinuses Other chronic conditions Chronic bladder infection Dizziness causing falling Epilepsy Migraine Multiple sclerosis Other conditions affecting nervous system, e.g. Parkinson’s disease Prolepses of uterus, bladder, or rectum (only for women) Severe skin disease

No.

Overall prevalence (%)

Good

Insufficient

Poor

P-value

13 308 23 52

0.7 16.6 1.2 2.8

0.6 14.7 1.0 1.9

1.0 15.4 1.7 3.2

0.6 21.5 1.3 4.4

– 0.002 ns 0.005

101 78 28

5.5 4.2 1.5

5.1 3.4 1.7

5.7 4.2 0.7

6.1 5.9 1.9

ns 0.034 ns

18 7 14 87 27 266

1.0 0.4 0.8 4.7 1.5 14.4

0.8 0.5 1.0 5.0 0.9 14.1

0.5 No cases No cases 4.4 1.7 13.8

1.7 0.4 0.8 4.4 2.3 15.6

– – – ns 0.035 ns

283 294 94 82

15.3 15.9 5.1 4.4

13.2 11.9 4.5 2.9

19.6 20.6 6.4 5.9

16.0 19.9 5.3 6.3

ns ⬍ 0.001 ns 0.001

238 417

12.8 22.5

11.8 19.7

15.9 26.7

12.3 24.5

ns 0.017

29 79 21 273 6 9 49 235

1.6 4.3 1.1 14.9 0.3 0.5 2.7 12.7

1.6 3.0 1.5 13.7 0.3 0.6 2.5 12.1

2.3 7.4 0.6 15.1 0.6 0.4 4.0 12.2

ns ⬍ 0.001 ns ns – – ns ns

0.7 3.7 1.0 17.4 No cases 0.2 1.5 14.8

ns: Non-significant linear-by-linear association (p ⬎ 0.05) - Too small a number of cases per Hearing Test category to test an linear-by-linear association.

Although it was not measured in our questionnaire whether a fall was disabling and the underlying mechanism for falling was not studied, our study expands on the evidence for this association. Furthermore, current results confirm an association between diabetes and hearing impairment (Maggi et al, 1998; Helzner et al, 2005; Crews & Campbell, 2004; Bainbridge et al, 2008; Agrawal et al, 2008). Again, our study is a useful addition to the literature as we found this association in a younger age group. An interaction effect for age was not found, endorsing conclusions of a recent metaanalyses showing that the association between diabetes and hearing ability is not different for different ages (Horikawa et al, 2013). An investigation of the mechanisms underlying the associations between hearing impairment and diabetes was beyond the purposes of this study and needs to be investigated in future research. Whereas other studies reported on an association between high blood pressure and poor hearing ability (Crews & Campbell, 2004; Agrawal et al, 2009; Rosenhall & Sundh, 2006), our results did not show such an association, after adjustment for age and gender. Although participants with high blood pressure had significantly higher odds for decreased hearing ability (poor hearing ability versus insufficient hearing ability), no significant odds ratio was found for

the more severe hearing disability (poor hearing ability versus good hearing ability). Apparently, age was a dominant confounding factor in the relationship between high blood pressure and hearing ability. Our results are in concordance with some other studies (Fransen et al, 2008; Torre et al, 2005) which failed to show an association between pure-tone hearing loss and hypertension. We did not find any associations with severe heart disease or heart infarction; gallstones or gall-bladder infection; severe bowel problems; stomach ulcer or bowels ulcer; thyroid disease; malignant disease or cancer; burn-out, depression or severe nervousness; chronic back pain or spinal disc herniation; rheumatic arthritis; asthma or COPD; chronic bladder infection; epilepsy; migraine; prolepses of uterus, bladder or rectum; severe skin disease; and hearing ability. In some other studies, associations with for example psychosocial health (Nachtegaal et al, 2009b) and thyroid disease (Santos et al, 2010) were found, but we could not demonstrate these in the current study. This might be explained by differences in study population, by the measurements used, or the way comorbidity was determined. For instance, the item in the questionnaire to determine the presence of mental health problems (defined as burn-out, depression, or serious nervousness) is a fairly unsatisfactory question as it can contains

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M. Stam et al.

Table 3. Top three most reported chronic medical conditions in the NL-SH study per category of hearing ability.

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Good hearing ability 1 Infection of the nose or nasal sinuses 2 High blood pressure 3 Burn-out, depression, or severe nervousness Insufficient hearing ability 1 Infection of the nose or nasal sinuses 2 Osteoarthritis of knees, hips, or hands 3 Chronic back pain ⬎ 3 months, or hernia Poor hearing ability 1 Infection of the nose or nasal sinuses 2 High blood pressure 3 Osteoarthritis of knees, hips, or hands

19.7% 14.7% 14.1% 26.7% 20.6% 19.6% 24.5% 21.5% 19.9%

more than one option, and it can be interpreted by the respondent in many ways. Nevertheless, we kept his question as it was part of the standard list used by Statistics Netherlands. In an earlier study, we examined the concepts of depression and distress in relation to hearing ability using more precise and adequate measures (Nachtegaal et al, 2009b). For six chronic conditions (more specifically the items of stroke, liver disease or liver cirrhosis; other conditions affecting nervous system; severe kidney disease; kidney stones; and multiple sclerosis), statistical analyses could not be performed due the small number of participants reporting these conditions. The comorbidity of hearing impairment with these conditions needs further investigation. It should be mentioned that the NL-SH study was not set up to draw a representative sample of the Dutch population, as stated earlier, but rather to create a large convenient sample to serve the specific purpose of comparing normally-hearing and hearing-impaired groups of adults on a wide range of variables. A preconception about internet methods is that internet samples are not demographically

diverse (Krantz & Dalal, 2000). However, in a study by Gosling et al (Gosling et al, 2004), who compared a large web-based sample with traditional paper-and-pencil methods, it was found that the internet sample was relatively more diverse with respect to gender, socioeconomic status, geographic region, and age. We can confirm this finding, as the NL-SH cohort consists of a diverse composition of participants. But, we observed that more women than men participated in the current study, and that the proportion of adults with a higher educational level was larger than in the general population (NL-SH study: 47.8%; general Dutch population between 15 and 65 years in 2011: 27.6%). Due to these characteristics, our results are less generalizable to the general population. But still our data provide valuable and novel information. The analyses were performed in groups of a reasonable size of participants for statistical testing (rule of thumb ⬎ 20 participants) and the associations between hearing ability and chronic conditions were controlled for relevant confounders. In addition, although our cohort is not representative for the general Dutch population, it seems fairly representative for its source population of internet users. It is known that internet users in general are more likely to have a higher educational level, and are more likely to be young women than young men. Also, older men are more likely than older women to be online (Fallows, 2005, SCP 2007). Given that the current study was a web-based study, one may wonder why we did not have a much larger sample size than the N of 1865 in the current study. In theory every adult between 18 and 70 years of age, who has access to the internet and who is able (mentally and technically) to fill in our online questionnaire in Dutch can subscribe himself or herself. The main obstacle to conducting internet based research (and research in general) is finding people who are willing to participate (Crump et al, 2013). Although the accessibility to internet at home in the Netherlands is one of the highest percentages in the world (InternetWorldStats, 2012), our experience is that it is still necessary to advertize and organize national public campaigns

Table 4. Associations between several chronic medical conditions and hearing ability: Results from multinomial logistic regression analyses. Unadjusted OR (95% CI)

Chronic condition High blood pressure Diabetes Severe bowel problems ⬎ 3 months Osteoarthritis of knees, hips, or hands Other chronic arthritis ⬎ 3 months Infection of the nose or nasal sinuses Dizziness causing falling Malignant disease or cancer

Age and gender adjusted OR (95% CI)

Insufficient vs. good hearing ability*

Poor vs. good hearing ability *

Poor vs. insufficient hearing ability*

Insufficient vs. good hearing ability*

Poor vs. good hearing ability *

Poor vs. insufficient hearing ability*

1.05 (0.76–1.46) p: 0.745 1.74 (0.84–3.58) p: 0.134 1.23 (0.68–2.23) p: 0.502 1.93 (1.42–2.63) p ⬍ 0.001 2.10 (1.20–3.67) p: 0.009 1.48 (1.13–1.94) p: 0.005 1.23 (0.65–2.32) p: 0.526 1.85 (0.68–5.00) p: 0.225

1.60 (1.20–2.11) p: 0.001 2.45 (1.29–4.64) p: 0.006 1.75 (1.05–2.94) p: 0.033 1.85 (1.37–2.49) p ⬍ 0.001 2.25 (1.33–3.82) p: 0.003 1.32 (1.01–1.71) p: 0.038 2.55 (1.54–4.23) p ⬍ 0.001 2.52 (1.04–6.12) p: 0.041

1.51 (1.07–2.14) p: 0.019 1.41 (0.70–2.85) p: 0.342 1.43 (0.77–2.65) p: 0.255 0.96 (0.69–1.33) p: 0.790 1.07 (0.62–1.87) p: 0.802 0.89 (0.66–1.21) p: 0.459 2.08 (1.12–3.87) p: 0.021 1.36 (0.52–3.54) p: 0.528

0.88 (0.63–1.24) p: 0.474 1.56 (0.75–3.25) p: 0.233 1.17 (0.64–2.14) p: 0.612 1.41 (1.02–1.96) p: 0.040 1.74 (0.99–3.05) p: 0.055 1.43 (1.09–1.89) p: 0.010 1.20 (0.63–2.27) p: 0.585 1.34 (0.49–3.67) p: 0.564

1.33 (0.99–1.78) p: 0.058 2.14 (1.11–4.09) p: 0.022 1.68 (1.00–2.84) p: 0.052 1.30 (0.95–1.78) p: 0.103 1.87 (1.10–3.19) p: 0.022 1.29 (0.99–1.68) p: 0.062 2.50 (1.49–4.19) p ⬍ 0.001 1.83 (0.74–4.49) p: 0.189

1.50 (1.05–2.15) p: 0.025 1.37 (0.67–2.78) p: 0.389 1.44 (0.78–2.67) p: 0.248 0.92 (0.65–1.30) p: 0.645 1.08 (0.62–1.88) p: 0.794 0.90 (0.66–1.22) p: 0.489 2.09 (1.12–3.89) p: 0.020 1.36 (0.52–3.55) p: 0.532

Reference category: chronic condition not present. OR: odds ratio. 95% CI: 95% confidence interval. Significant associations (p ⬍ 0.05) are highlighted (in bold text). *According to Smits et al (Smits et al, 2006b) scores on the National Hearing Test were categorized in three categories: good (SRTn ⬍ ⫺ 5.5dB), insufficient (⫺ 5.5 ⱕ SRTn ⱕ ⫺ 2.8 dB), and poor hearing ability (SRTn ⬎ ⫺ 2.8 dB).

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Comorbidity in adults with hearing impairment in order to inform a large number of potential participants about the study. The NL-SH study relies on volunteers who are not financially compensated for their effort. It might be that for some people, this is a reason to not participate or to not fully complete the questionnaire (Crump et al, 2013). We did not find an association between high blood pressure and hearing ability. One might question whether an online speech-innoise test with a fixed bandwidth is an adequate measure to detect associations between hearing ability and the presence of high blood pressure. According to Gates et al (Gates et al, 1993) and Rosenhall and Sund, (Rosenhall & Sund, 2006), mainly the low frequencies (250–1000 Hz) are affected in older people with high blood pressure. Rosenhall and Sund found that hearing loss (PTA) was correlated with high blood pressure, mainly in older women. Note that the bandwidth of the digits in noise in the current study was between 300 and 3400 Hz, roughly including the frequencies referred to by Rosenhall and Sund. This means that the possible impact of high blood pressure on the lower frequencies could have been detected. Hence, we argue that the absence of a relationship in our study is not because of a limitation in the test we used to measure hearing ability. On the other hand it is true that hearing problems due to highest frequencies losses (⬎ 3400 Hz) or due to a conductive hearing loss are not being detected in the test (Smits et al, 2004). It should be mentioned that the National Hearing Test measures in essence something different (or additional) to a pure-tone audiogram. The speech-in-noise test is a more general generic measure of auditory capability that represents hearing problems in daily life more closely than pure-tone audiometry (Houtgast & Festen 2008). The diagnostic value better fits the problems people with hearing impairment experience in their daily life (Smits et al, 2004).

Possible limitations The issue of multiple statistical testing should be considered, as we examined the associations between many chronic medical conditions and hearing ability. Some statistically significant associations may have emerged by chance. Hence, it is worth considering the p-values in the multinomial logistic regression analyses and further subdivide these into three categories and interpret them as follows: p ⬎ 0.05 indicating no statistically significant association, 0.01 ⬍ p ⬍ 0.05 indicating a significant association which should to be duplicated in future studies, and p ⬍ 0.001 considered as statistically significant. In the light of these interpretations, the association between ‘dizziness causing falling’ and poor hearing ability can be regarded as relatively strong (OR ⬎ 2) and well established (p ⬍ 0.001). The associations between diabetes and poor hearing ability, and between ‘other types of arthritis other than osteoarthritis and rheumatic arthritis’ and poor hearing ability fall into the middle category (p ⬍ 0.05), indicating that confirmation in future studies is recommended. The non-responder analysis showed that young, male, and normally-hearing persons were relatively under-represented in the current sample, compared to the original sample. Although the response bias was significant for three variables, we regard it as too small for having a considerable effect on the results. As in many previous studies, cross-sectional data were used. Hence, we are unable to distinguish between cause and effect. Current results show associations between hearing impairment and some chronic diseases, which give an idea about the relationship, but not yet about the direction or underlying causes. These underlying causes of comorbid diseases are often difficult to distinguish. Questions like “Is disease A causing disease B, or is the association between disease

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A and B partly explained by another disease?” remain unanswered. As mentioned, these should be addressed in future studies. Finally, one may wonder whether the measurement of chronic medical conditions is accurate and reliable when it is self-reported. There are several studies which addressed this issue (Kriegsman et al, 1996; Tisnado et al, 2006; Skinner et al, 2005). It was consistently found that in (older) adults patients’ self-reports were fairly accurate for several conditions. In particular the self-reported presence of cardiac disease, stroke, and diabetes were found to be in agreement with medical records (Kriegsman et al, 1996). Peripheral atherosclerosis and osteoarthritis/rheumatoid arthritis were exaggerated by self-report. This might be explained in the labeling of the disease and the way it is used in informal language. In addition, for some chronic conditions recall bias could have occurred to some extent. It seems likely that people not recalling conditions within the last year (given that they did not use any medication for it or received another form of treatment) is higher than that they reported chronic conditions they did not have. It might be that our association between hearing and ‘dizziness causing falling’ is an underestimation of the real association. We consider the effect of recall bias in the relationship between hearing ability and diabetes as small. Note that in Kriegsman et al, 1996 and Skinner et al, 2005 diabetes appeared to have the highest level of concordance between the patients’ self report and medical records. In addition, around 65% of the NL-SH participants with self-reported diabetes reported to have used any medications for diabetes in the last month. As insulins and other blood-glucose lowering drugs are not used in the treatment for other conditions, and the fact that in some cases diabetes is manageable with only dietary advice and physical activity, this finding underlines the reliability of our self-report data. Although the type of diabetes (insulin dependent or not) was not examined in the NL-SH questionnaire, it was found that two third of the diabetic respondents used other blood-glucose lowering drugs (not insulin), suggesting that most NL-SH respondents who reported diabetes had in fact type 2 diabetes.

Implications Our finding that participants with impaired hearing were more likely to present comorbid conditions than their normally-hearing peers has important implications for hearing care. Comorbidity is known to be an important factor in the self-assessment of hearing impairment. Different chronic medical conditions (including hearing impairment) may differentially impact on an individual’s quality of life. To illustrate, Sprangers et al (Sprangers et al, 2000) found that the adverse effects of cerebrovascular/neurologic conditions, renal disease, or musculoskeletal conditions on well-being were greater than the effects of hearing impairments on well-being. So, for clinicians it is important to keep comorbidity in mind in the clinical encounter. With the expected increase in the prevalence of diabetes worldwide (Danaei et al, 2011) and the growing evidence that diabetes and hearing impairment are associated, further consideration of (the consequences of) diabetes in hearing health care is recommended. It is suggested to screen diabetic patients for hearing problems during their annual check-up (Davis1). Multidisciplinary cooperation and collaboration between clinicians in hearing and diabetic care as well as other disciplines should be considered as it may be beneficial and (cost) effective. Patients who suffer from multiple diseases rely on, and benefit from, not only specialized medical care, but also from care in which expertise is integrated from different disciplines for instance with regard to differential diagnostics and parallel

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treatments. The current data show that the association between diabetes as well as ‘dizziness causing falling’ and hearing impairment is not only observed in older age groups, but it is also evident in younger age groups, starting with the age of 18 years.

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Conclusions As comorbidity seems to be highly prevalent in combination with hearing impairment, it is an important topic for both hearing healthcare professionals and researchers in the field of audiology. In the current study it was found that chronic medical conditions were more prevalent among adults aged 18 to 70 years with impaired hearing than in their normally-hearing peers. A total of 27 chronic conditions, besides hearing impairment, were examined. Our results show that the previously reported relationships with hearing impairment for diabetes, dizziness causing falling, and some types of arthritis not only occur in older age groups, but also in younger cohorts. Future (prospective) clinical studies are needed to confirm these associations, to take influences of lifestyle into account, and to investigate the underlying mechanisms. Comorbidity is relevant in the rehabilitation (multidisciplinary care) and the clinical encounter of hearingrelated professionals, and also for health-care professionals who treat other conditions than hearing impairment.

Note 1. Davis A. 2012, June. Adult Hearing Screening: Health Policy Issues. Keynote lecture at the Adult Hearing Screening conference, Cernobbio, Italy.

Acknowledgements The authors thank the participants of the National Longitudinal Study on Hearing. We also acknowledge the assistance of Hans van Beek in managing the database and developing and maintaining the study website. The current results were presented at conferences, such as the Adult Hearing Screening conference in Como, Italy (June 12, 2012), the Netherlands conference on Public Health (April 12, 2012), and during the annual meetings of Dutch Audiologists (January 30, 2012) and Dutch Otolaryngologists (November 9, 2012). We thank the anonymous reviewers for their valuable comments on an earlier version of this manuscript. Declaration of interest: The NL-SH study is financially supported by Phonak AG, Switzerland. None of the authors has a conflict of interest.

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