Behind cardiovascular disease and arthritis, hearing loss is the third most prevalent chronic health condition in adulthood.1 There are numerous possible causes of hearing loss, which include repeated exposure to hazardous levels of noise, viral-based diseases, ototoxic medications, neurochemical changes, anoxia, smoking, cardiovascular disease, and genetics, and although some of these predisposing factors are not modifiable (e.g., genetics), some are preventable.
In addition to promoting hearing aid use among individuals with hearing loss, one additional strategy includes the promotion of physical activity to reduce the likelihood of developing cardiovascular disease. Arteriosclerosis can reduce blood circulation through the inner ear, particularly the cochlea. Reductions in cochlear blood flow may influence the availability of oxygen and glucose, which may reduce hearing acuity.3
This assertion is supported by two studies reporting increased hearing loss among individuals with arteriosclerosis.4, 5 Considerable research demonstrates that regular participation in moderate-to-vigorous physical activity (MVPA) can prevent the development of atherosclerotic vascular disease, and in theory, play a role in maintaining hearing function in late adulthood.6, 7
We were unable to locate any previous study investigating the association between objectively measured physical activity and hearing function in adults. However, shedding some light into this issue, Cristell and colleagues examined whether eight weeks of aerobic exercise training improved hearing sensitivity through improvements in cardiovascular fitness. Among the 17 moderately low fit young adults, the eight-week bicycle ergometer training at 70% of peak oxygen consumption improved pure-tone hearing.8
Additionally, Ismail and colleagues showed that improved cardiovascular fitness may influence hearing sensitivity through the resistance to hearing impairment resulting from noise exposure.9 Compared with participants in the control group, participants in the experimental group who underwent an eight-month program of aerobic exercise recovered significantly faster, from temporary auditory fatigue after exposure to the controlled 110-dB noise.
In this study, we used a representative sample of the non-institutionalized US population to specifically examine whether objectively measured physical activity is associated with hearing function among older adults (50+ yrs). Given that hearing loss, although not as prevalent, does occur in adolescents and younger and middle-age adults, a secondary aim was to examine whether a relationship between objectively measured physical activity and hearing sensitivity exists in these age groups as well.10
Design and participants
Data from the 2003-2006 National Health and Nutrition Examination Survey (NHANES) was used in the analyses. The final study sample included 1,880 NHANES participants, after the exclusion of participants who had insufficient accelerometry data, missing audiometry data from non-tested participants, audiometry data with non response, audiometry data that was not obtainable, individuals who had a cold, sinus, or ear ache in the 24 hours prior to audiometry testing, exposed to loud noise or listened to music with headphones in the 24 hours prior to audiometry testing, and those with impacted cerumen.
Measurement of physical activity
Participants six years of age or older who were not prevented by walking impairments wore an ActiGraph 7164 accelerometer. Participants were asked to wear the accelerometer on the right hip for seven days following their examination. Activity counts were summarized in one-minute time intervals.
A weighted average of four accelerometer-derived intensity-related count cut-points was used to classify moderate and vigorous physical activity intensity. The threshold for moderate intensity was 2020 counts and the threshold for vigorous intensity was 5,999 counts. Accelerometry data were reduced to mean duration (in minutes) of MVPA bouts accumulated over one- and 10-minute intervals. Only those participants with at least four days with 10 or more hours per day of monitoring data were included in the analysis.11
Measurement of hearing ability
Audiometry was conducted in a dedicated, sound-isolating room by a trained examiner on participants aged 20-69 years in the NHANES 2003-2004 cycle, and those aged 12-19 years and 70-85 years in the NHANES 2005-2006 cycle, using a modified Hughson Westlake procedure for measuring pure-tone detection thresholds. Prior to, and after audiometry testing, the audiometer was calibrated according to manufacturer specifications.
Hearing threshold testing was conducted on both ears of the participants at seven frequencies (500, 1000, 2000, 3000, 4000, 6000, and 8000 Hz) across an intensity range of -10 to 120 dB. For the 2003-2006 NHANES cycles, masking was not employed because of the complexity of the procedure. However, a cross-over retesting protocol was performed whenever the observed threshold at any given frequency was poorer in one ear than the other by 25 dB at 500 Hz and 1000 Hz, or 40 dB at any higher frequency. Retesting was accomplished using insert earphones, which are smaller and have less direct contact with the head; thus, a much louder stimulus is required before cross-over occurs.12
Consistent with previous hearing studies of NHANES data, low-frequency pure-tone average (LPTA) was obtained by calculating the average of air conduction pure-tone thresholds at 500, 1000, and 2000 Hz and high-frequency pure-tone average (HPTA) was obtained by the average of the air conduction pure-tone thresholds at 3000, 4000, 6000, and 8000 Hz. Measures of hearing loss were categorized according to the hearing sensitivity in the worse ear and defined as good hearing (LPTA or HPTA <16 dB), some hearing loss (LPTA or HPTA 16-24 dB), and worse hearing loss (LPTA or HPTA >24 dB).13–16
Information about age, gender, race/ethnicity, education, marital status, and smoking status were obtained from a questionnaire during a household interview. Trained household interviewers administered the questionnaire with interview data recorded using a Blaise format computer-assisted personal interview (CAPI) system. During examination, body mass index (BMI) was calculated from measured weight and height.
All statistical analyses were performed using procedures from sample survey data using STATA to account for the complex survey design used in NHANES. Data from NHANES 2003-2004 and 2005-2006 were combined, and to account for oversampling and non-response, all analyses included the use of appropriate sample weights. Means and standard errors by hearing ability categories were calculated for continuous variables and proportions were calculated for categorical variables (Tables 1 and 2).
Statistical differences in the continuous variables were tested using an adjusted Wald test, while differences between categorical variables were tested with design-based likelihood ratio chi-square tests. Differences in time spent in MVPA (both one- and 10-minute bouts) across hearing function were tested using an adjusted Wald test and were adjusted for age, gender, race/ethnicity and BMI (Table 3).
Multinomial logistic regression (MNLR) was used to examine the association between mean duration of MVPA and hearing function. Four age-specific separate MNLR models were computed: all participants (12-85 years); only adolescents (12-19 years); young- and middle-age adults (20-49 years); and only older adults (50-85 years). Consistent with previous studies showing that age, gender, race/ethnicity, and smoking status are associated with both physical activity and hearing function, these variables were adjusted for in the MNLR models.17
Table 1 shows the demographic characteristics of the NHANES analytical sample stratified by hearing status. Except for height, there were significant differences among participants with good hearing compared to worse hearing, with respect to age, gender, weight, BMI, diabetes status, race/ethnicity, education, smoking status, and marital status.
Participants with good hearing (7.27 ± 0.25 dB) and some hearing loss (12.03 ± 0.5 dB) had a significantly better low frequency pure tone threshold than participants with worse hearing (24.78 ± 0.61). Additionally, participants with good hearing (8.91 ± 0.2 dB) and some hearing loss (19.18 ± 0.19 dB) had a significantly better high frequency pure tone threshold than participants with worse hearing (49.3 ± 1.06).
The percentage of participants in each hearing classification across each age group is displayed in Table 2. As expected, the majority of participants with worse hearing were older participants (50-85 years, 75.5%); the majority of participants with some hearing loss were young- and middle-age adults (20-49 years, 25.3%); and the majority of participants with good hearing were adolescents (12-19 years, 81.7%).
Mean MVPA bouts are displayed in Table 3. Among each separate age group, and for all ages combined, there were no significant differences between hearing function after adjusting for age, gender, race/ethnicity, and BMI.
The MNLR results for the association between physical activity (MVPA) across hearing function among all participants are displayed in Table 4. After adjustment for age, gender, smoking, and race/ethnicity, no statistically significant associations emerged for one-minute bouts or 10-minute bouts when good hearing was compared with worse hearing. Similar results occurred when models were run separately for each age group.
Additionally, we treated hearing sensitivity as a continuous measure and there were no significant associations between MVPA and low frequency pure tone threshold and high frequency pure tone threshold, or at each of the seven frequencies.
These findings are important as costly physical activity-based interventions are being developed for individuals with hearing limitations.8 Regular participation in physical activity may, in theory, preserve hearing function by increasing cardiovascular function and reducing the likelihood of developing cardiovascular disease, but before cost-effective interventions are developed, it is important to first determine whether an association between physical activity and hearing sensitivity exists. Our findings show that there was no association.
Similarly, we observed no relationship between physical activity and hearing sensitivity in adolescents and young and middle-age adults. Although we found no association between physical activity and hearing sensitivity, it is still recommended that individuals with hearing limitations engage in physical activity on a regular basis, as regular participation in physical activity in adults is associated with a number of positive health outcomes, including the reduction in risk of many chronic diseases, such as adiposity, coronary heart disease, hypertension, stroke, depression, type 2 diabetes, and certain cancers.18 In partial support of this, our univariate analyses showed that participants with good hearing had significantly lower BMI levels than those with some hearing loss or worse hearing.
Given that no studies to date have investigated the relationship between physical activity and hearing sensitivity among adults, it is difficult to compare our results with other studies. However, in contrast to our findings, Alessio and colleagues examined the association between cardiovascular fitness and hearing sensitivity among 154 participants, ranging in age from 12-84 years, and showed that participants 50 years of age and older with high cardiovascular fitness had better hearing sensitivity, than individuals with low cardiovascular fitness.19
Importantly, in the Alessio et al. study, as well as other studies supporting a link between cardiovascular fitness and hearing function, age was controlled for, but additional confounding variables, such as gender, race/ethnicity, and smoking were not.8,20,21 It is likely that the relatively small sample in these studies prevented the ability to control for such co–variates.
Due to insufficient NHANES cardiorespiratory data, we were unable to examine the association between cardiovascular fitness and hearing sensitivity. Among the few studies reporting a link between cardiovascular fitness and hearing function, the authors have proposed that the biological mechanisms through which cardiovascular fitness may exert a protective effect on preserving hearing sensitivity over time, may occur through changes in blood circulation, prevention of neurotransmitter loss, and attenuation of noise-induced auditory damage.
Limitations of this study include the cross-sectional study design, which precludes the ability to make causal inferences regarding the temporal relationship between physical activity and hearing sensitivity. Thus, our null findings may in part be due to the fact that we were not able to determine the physical activity level prior to the hearing loss.
We can conclude, however, that there are no differences in physical activity levels among people who have worse hearing compared with people who have good hearing. Furthermore, the major strength of this investigation was availability of objectively measured physical activity and objectively-measured hearing sensitivity in adolescents and adults of all ages using a nationally representative sample.
In summary, our results do not provide a link between physical activity and hearing sensitivity. Before conclusions can be made regarding the association between cardiovascular fitness and hearing sensitivity, additional studies that can determine temporality and control for possible confounders are needed.
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