Diabetes and Hearing Impairment in the United States: Audiometric Evidence from the National Health and Nutrition Examination Survey, 1999 to 2004

Context Previous studies have hinted at an association between diabetes mellitus and hearing impairment. Contribution Using data from a national survey, the investigators found a higher prevalence of hearing impairment among persons with diabetes than in those without diabetes (21% vs. 9%). Caution Diabetes was self-reported and was verified in only a small proportion of participants. The investigators did not distinguish between type 1 and type 2 diabetes. Implication Hearing impairment is common among adults with diabetes. The Editors Hearing loss, reported by more than 17% of the U.S. adult population, is a major public health concern affecting more than 36 million people (1). Risk for hearing impairment is associated with male sex, lower education, industrial or military occupation, and leisure time noise exposure (24), and prevalent hearing impairment has been correlated with smoking (5). Prevalence varies substantially by age, sex, and race, and estimates exceed 30% among those age 65 years or older (1). In 1 community-based study, 46% of the population age 43 to 84 years was classified as hearing-impaired on the basis of audiometric examination (6). These high-prevalence estimates imply that many people are at risk for functional and psychosocial limitations associated with hearing impairment (7, 8). Diabetes mellitus affects an estimated 9.6% of the U.S. adult population (9, 10) and is associated with microvascular and neuropathic complications affecting the retina, kidney, peripheral arteries, and peripheral nerves (11). The pathologic changes that accompany diabetes could injure the vasculature or the neural system of the inner ear, resulting in sensorineural hearing impairment. Two studies (12, 13) described evidence of such pathologic changes, including sclerosis of the internal auditory artery, thickened capillaries of the stria vascularis, atrophy of the spiral ganglion, and demyelination of the eighth cranial nerve among patients with diabetes in whom autopsy was done. Clinical evidence supporting an association between diabetes and hearing impairment is limited to several small studies (1418) or noise-exposed samples (19). Epidemiologic evidence from 1 population-based cohort study suggested a modest association (20). We used recent national survey data to examine the relationship between diabetes and hearing impairment. Specifically, we designed this analysis to determine whether hearing impairment is more prevalent among U.S. adults who report a diagnosis of diabetes than those who report no diagnosis and whether differences in prevalence by diabetes status occur predominantly in specific U.S. population subgroups. Methods Participants Data from NHANES (National Health and Nutrition Examination Survey) were collected by the National Center for Health Statistics from 1999 to 2004 by using a complex, multistage, probability sample designed to represent the civilian, noninstitutionalized U.S. population. Half of the study participants (n = 11405) age 20 to 69 years were randomly assigned to audiometric testing. Of the 5742 assigned, we included 5140 (89.5%) persons who completed the audiometric examination and the diabetes questionnaire in this analysis. Major reasons for not completing an examination included time limitation (n = 128 [2.2%]), physical limitation (n = 60 [1.0%]), communication problem (n = 42 [0.7%]), refusal (n = 81 [1.4%]), and equipment failure (n = 47 [0.8%]). Included among the 60 participants with a physical limitation is an unknown number of participants who were not tested because they could not remove their hearing aids; 7 of these participants reported diabetes. Measures As part of the NHANES survey, pure tone air conduction hearing thresholds were obtained for each ear at frequencies of 500, 1000, 2000, 3000, 4000, 6000, and 8000 Hz. Higher frequencies are perceived as higher pitches. Audiologists usually consider tones of 500 Hz or less to be low frequency, tones from 1000 to 2000 Hz to be of mid-range frequency, and tones of 3000 Hz or greater to be high frequency. The measurements were collected by trained audiometric technicians by using a calibrated audiometer that met accepted standards (Appendix). We derived measures of hearing impairment for 2 ranges of frequency (low or mid and high) and 2 categories of severity (mild or greater and moderate or greater). To produce low- or mid-frequency pure tone averages, we averaged pure tone thresholds (the signal intensities needed to perceive the tones) measured at 500, 1000, and 2000 Hz for each individual and ear (21). We averaged pure tone thresholds measured at 3000, 4000, 6000, and 8000 Hz (22, 23) for each individual and ear to produce high-frequency pure tone averages. For each frequency range, a pure tone average greater than 25 decibels hearing level (dB HL) defined hearing impairment of mild or greater severity, whereas a pure tone average greater than 40 dB HL defined hearing impairment of moderate or greater severity (24). For each combination of frequency range and severity, we defined hearing impairment in terms of the pure tone average in the worse ear, which designates persons with impairment in at least 1 ear. We also defined hearing impairment in terms of the better ear, which designates persons with impairment in both ears (a subset of the persons impaired in at least 1 ear). Table 1 shows functional descriptions of hearing impairment, by frequency range and severity. In addition, we classified participants as having self-reported hearing impairment if they reported having a little trouble hearing, having a lot of trouble hearing, or being deaf without a hearing aid (1). Table 1. Functional Description of Hearing Impairment, by Severity of Impairment and Frequency Range Among the 5140 participants, the National Center for Health Statistics identified 24 participants with at least 1 audiometric nonresponse (that is, participants did not perceive the pure tone at any level of intensity). We classified these cases as impaired for a frequency range if the audiometric nonresponse occurred within the range. An examination of these participants' available pure tone thresholds corroborated their classification as impaired at both levels of severity. Information on demographic characteristics, diagnosed diabetes, noise exposure, medication use, and smoking was obtained during in-home interviews. Education was assessed as the highest grade level or degree attained. Incomepoverty ratio was defined as the ratio of reported total family income to the U.S. Census Bureau poverty threshold, which varies by family size and age of family members. Diagnosed diabetes was assessed with the question, Other than during pregnancy (for women), have you ever been told by a doctor or health professional that you have diabetes or sugar diabetes? Of the 5140 participants, 2259 received an additional random assignment to a fasting protocol and subsequent blood draw. Of the 2259 participants, 146 reported a diagnosis of diabetes. Of the remainder, 73 participants were classified as having undiagnosed diabetes (fasting plasma glucose level 7 mmol/L [126 mg/dL]) and 539 were classified as having impaired fasting glucose (fasting plasma glucose level 5.6 mmol/L [100 mg/dL], but <7 mmol/L [<126 mg/dL]). The remaining 1501 participants were defined as having normal glycemic status. Occupational noise exposure was defined as reporting a history of loud noise at work that required speaking in a loud voice to be heard. Leisure-time noise exposure was based on participant recall of noise from firearms (outside of work) or other sources (such as loud music or power tools) for an average of at least once a month for 1 year. History of military service was determined from a question asking about ever having served in the U.S. Armed Forces. Use of ototoxic medications was assessed by a review of medication containers. Because the small proportion of adults reporting use of aminoglycoside antibiotics (0.03%), loop diuretics (1.5%), antineoplastic drugs (5.0%), and nonsteroidal anti-inflammatory drugs (7.3%) precluded analysis of these medications individually, we defined use of ototoxic medication as use in the past 30 days of any of these 4 drug classes. Statistical Analysis Differences in the distribution of sociodemographic characteristics, military history, noise exposure (leisure time and occupational), ototoxic medication use, smoking, and diagnosed diabetes were tested by using the t test (for continuous characteristics) or chi-square test (for categorical characteristics). Unadjusted prevalence estimates and 95% CIs for the hearing impairment outcomes were assessed by diagnosed diabetes status. Prevalence estimates were additionally stratified by sociodemographic characteristics, military history, leisure-time noise exposure, occupational noise exposure, ototoxic medication use, and smoking to identify population subgroups that may be particularly vulnerable to diabetes-related hearing impairment. Age-adjusted prevalence estimates were computed by direct standardization to the 2000 U.S. Census population by using age categories of 20 to 49 years, 50 to 59 years, and 60 to 69 years. Statistical significance of the difference between unadjusted estimates was determined from chi-square test statistics for a general association, and the CochranMantelHaenszel chi-square test was used to determine the statistical significance of the difference between age-adjusted estimates. For the 2259 participants who had been randomly assigned to the fasting protocol, age-adjusted prevalence estimates of high-frequency hearing impairment were generated by glycemic status (diagnosed diabetes, undiagnosed diabetes, impaired fasting glucose, or normal). Odds ratios (with 95% CIs) for the independent association of diabetes with hearing impairment were estimated by using multiple logistic regression models, adjusting for age, sex, race or ethnicity, education,