Disease Strongly Linked to Hearing Impairment, but Mechanism Unclear
By Jill Stein
CHICAGO—Investigators from the National Institutes of Health (NIH) are now recommending that physicians encourage their patients with diabetes to have their hearing checked.
The recommendation is based onthe results of audiometric testing ina large sample of patients with diabetes enrolled in the National Healthand Nutrition Examination Survey (NHANES).
"We found that hearing impairment was 2-fold greater in people with diabetes compared with people without diabetes," Catherine C. Cowie, PhD, director of the Diabetes Epidemiology Program at the National Institute of Diabetes and Digestive and Kidney Diseases, said at the American Diabetes Association annual meeting. "Overall, more than 40% of diabetics in the study population had some degree of hearing loss."
Dr Cowie reported data in 5140 individuals (aged 20-69 years) who underwent an audiometric examination between 1999 and 2004 as part of NHANES and who also completed a diabetes questionnaire. Overall, 399 participants reported a diagnosis of diabetes, and 4741 said they did not have the disease.
"While the pathologic changes that accompany diabetes could plausibly affect the vasculature or the neural system of the inner ear, which would lead to sensorineural hearing impairment, epidemiological evidence to date has suggested only a modest association," Dr Cowie noted.
In the NHANES study, pure-tone air conduction hearing thresholds in decibels were obtained for each ear at 500, 1000, 2000, and 4000 Hz.
Participants were considered hearing impaired if their pure-tone average of the threshold frequencies was >25 dB in 1 or both ears.
After adjusting for age, 31.6% of patients with self-reported diabeteshad hearing impairment at the lower frequencies compared with 14.5% of the nondiabetics.
Neither age, gender, race/ethnicity, education, income-to-poverty ratio, nor leisure-time noise exposure was responsible for the association between diabetes and hearing impairment.
Dr Cowie pointed out that the biologic mechanism for the association between diabetes and hearing impairment has not been identified, despite her belief that it may be vascularor neurologic.
As for screening, early is better, she said. "Many newly diagnosed diabetics have actually had undiagnosed diabetes for a long time. And, in fact, in many type 2 patients, their disease is only diagnosed once a complication brings them to their doctor. So, it would be good to test them for hearing loss, especially if it is found that uncontrolled glucose levels may contribute to hearing loss."