The preliminary findings of a new study have determined that diabetes, which is approaching epidemic proportions, may lead to premature aging of the auditory system. These results add to the literature chronicling the damaging impact of the disease on various organs of the body, including the kidneys, eyes, heart and nervous system.
Diabetes mellitus affects at least 16 million Americans, ranks seventh as a cause of death in the United States, and costs the national economy more than $100 billion yearly. Approximately 95 percent of people with diabetes have type 2, in which the pancreatic beta cells retain some insulin-producing potential. The rest have type 1 and require insulin for long-term survival.
The findings come from the Department of Veterans Affairs National Center for Rehabilitative Auditory Research (NCRAR), which is conducting a five-year epidemiological study to assess the prevalence and severity of auditory dysfunction in veterans with diabetes. It is the largest prospective study of diabetes and auditory function to date.
Study author Nancy Vaughan, PhD, and NCRAR director Stephen Fausti, PhD, presented the preliminary results of the study last month at the Mid Winter Meeting of the Association for Research in Otolaryngology in Daytona Beach, FL.
A total of 694 veterans, ages 25-85, participated, including 342 with diabetes and 352 control subjects. Participants were divided into two groups: people age 60 and under and those over 60.
All of the subjects completed audiometric testing, including otoacoustic emissions (OAEs) and auditory brainstem response (ABR), and a questionnaire. Glucose levels and HbA1c, a measure of overall diabetes control, were assessed; and cooling and vibration sensitivity were measured as indicators of peripheral neuropathy.
Interim results were analyzed in relation to duration of disease, age, self-reported noise exposure, insulin use and hemoglobin. Data also were collected on microvascular and neuropathy changes typically associated with diabetes. Further analysis is needed to determine the role of these diabetic mechanisms in the outcomes of this study.
Significant findings to date are as follows:
- increased hearing loss in veterans with diabetes age 60 and younger, compared to those of the same age without diabetes;
- a lack of effect on the cochlear amplifier system as shown by OAE testing; and
- delays in central auditory processing revealed in ABR tests.
Further investigation is planned to determine the cause and effect of the central auditory processing delays (CAPD) seen in patients with diabetes.
Patients with diabetes under age 60 exhibited greater hearing loss than control subjects of the same age. This finding is consistent with the theory that diabetes is associated with accelerated aging of the auditory system.
Hearing loss in those over 60 was similar between those with and without diabetes. Presbycusis may obscure any changes in hearing due to diabetes in the older patients with diabetes, the researchers theorized.
Central auditory processing functions are affected by diabetes to a greater extent than peripheral functions, such as hearing loss, indicating that ABR and pure tone testing may be appropriate to reveal changes early in diabetic care. Since hearing takes place not only in the ear but in higher auditory and cognitive centers responsible for processing the sounds received in the cochlea, early identification of processing changes could be important to verbal communication.