Diabetes and Hearing Loss: Exploring Connections

As printed in Hearing Health, volume 19:3, Fall 2003

By Daniel McDermott, CCC-A, and Nancy Vaughan, Ph.D.

A major health story throughout the last five years has been the almost exponential rise in the incidence of diabetes. Facts and figures about the disease compiled by the Centers for Disease Control and Prevention (CDC) starkly describe this ongoing epidemic. Approximately 17 million Americans have diabetes, a startling figure. But the statistics grow even more alarming; the number of diagnosed adults has increased an astounding 61 percent since 1991 and is projected to more than double by 2050.

Diabetes is now the sixth leading cause of death in the U.S. Potentially fatal complications include stroke, heart disease and kidney failure; blindness is among other severe complications. The prevalence among older Americans is as high as 20 percent, affecting seven million people over the age of 65.

Even with the substantial media coverage that the disease warrants and receives, there is little about a possible relationship between diabetes and hearing loss. It is logical to inquire if there is one for two reasons: 1) each is present in large numbers of older adults and 2) diabetes often damages the eyes, another of the sensory organs.

A possible connection between hearing loss and diabetes has been the subject of studies dating back as far as the 1800s but damage to the body’s hearing system is not as well-documented as with vision. Although the diabetic mechanisms that affect hearing sensitivity remain obscure, recent research showing diabetes-related changes in the auditory systems of animals is spurring interest in more clearly defining the interaction across species and in humans.

On Diabetes
Diabetes is a complex disorder diagnosed when the body is unable to effectively manage the processing of sugar (glucose) in the bloodstream. Although glucose is the main source of fuel for the body’s cells, its levels must be closely regulated. This is the job of insulin, a hormone produced by the pancreas that transports glucose into cells for use as fuel and moves excess sugar from the bloodstream into the liver for storage.

Five to 10 percent of diabetics do not produce insulin at all, a condition classified as type 1 diabetes. Most people with the disease have type 2. People with this type manufacture insulin but their bodies may not make sufficient amounts or proper use of what is produced. In both types, an excessive amount of glucose in the bloodstream, termed hyperglycemia, creates a dangerous environment for cells throughout the body.

The cause of diabetes remains unknown although genetics as well as behavioral factors, such as obesity and lack of exercise, appear to be contributing agents. It is possible, however, to manage diabetes and prevent hyperglycemia in many cases by adhering to strict regimens of carefully planned diets, physical activity and home glucose level monitoring. People with type 1 diabetes and approximately 40 percent of people with type 2 also require insulin injections in order to maintain healthy blood sugar levels.

The stakes of mismanaging or ignoring diabetes are high. Severe complications usually stem from two types of cell damage. Vascular damage commonly occurs in the eyes and kidneys and in many cases extends to the heart. Numbness or tingling in the hands and feet are often the result of neurological damage. Diabetes also affects nerve cells in the brain, causing cognitive deficits, such as difficulty performing rapid mental tasks.

Likely Connections
Since vascular and nerve tissues play predominant roles in auditory function, any disease that has the capacity to damage their cells has potential to negatively affect the various hearing organs. A link between hearing and diabetes seems likely indeed if the rich blood supply to the cochlea and/or the nerve centers in the hearing pathways, including the brain, are affected.

In fact, diabetes-related damage to blood vessels in the cochlea was documented in recent animal studies. Through surgery, researchers observed microvascular changes in the inner ear, including differences in circulation flow, narrowing capillaries and loss of outer hair cells that amplify the sounds that enter the cochlea. Such changes would be nearly impossible to observe directly in human ears. The human auditory system is obscured because the cochlea is embedded in the temporal bone and the neural pathways are complex and distributed through the brainstem and cortex.

We know, however, that similar deleterious processes related to diabetes take place in human eyes and kidneys. It is logical to suspect, therefore, that these changes would also take place in the highly vascularized inner ear.

Further, results of audiometric testing using otoacoustic emissions to indirectly examine outer hair cell function show differences between diabetic and non-diabetic patients even when hearing loss is not present. This suggests that certain hearing structures may be damaged in diabetic patients before the impact can be diagnosed by clinical tests of hearing sensitivity.

Nerve cell damage related to diabetes may affect structures farther along the hearing pathway as well. Comparative results from a study using another objective audiometric test, auditory brainstem response, show that the electrical signals from the cochlea may travel more slowly along the auditory nerve and in the brainstem pathways in diabetic than in non-diabetic people. Alterations in the brain cells in some diabetics also may result in slower processing of complex sounds such as speech.

Simply put, certain individuals with diabetes could have difficulty understanding speech even if they have little or no hearing loss. In addition, if a person loses vision, the problem could be exacerbated since visual cues (e.g., gestures, lip movements, etc.) that
are normally helpful in communication situations are unavailable.

At the present time, experts recommend that people with diabetes undergo regular examinations to monitor changes in vision, kidney function, tactile and thermal sensitivity and cardiovascular health. Continuing research to define the nature of the connection between hearing loss and diabetes may show that specific tests for hearing loss should be included as part of their routine care. We may also learn more about how diabetes affects individuals with pre-existing hearing loss.

Considering, however, the drastic effects diabetes has on vital organs, the addition of hearing loss to the list of potential complications might not make health news headlines. If preventing stroke, heart disease, kidney failure and blindness are not sufficient motivation to change one’s lifestyle to prevent diabetes, hearing loss is not likely to tip the scales.

Evidence of the impact of establishing a connection between hearing loss and diabetes would be a change in the standard of care for diabetics, ensuring that physicians address the potential relationship of diabetes and hearing loss, add monitoring of hearing abilities to their preventive care protocol and refer all patients with a hearing loss, diabetics or not, to a hearing health professional for treatment so they can manage and make the most of their hearing abilities.

Are you at risk for developing diabetes? Find out with this questionnaire. Give yourself the designated points next to each statement that is true for you. If a statement is false, give yourself a zero. Then add your total score.

Scoring 3-9 points
You are probably at low risk for having diabetes now but don’t forget about it. Keep your risk low by losing weight if you are overweight, being active most days and eating low fat meals that are high in fruits, vegetables and whole grain foods.

Scoring 10 or more points
You are at high risk for having diabetes. Only your healthcare provider can test you. See yours soon and find out if you have diabetes.

©2003 American Diabetes Association. Reprinted with permission from the American Diabetes Association.

If you weigh the same or more than the amount listed for your height, you may be at risk for diabetes.

Daniel McDermott, M.A., CCC-A, and Nancy Vaughan, Ph.D., are researchers at the National Center for Rehabilitative Auditory Research at the Veterans Affairs Medical Center in Portland, Oregon. Both are involved with the center’s study of diabetes and hearing.