The Center of Disease Control and Prevention (CDC) defines diabetes as, “a chronic (long-lasting) health condition that affects how your body turns food into energy.”4 After consuming food, the body breaks it down and turns it into sugar that gets released into the bloodstream. When blood sugar increases, a signal is sent to the pancreas to release insulin into the bloodstream. Insulin allows the body to absorb the blood sugar to use as energy. When there is dysfunction related to insulin production or absorption, a person may have diabetes.
There are two main types of diabetes: Type 1 and Type 2. Type 1 diabetes is typically diagnosed at an early age. According to the CDC, Type 1 diabetes is considered an autoimmune condition that does not allow the pancreas to produce insulin.4 When the body does not produce insulin, blood sugar increases to dangerous levels because the body cannot use the sugar as energy. Patients with Type 1 diabetes will need to take insulin every day in order to survive. There is no cure or known prevention methods for Type 1 diabetes. In patients with Type 2 diabetes, the pancreas produces insulin but the body does not use it properly, causing an increase in blood sugar. Type 2 diabetes can be delayed or even prevented by adopting a healthy lifestyle. This includes eating healthy food, losing weight, and incorporating exercise into one’s life. Type 2 diabetes is typically manageable with a healthy diet and exercise, but some may also need to take medication or insulin.
According to the American Diabetes Association, over 37 million people in the United States have diabetes, with 90%-95% of cases being Type 2.2 Untreated diabetes can lead to serious health concerns, such as kidney disease, vision loss, heart disease, and even hearing loss.
The Diabetes and Hearing Loss Connection
The auditory system has three main components: the outer ear, the middle ear, and the inner ear. The outer ear includes the pinna, cartilaginous structure on the side of the head, and the outer ear canal. The middle ear is composed of the tympanic membrane, also known as the eardrum, and the ossicular chain, or the three bones behind the tympanic membrane. Those three bones (the malleus, the incus, and the stapes) are the smallest bones in the human body. The inner ear is composed of the cochlea, the organ of hearing. The cochlea is a small snail shell shaped structure that includes hundreds of thousands of “hair cells” that send signals to the brain.
The pinna funnels sound waves into the ear canal. Those sound waves travel down to the eardrum, which causes the eardrum to vibrate. The fluid in the inner ear moves with the vibrations from the ossicular chain, stimulating the hair cells, which then send the signals to the brain through the auditory nerve.
According to the American Diabetes Association, hearing loss is twice as common in individuals with diabetes when compared to those without diabetes.1 There are several correlations between diabetes and hearing loss: hyperglycemia, cardiovascular disease, medications that treat diabetic comorbidities, and more.
Hyperglycemia, or an abnormally high level of sugar in the bloodstream, is common in untreated diabetes. Chronic hyperglycemia can lead to nerve damage throughout a person’s body, and can cause damage to organs in the body that consume high levels of energy, including kidneys and the inner ear. A portion of the inner ear called the stria vascularis is particularly impacted by hyperglycemia. The stria vascularis is responsible for creating and maintaining a fluid called endolymph in the inner ear.7 When this structure is damaged by hyperglycemia, signals are unable to be sent throughout the remainder of the auditory system.
Patients with a history of Type 2 diabetes often have secondary cardiovascular disease. Within the auditory system, there is a complex network of capillaries and other vascular microstructures. Oxygenated blood is essential to the function of the auditory system, particularly within the inner ear. Postmortem histological studies in patients with cardiovascular disease secondary to diabetes have shown a thickening of the vascular walls in structures of the inner ear.7 If blood is unable to properly circulate through the inner ear, it may result in “anoxia,” or a lack of oxygen, to the structures. When anoxia occurs in the inner ear, the histologic studies indicate significant damage to the hair cells.
The individuals suffering from cardiovascular disease secondary to Type 2 diabetes are often prescribed aspirin to assist with blood flow and to prevent blood clots. Aspirin is one of several medications known to be “ototoxic,” or toxic to the ears. Ototoxic medications can lead to hearing loss by causing the death of hair cells within the inner ear. Hearing loss caused by ototoxicity is most commonly seen in higher frequencies.
Individuals with Type 2 diabetes are at a higher risk for developing different types of cancer than those without Type 2 diabetes. According to one meta-analysis, a person with Type 2 diabetes is two times more likely to develop liver, pancreas, and endometrial cancers than those without Type 2 diabetes. Additionally, those patients are at a one and one half times higher risk for developing colon, rectum, breast, and bladder cancers. Of patients diagnosed with cancer, 8%-18% also have diabetes.7 Many types of chemotherapies used to treat cancer, such as cisplatin, are known to be ototoxic. Patients undergoing chemotherapy should be closely followed by an audiologist and an oncologist for ototoxicity monitoring before and after the administration of ototoxic drugs.
Other ototoxic medications can include antibiotics. Diabetes puts a patient at a higher risk for developing bacterial and fungal infections, which often require the administration of antibiotics. Many aminoglycoside antibiotics, such as tobramycin, gentamicin, and amikacin, are known to be ototoxic.7 Similar to ototoxic chemotherapies, aminoglycoside antibiotics cause damage to the inner ear, leading to hair cell death.
Signs of Hearing Loss
According to the National Institute on Deafness and Other Communication Disorders, over 37 million Americans 18 years and over report some kind of difficulty with listening, and over 28 million American adults could benefit from wearing hearing aids.6 There are different signs that a person may have hearing loss, and many of them are subtle. A person with hearing loss may ask their conversation partners to repeat themselves frequently. They may also experience difficulty listening in crowds or in background noise.3 A person with hearing loss may feel as if they are unable to contribute to conversations, and they may socially isolate themselves.
Good Diabetes Care is Key
As diabetes is a complex diagnosis involving many different bodily structures, patients with diabetes should have a number of professionals involved with the management of care. An example of a multidisciplinary management team includes the following: primary care physician, endocrinologist, cardiologist, opthamologist, psychologist, diabetic educator, audiologist, and speech language pathologist.
Proper management is essential for patients with either Type 1 or Type 2 diabetes. Maintaining a healthy lifestyle may decrease the likelihood of developing secondary comorbidities to diabetes.
Of the 37 million Americans with diabetes,2 and the 28 million American adults who could benefit from amplification,6 the populations often overlap. If an individual thinks that they may have a hearing loss, it is important to have a comprehensive evaluation completed to assess hearing status. Hearing loss can lead to social isolation, as a person may feel as if they can no longer contribute to conversations. This may decrease a person’s quality of life. A comprehensive audiometric evaluation can determine whether or not a person is a candidate for amplification. Treating hearing loss with hearing aids, cochlear implants, and assistive listening devices can significantly improve a person’s quality of life by allowing them to communicate with others. Living with diabetes or hearing loss can be difficult, but they are both manageable conditions.
1American Diabetes Association. (2022). Diabetes complications: Diabetes and hearing loss. American Diabetes Association. https://diabetes.org/diabetes/diabetes-and-hearing-loss
2American Diabetes Association. (2022). Diabetes overview. American Diabetes Association. https://diabetes.org/diabetes
3Center for Disease Control. (2022, May 27). Diabetes and hearing loss. Center for Disease Control and Prevention. https://www.cdc.gov/diabetes/managing/diabetes-hearing-loss.html
4Center for Disease Control. (2022, July 7). What is diabetes? Center for Disease Control and Prevention. https://www.cdc.gov/diabetes/basics/diabetes.html
5Enock, M. (2015). Hearing Loss and Diabetes. American Speech Language Hearing Association. https://www.asha.org/articles/hearing-loss-and-diabetes/
6National Institute on Deafness and Other Communication Disorders. (2015). Quick statistics. Retrieved from www.nidcd.nih.gov/health/statistics/Pages/quick.aspx.
7Samocha-Bonnet, D., Wu, B., & Ryugo, D. (2021). Diabetes mellitus and hearing loss: A review. Aging Research Reviews, 71.