A worldwide problem among patients with diabetes is the myriad of serious medical complications that often accompany the disease. Most adults with diabetes have cardiovascular disease risk factors such as hypertension and high cholesterol. The risk for adverse cardiovascular outcomes, such as stroke or a fatal cardiac event, is two to four times higher among adults with diabetes than those without. Diabetic retinopathy is the leading cause of blindness in the United States. Among Americans, diabetes is also the leading cause of kidney failure. Severe forms of diabetic nerve disease are a major reason for amputation of lower extremities. Diabetic autonomic neuropathies can affect cardiovascular, gastrointestinal, bladder, and erectile function. Because diabetes is a systemic disease with accompanying pathology affecting multiple organ systems, it is reasonable to inquire whether the auditory system is among those affected.

Diabetes and hearing loss are two of America’s leading health concerns. A study conducted by the National Institutes of Health (NIH) over a four-year period and published last year in the Annals of Internal Medicine, suggests that patients with diabetes are more than twice as likely to have hearing loss as non-diabetics. This means that many of the approximately 23.6 million diabetics in the United States and 285 million worldwide are predisposed to – or may already have – a hearing loss. Also, of the 79 million adults thought to be pre-diabetic, the rate of hearing loss is 30% higher than in those with normal blood sugar.

A 2003 study conducted by Kakarlapudi, Sawyer, and Staecker published in Otology & Neurotology concluded that sensorineural hearing loss was more common in patients with diabetes than in the control nondiabetic patients, and severity of hearing loss seemed to correlate with progression of disease as reflected in serum creatinine. This may have been due to microangiopathic disease or Susac Syndrome of the inner ear.

Diabetes Pathophysiology

An understanding of the pathophysiology of diabetes rests upon knowledge of the basics of carbohydrate metabolism and insulin action (click on the picture for a video). Following the consumption of food, carbohydrates are broken down into glucose molecules in the gut. Glucose is absorbed into the bloodstream elevating blood glucose levels. This rise in glycemia stimulates the secretion of insulin from the beta cells of the pancreas. Insulin is needed by most cells to allow glucose entry. Insulin binds to specific cellular receptors and facilitates entry of glucose into the cell, which uses the glucose for energy. The increased insulin secretion from the pancreas and the subsequent cellular utilization of glucose results in lowered blood glucose levels. Lower glucose levels then lead to decreased insulin secretion.

If insulin production and secretion are altered by disease, blood glucose dynamics will also change. When insulin production is decreased, glucose entry into cells is inhibited, resulting in hyperglycemia. The same effect will be seen if insulin is secreted from the pancreas but is not used properly by target cells. If insulin secretion increases, blood glucose levels may become very low (hypoglycemia), as large amounts of glucose enter tissue cells and little remains in the bloodstream.

Following meals, the amount of glucose available from carbohydrate breakdown often exceeds the cellular need for glucose. Excess glucose is stored in the liver in the form of glycogen, which serves as a ready reservoir for future use. When energy is required, glycogen stores in the liver are converted into glucose via glycogenolysis, elevating blood glucose levels and providing the needed cellular energy source. The liver also produces glucose from fat (fatty acids) and proteins (amino acids) through the process of gluconeogenesis. Glycogenolysis and gluconeogenesis both serve to increase blood glucose levels. Thus, glycemia is controlled by a complex interaction between the gastrointestinal tract, the pancreas, and the liver.

Multiple hormones may affect glycemia. Insulin is the only hormone that lowers blood glucose levels. The counter-regulatory hormones such as glucagon, catecholamines, growth hormone, thyroid hormone, and glucocorticoids all act to increase blood glucose levels, in addition to their other effects. Statistics on diabetes worldwide are as follows:

366 million people have diabetes in 2011; by 2030 this will have risen to 552 million
The number of people with type 2 diabetes is increasing in every country
The greatest number of people with diabetes are between 40 to 59 years of age
183 million people (50%) with diabetes are undiagnosed
Diabetes caused 4.6 million deaths in 2011
Diabetes caused at least $465 billion in healthcare expenditures in 2011; 11% of total healthcare expenditures in adults (20-79 years)
78,000 children develop type 1 diabetes every year