diabetes or diabetes mellitus (məlī´təs), chronic disorder of glucose (sugar) metabolism caused by inadequate production or use of insulin, a hormone produced in specialized cells (beta cells in the islets of Langerhans) in the pancreas that allows the body to use and store glucose. It is a leading cause of death in the United States and is especially prevalent among African Americans. The treatment of diabetes was revolutionized when F. G. Banting and C. H. Best isolated insulin in 1921.
The lack of insulin results in an inability to metabolize glucose, and the capacity to store glycogen (a form of glucose) in the liver and the active transport of glucose across cell membranes are impaired. The symptoms are elevated sugar levels in the urine and blood, increased urination, thirst, hunger, weakness, weight loss, and itching. Prolonged hyperglycemia (excess blood glucose) leads to increased protein and fat catabolism, a condition that can cause premature vascular degeneration and atherosclerosis (see arteriosclerosis). Uncontrolled diabetes leads to diabetic acidosis, in which ketones build up in the blood. Patients have sweet-smelling breath, and may suffer confusion, unconsciousness, and death. There are two distinct types of diabetes mellitus: insulin-dependent and noninsulin-dependent.
Insulin-dependent diabetes (Type I), also called juvenile-onset diabetes, is the more serious form of the disease; about 10% of diabetics have this form. It is caused by destruction of pancreatic cells that make insulin and usually develops before age 30. Type I diabetics have a genetic predisposition to the disease. There is some evidence that it is triggered by a virus that changes the pancreatic cells in a way that prompts the immune system to attack them. The symptoms are the same as in the non-insulin-dependent variant, but they develop more rapidly and with more severity. Treatment includes a diet limited in carbohydrates and saturated fat, exercise to burn glucose, and regular insulin injections, sometimes administered via a portable insulin pump. Transplantation of islet cells has also proved somewhat successful since 1999, after new transplant procedures were developed, but the number of pancreases available for extraction of the islet cells is far smaller than the number of Type I diabetics. Patients receiving a transplant must take immunosuppressive drugs to prevent rejection of the cells, and many ultimately need to resume insulin injections, but despite that transplants provide real benefits for some whose diabetes has become difficult to control.
Noninsulin-dependent diabetes (Type 2), also called adult-onset diabetes, results from the inability of the cells in the body to respond to insulin. About 90% of diabetics have this form, which is more prevalent in minorities and usually occurs after age 40. Although the cause is not completely understood, there is a genetic factor and 90% of those affected are obese. As in Type I diabetes, treatment includes exercise and weight loss and a diet low in total carbohydrates and saturated fat. Some individuals require insulin injections; many rely on oral drugs, such as sulphonylureas, metformin, acarbose or another alpha-glucosidase inhibitor, thiazolidinediones, or dipeptidyl peptidase–4 (DPP-4) inhibitors.
Diabetes affects the way the body handles fats, leading to fat accumulation in the arteries and potential damage to the kidneys, eyes, heart, and brain, and statins (cholesterol-lowering drugs) may be prescribed to prevent heart disease. It is the leading cause of kidney disease. Many patients require dialysis or kidney transplants (see transplantation, medical). Most cases of acquired blindness in the United States are caused by diabetes. Diabetes can also affect the nerves, causing numbness or pain in the face and extremities. A complication of insulin therapy is insulin shock, a hypoglycemic condition that results from an oversupply of insulin in relation to the glucose level in the blood (see hyperinsulinism).
See A. Bloom, Diabetes Explained (1973); Portland Area Diabetes Program, Diabetes and Insulin (1988); M. Davidson, Diabetes Mellitus: Diagnosis and Treatment (1991).