Diabetes mellitus is a metabolic disorder with abnormally high blood glucose levels (hyperglycemia) as its most prominent feature. During intestinal digestion, carbohydrates and proteins are broken down into simple sugars and amino acids, respectively. The liver converts all of the sugars and some of the amino acids into glucose, a simple sugar that is used for energy by every cell in the body. Glucose passes from the bloodstream into the cells with the help of insulin, a hormone produced by the pancreas (a pear-shaped organ located just below the stomach). By attaching to receptor sites on the surface membrane of a cell, insulin promotes the movement of glucose-transport proteins from the interior of the cell to its surface, where they bind with glucose and carry it into the cell. In diabetes mellitus, several problems may interfere with this process: pancreatic insulin production may be partially or completely impaired, or body cells may become unable to use normal amounts of insulin efficiently.
These underlying problems in fact distinguish the two main types of the diabetes. In type 1, or insulin-dependent diabetes mellitus (IDDM), also known as juvenile diabetes, the pancreas produces little or no insulin. Type 1 diabetes develops suddenly and most commonly affects those under age 30; the average age of onset is between 12 and 14. However, IDDM accounts for only 7 to 10 percent of cases of diabetes mellitus. In the much more common type 2, or non-insulin-dependent diabetes mellitus (NIDDM), also known as adult-onset diabetes, insulin production by the pancreas is normal or only slightly reduced, but cells are unable to respond efficiently to insulin-a condition referred to as insulin resistance. The onset of type 2 diabetes is usually gradual and tends to affect people over age 40, particularly those who are overweight. Infrequently, an adult may develop type 1 diabetes.
In both type 1 and type 2 diabetes, the hyperglycemia leads to excretion of glucose in the urine and an accompanying increase in urine production. If inadequate amounts of insulin are administered to patients with type 1 diabetes, unrestrained release of fatty acids from adipose (fat) tissue leads to the overproduction of ketone bodies in the liver. Accumulation of ketone bodies can cause a life-threatening condition known as diabetic ketoacidosis (DKA). DKA may occasionally affect those with type 2 diabetes in periods when the body is highly stressed, for example, during a severe infection.
People with type 2 diabetes are susceptible to another life-threatening condition known as a hyperosmolar nonketotic state, characterized by extremely high blood sugar levels. This condition usually occurs in elderly persons with some other serious underlying illness. An episode of either DKA or the hyperosmolar state may be the first indication that someone has diabetes.
People with diabetes may also suffer from low blood sugar (hypoglycemia) if too much insulin or oral hypoglycemic agent is given for treatment (see Hypoglycemia for more information).
After 10 to 20 years of diabetes, patients are likely to develop complications, such as vision disorders, kidney damage, and peripheral nerve degeneration (neuropathy). Strict control of blood glucose can delay or prevent these complications. Loss of sensation in the feet may allow injuries to go unchecked and become infected. In addition, people with diabetes are at increased risk for developing narrowing of the coronary arteries (see Coronary Artery Disease for more information) as well as narrowing of arteries supplying the brain and legs. The combination of foot infections and decreased blood supply can lead to gangrene (tissue death), which may require amputation. Diabetes mellitus (and its complications) is the fourth leading cause of death in the United States.
Treatment of type 1 diabetes requires between one and four daily injections of insulin. (Insulin cannot be taken orally, since digestive juices would destroy it.) In addition, diet and exercise must be carefully planned to ensure that blood glucose levels are neither too high nor too low. Type 2 diabetes may be controlled with a combination of diet, exercise, and weight loss, although medications (including insulin) are often necessary. Treatment is largely a process of self-management. Although there is no cure, almost all people with diabetes are able to control their symptoms and lead full, productive lives.
