Diabetes is a long-term disease that disrupts the body’s ability to use a sugar called glucose. The formal medical term for the disease is diabetes mellitus << DY uh BEE tihs, or DY uh BEE teez, MEHL uh tuhs >>. Glucose is a product of carbohydrate digestion. It circulates in the blood to the body’s cells, where it serves as one of the chief sources of energy.
Diabetes leads to a high concentration of glucose in the blood, a condition called hyperglycemia. Persisting over many years, hyperglycemia injures small blood vessels in the eye, kidneys, and nervous system. It can lead to blindness, kidney failure, and nerve damage. Hyperglycemia also damages larger blood vessels, and patients with diabetes have a greater risk of heart attack, stroke, and heart failure. Patients also have an increased risk of developing Alzheimer’s disease later in life.
Causes.
The two principal types of diabetes are called Type 1 and Type 2. Both forms are characterized by abnormalities in the production and use of a hormone called insulin. This hormone helps bring glucose from the bloodstream into cells, chiefly the cells of the muscles, body fat, and liver. Low insulin levels reduce the body’s ability to take up glucose from the blood. They also cause increased production of glucose by the liver. Both of these processes lead to hyperglycemia.
Type 1 diabetes,
also called insulin-dependent diabetes, results from the destruction of insulin-producing cells in the pancreas, an organ in the abdomen. The insulin-producing cells, called beta cells, are the only cells in the body that can produce insulin. When they are destroyed, the resulting deficiency of insulin causes the level of glucose in the bloodstream to rise.
Physicians consider Type 1 diabetes an autoimmune disease, because the beta cells are destroyed by the body’s own immune system. It typically strikes before the age of 20 and is often called juvenile diabetes. People with Type 1 diabetes require insulin injections several times a day to maintain near normal blood glucose levels and prevent the effects of hyperglycemia.
Type 2 diabetes
is the most common form of the disease. It occurs most often in middle-aged and older individuals. Type 2 diabetes is caused by the combined effects of reduced production of insulin by the beta cells and a decrease in the body’s ability to use insulin, a condition called insulin resistance.
Scientists do not fully understand how Type 2 diabetes develops, but they have identified several factors that increase a person’s risk for developing the disease. Obesity (excess body weight) and a lack of exercise are among the most important risk factors. Lifestyles that include eating larger portions of high-calorie food combined with less physical activity are now common in much of the industrialized world. As a result, the incidence of Type 2 diabetes has increased dramatically.
Some people and ethnic groups have a genetic tendency to develop Type 2 diabetes. In the United States, Type 2 diabetes is more common among American Indians, Hispanic Americans, and African Americans.
Symptoms
of diabetes include changes in vision, dry skin, weight loss, a reduced ability to resist infection, frequent urination, and thirst. All of these symptoms are due to hyperglycemia.
In Type 1 diabetes, symptoms may occur suddenly and severely. When cells cannot use glucose because of the severe lack of insulin in Type 1 diabetes, they begin to break down stored fat for energy. Meanwhile, blood glucose levels continue to rise. The breakdown of fat produces chemical by-products called ketones. The build-up of ketones in the blood, a condition called ketoacidosis << `kee` toh `a` suh DOH sihs >>, can lead to nausea, vomiting, and loss of consciousness. Type 1 diabetes is fatal unless treatment replaces the missing insulin.
In Type 2 diabetes, symptoms may develop over months or years and often go unrecognized. In most cases, blood sugar levels rise gradually and ketoacidosis generally does not occur. But hyperglycemia slowly damages organs throughout the body.
Insulin resistance that can progress to diabetes often accompanies pregnancy. Such gestational diabetes requires careful monitoring and treatment to protect the health of the mother and child. Gestational diabetes usually disappears after the mother gives birth. Scientists have also found that the use of some drugs, such as corticosteroids, can cause diabetes in some people.
Treatment.
There is currently no cure for diabetes. However, once diabetes is diagnosed, there are many ways to lower the blood glucose and prevent complications of the disease. Treatment programs usually involve a diet designed to meet a patient’s individual needs and an exercise program. Patients also must monitor their own blood glucose levels several times a day, using portable monitoring devices that measure glucose levels from a single drop of blood.
Patients with Type 1 diabetes and some with Type 2 diabetes require insulin. These patients inject the hormone under their skin, because insulin is broken down by digestion if it is taken by mouth. Drug manufacturers have developed various rapid, intermediate, and long-lasting preparations of insulin that allow patients to simulate the normal pattern of insulin production that occurs in healthy individuals.
Some patients use an external insulin pump, which administers insulin beneath the skin according to a programmed schedule. Scientists are currently working to develop an insulin infusion pump that both monitors blood sugar and delivers an appropriate dose of insulin to maintain blood glucose at normal levels. These devices allow patients with diabetes to better control their disease and reduce complications.
Treatments for Type 2 diabetes aim at reducing the body’s resistance to insulin. Strategies include losing weight, controlling diet, and exercising regularly. Some patients may use insulin or take medications that stimulate their own insulin-producing cells to make more. Other medications reduce insulin resistance, lower glucose production by the liver, or reduce the amount of glucose absorbed during digestion. Many patients achieve the best control of their blood glucose with a combination of treatments.
Patients with diabetes who take insulin or other medications to reduce blood glucose occasionally risk developing a complication called hypoglycemia. This condition occurs when high levels of insulin cause blood glucose levels to drop to a dangerous level. Symptoms of hypoglycemia include confusion, loss of consciousness, rapid heartbeat, sweating, shakiness, and seizure.
Research.
Scientists are investigating the autoimmune process that causes Type 1 diabetes in an effort to develop methods for preventing or curing this disease. Scientists are also researching the use of islet transplants. Islets are small clusters of pancreatic cells that include beta cells. In this procedure, physicians isolate islets from a donor’s pancreas. The islets are then injected into the patient through a vein inside the abdomen and settle in the liver, where they begin producing insulin. Limitations on the availability of donor organs has led other scientists to investigate the use of stem cells to cure diabetes. Stem cells can develop into any kind of cell in the body. Scientists think that stem cells may be able to replace the destroyed beta cells in patients with Type 1 diabetes, curing them.
Diabetes insipidus
is a rare disorder that is unrelated to Type 1 or Type 2 diabetes except by name. In this disorder, the kidneys produce large amounts of urine, causing severe dehydration. The disorder is caused either by a lack of antidiuretic hormone (also called ADH or vasopressin), or by the failure of the kidneys to respond to the hormone. In either case, the kidney cannot retain water normally and produces large amounts of dilute urine.
See also Banting, Sir Frederick Grant; Hypoglycemia; Insulin; Obesity; Peripheral artery disease (PAD).
