Diabetes What it is

Diabetes mellitus is a common condition characterized by high blood glucose (sugar) levels. This condition occurs when the pancreas produces insufficient amounts of the hormone insulin, or the body's tissues become resistant to normal or even high levels of insulin, or a combination of both of these problems. Diabetes is a chronic medical condition requiring regular monitoring and treatment. Treatment can effectively control blood glucose levels and minimize a person's risk for the complications of diabetes. Lifestyle adjustments and self-care also play a large role in the treatment of diabetes over time. TYPES OF DIABETES – In the past, several different systems were used to classify the different types of diabetes. Today, diabetes is classified as either type 1 or type 2 diabetes. Type 1 diabetes – Type 1 diabetes usually begins in childhood or young adulthood, but can occur at any age. This type of diabetes occurs when the pancreas produces very little insulin or no insulin at all. People with type 1 diabetes have to take insulin regularly, and if they do not, they develop a serious condition called diabetic ketoacidosis. Type 2 diabetes – Type 2 diabetes begins in adolescence or adulthood. This type of diabetes occurs when the body's tissues respond poorly to normal or even high levels of insulin (called insulin resistance). In addition to insulin resistance, the pancreas produces insufficient amounts of insulin. Insulin treatment may not be necessary, and patients rarely develop diabetic ketoacidosis. However, people with type 2 diabetes often need to take oral medications and follow special diets to lower their blood glucose levels. Diabetes with features of both type 1 and type 2 diabetes – Occasionally, it is difficult to determine the type of diabetes because a person has manifestations of both type 1 and type 2 diabetes. For example, some people with type 2 diabetes develop diabetic ketoacidosis and have an absolute requirement for insulin. Unusual patterns of diabetes appear to be more common in black people. Gestational diabetes – Gestational diabetes refers to diabetes that develops during pregnancy.. Impaired glucose tolerance – Impaired glucose tolerance (sometimes called impaired fasting glucose) is characterized by borderline elevations of blood glucose. Many people with impaired glucose tolerance eventually develop type 2 diabetes, and people with this condition have an increased risk for cardiovascular disease even if they do not develop diabetes. Impaired glucose tolerance is very common: about 11 percent of all people between the ages of 20 and 74 years have impaired glucose tolerance. CAUSES OF DIABETES – A wide range of different factors can cause diabetes. Type 1 diabetes – Type 1 diabetes most often occurs when the person's own immune system destroys the insulin-producing cells of the pancreas. This is called an autoimmune disease and can be detected by finding antibodies directed against the pancreas. When these antibodies are present, it is called type 1A diabetes. Sometimes, despite evidence of pancreatic damage, blood tests do not reveal the presence of antibodies; in this case, the condition is called type 1B diabetes. Type 2 diabetes – Type 2 diabetes results from a complex interaction of predisposing genetic factors and environmental factors. Genetic conditions that affect insulin-producing cells – About 2 to 4 percent of people with type 2 diabetes have an unusual, inherited form of diabetes caused by specific genetic defects that impair the function of insulin-producing cells in the pancreas. Genetic conditions that affect insulin action – Rarely, diabetes is caused by genetic defects that block the binding of insulin to tissues or that alter the physical structure of insulin. Both of these defects interfere with the normal action of insulin. Other conditions of the pancreas – Any condition that damages the pancreas or requires surgical removal of part of the pancreas can cause diabetes. These conditions include cystic fibrosis, hemochromatosis, and pancreatitis (inflammation of the pancreas). Endocrine conditions – Hormone levels in the body are carefully balanced, and several endocrine disorders can indirectly alter the production and action of insulin and lead to diabetes. They include Cushing's syndrome, acromegaly, pheochromocytoma, and hyperthyroidism. Exposure to drugs and chemicals – Certain drugs and chemicals can alter the production and action of insulin, and trigger diabetes. These drugs include beta blockers (which are used to treat hypertension and cardiovascular disease), steroids, and protease inhibitors (which are used to treat human immunodeficiency virus [HIV] infection). Viral infection – Infection with certain viruses may damage the pancreas and cause diabetes. Pregnancy – About 2 percent of pregnant women develop gestational diabetes. This type of diabetes results from the combined effects of placental hormones and the increased dietary intake during pregnancy. SYMPTOMS OF DIABETES – Some people with diabetes have symptoms of high blood glucose levels, including excessive thirst, consumption of large quantities of liquids, excretion of large quantities of urine, weight loss, and blurred vision. However, many people with diabetes have no symptoms at all. DIAGNOSIS OF DIABETES – The diagnosis of diabetes is based on the symptoms noted during a medical history and physical examination and on the results of laboratory tests. Medical history and physical examination – Because heredity plays a role in diabetes, your doctor will ask if any family members have diabetes or conditions commonly associated with diabetes, such as hypertension, high blood lipid levels, and obesity. Although a person may have symptoms of diabetes, a physical examination often reveals few signs of high blood glucose levels early in the course of diabetes. Laboratory tests for diabetes – Several simple blood tests are used to diagnose impaired glucose tolerance and diabetes. Additional tests can determine the type of diabetes and its severity. Random blood glucose test – Blood glucose can be measured at any time throughout the day, regardless of when a person last ate. A random blood glucose level of 200 mg/dL or higher suggests the presence of diabetes. Fasting blood glucose test – Measurement of blood glucose test after a person has fasted for 8 to 12 hours (usually overnight) is the most accurate test for diagnosing diabetes. A level of less than 110 mg/dL is considered normal. A level between 111 and 125 mg/dL suggests that a person has impaired fasting glucose, which is very similar to impaired glucose tolerance. A level of 126 mg/dL or higher suggests that a person has diabetes. Oral glucose tolerance test – In the past, the oral glucose tolerance test was used to diagnose diabetes. Today, this test is rarely used clinically, except to diagnose the diabetes associated with pregnancy (gestational diabetes). During an oral glucose tolerance test, a person is asked to drink a glucose solution, and blood glucose is measured hourly for several hours. A blood glucose level of 200 mg/dL (11.1 mmol/L) or higher 2 hours after drinking the solution suggests that a person has diabetes. Tests for antibodies – In most people with type 1 diabetes, blood tests reveal the presence of antibodies that target the insulin-producing of the pancreas; these antibodies are called islet-cell antibodies. Blood tests may also reveal antibodies directed against glutamic acid decarboxylase, insulin itself, or against insulin receptors. Hemoglobin A1c test – The hemoglobin A1c blood test is not used alone to diagnose diabetes or impaired glucose tolerance. However, this test may provide more information in people with borderline fasting blood glucose values. Normal values for hemoglobin A1c are usually 6 percent or lower. This test is most useful for monitoring blood glucose in people with known diabetes. PREDICTORS OF TYPE 2 DIABETES – Certain factors are helpful for identifying people who are likely to develop type 2 diabetes, although some people with these risk factors never develop diabetes. Impaired glucose tolerance – People with impaired glucose tolerance have an increased risk of type 2 diabetes and an increased risk of cardiovascular diseases such as coronary artery disease. The likelihood of progression from impaired glucose tolerance to type 2 diabetes is greater in certain ethnic groups; for example, Hispanic people more than white people . Obesity also increases the likelihood that a person with impaired glucose tolerance will develop type 2 diabetes. Results of laboratory tests – The results of the oral glucose tolerance test and the hemoglobin A1c test help predict the likelihood that a person will develop type 2 diabetes. In a group of nondiabetic people with risk factors for type 2 diabetes, diabetes later developed in 38 percent of those with an abnormal oral glucose tolerance test, 50 percent of those with an abnormal hemoglobin A1c test, and 69 percent of those with abnormal results on both tests. Obesity – For people of all ages, the risk of developing impaired glucose tolerance or type 2 diabetes increases with increasing body weight, which makes the body's tissues less responsive to insulin. Conversely, weight loss decreases the risk of type 2 diabetes in obese people, and weight loss can improve blood glucose control in people who already have type 2 diabetes. Two additional aspects of obesity have also been linked to the risk of diabetes: the pattern of body fat distribution and birth weight. Body fat distribution – Obese people who have fat distributed in their upper body or abdomen have the greatest risk for type 2 diabetes. Fat distribution is determined by calculating the waist-to-hip ratio. Obese men with a ratio greater than 0.95 and obese women with a ratio greater than 0.85 have the greatest risk for type 2 diabetes. Birth weight – For unknown reasons, low weight at birth is associated with an increased risk for type 2 diabetes later in life. This association is particularly strong in people with a low birth weight who become overweight in middle age. Gestational diabetes – Women who develop gestational diabetes have an increased risk of developing type 2 diabetes. The results of an oral glucose tolerance test 4 to 16 weeks after delivery help predict the risk over the subsequent 5 years. In one study of women who developed gestational diabetes, 84 percent of women with an abnormal test result (impaired glucose tolerance) developed type 2 diabetes, compared with 12 percent of women with a normal test result. Polycystic ovary syndrome – Polycystic ovary syndrome is characterized by irregular menstrual cycles with acne or excessive facial hair growth. Women with this syndrome are at increased risk of both impaired glucose tolerance and type 2 diabetes. Therefore, all women with this syndrome should be evalauated for diabetes. PREDICTORS OF TYPE 1 DIABETES – Type 1 diabetes occurs in genetically susceptible subjects and is probably triggered by one or more environmental agents. It usually progresses over many months or years. Genetic markers can be used to predict the risk of type 1 diabetes in close relatives of a patient with type 1 diabetes. Several antibodies can be detected in blood before the onset of type 1 diabetes. Three are clinically useful: islet-cell antibodies, insulin autoantibodies, and antibodies to glutamic acid decarboxylase. PREDICTORS OF LATE-ONSET TYPE 1 DIABETES – About 7.5 to 10 percent of adults initially diagnosed with type 2 diabetes later have evidence of type 1 diabetes, including islet-cell antibodies or antibodies to glutamic acid decarboxylase and a poor response to treatments that usually control type 2 diabetes. This type of diabetes is called late-onset type 1 diabetes. PREVENTION OF TYPE 2 DIABETES – Three strategies may prevent type 2 diabetes: exercise, weight loss, and drug therapy. Exercise – Regular exercise can decrease a person's risk for developing type 2 diabetes and can improve glucose tolerance in people with impaired glucose tolerance. In one study, a large group of healthy men was followed for 10 years; the men who exercised regularly were much less likely to develop type 2 diabetes over time, and this benefit was especially apparent in obese men who exercised. In another study, a group of men with impaired glucose tolerance was followed for 5 years; 76 percent of the men who exercised regularly had improved glucose tolerance, whereas glucose tolerance worsened in 67 percent of men who did not exercise. Furthermore, type 2 diabetes developed in only 11 percent of the men who exercised but in 29 percent of the men who did not exercise. The Diabetes Prevention Program has reported preliminary results from a trial of 3234 obese individuals with impaired glucose tolerance ("pre-diabetes"). The subjects who were assigned to intensive lifestyle changes (diet and exercise) were less apt to develop type 2 diabetes than those who were assigned to receive medication (metformin). Thus, diet and exercise are extremely important for the prevention of type 2 diabetes. Weight loss – In people with type 2 diabetes, sustained weight loss can improve glycemic control. In those with impaired glucose tolerance, sustained weight loss can improve glucose tolerance and prevent progression to type 2 diabetes. Drug therapy – Three groups of drugs are being evaluated to see if they may prevent type 2 diabetes or slow the progression from impaired glucose tolerance to type 2 diabetes. Metformin – Metformin makes tissues more responsive to insulin. In a study in men with risk factors for type 2 diabetes, metformin was more effective than placebo in promoting weight loss and reducing fasting blood glucose levels. This drug is being tested in a large trial in the United States (called the Diabetes Prevention Program, or DPP). Thiazolidinediones – Rosiglitazone and pioglitazone are thiazolidinedione drugs that increase muscle sensitivity to insulin, improve insulin secretion, and help normalize glucose tolerance in people with impaired glucose tolerance; these findings suggest that this class of drugs may stop or slow the progression to type 2 diabetes. Troglitazone, another drug in this class, was included in the DPP but was withdrawn because of concerns about its safety. Angiotensin-converting enzyme (ACE) inhibitors – ACE inhibitors are most often used to treat cardiovascular disease. However, a large study in people with cardiovascular disease suggested that these drugs may also protect people against type 2 diabetes. In this study, diabetes developed in 3.6 percent of people taking an ACE inhibitor and in 5.4 percent of those taking a placebo. PREVENTION OF TYPE 1 DIABETES – Methods to prevent type 1 diabetes are still in the investigational stage. Several drugs, including azathioprine, cyclosporine, nicotinamide, and insulin, have been given alone or in combination, to decrease the immune-mediated destruction of insulin-producing cells that occurs in type 1 diabetes with modest and usually temporary benefit. Much further research is needed before these methods can be used in the greater population at risk for type 1 diabetes. A large trial in the United States (called the Diabetes Prevention Trial for type 1 diabetes, or DPT-1) is testing the use of insulin (either by mouth or as an injection) in the close relatives of people with type 1 diabetes.