Diabetes explained: What is it? Who gets it?Posted: Updated:
Almost everyone knows someone who has diabetes. An estimated 16 million people in the United States have diabetes mellitus--a serious, lifelong condition. About one-third of these 16 million people have not yet been diagnosed. Each year, about 800,000 people are diagnosed with diabetes.
What Is Diabetes?
Diabetes is a disorder of metabolism--the way our bodies use digested food for growth and energy. Most of the food we eat is broken down into glucose, the form of sugar in the blood. Glucose is the main source of fuel for the body.
After digestion, glucose passes into the bloodstream, where it is used by cells for growth and energy. For glucose to get into cells, insulin must be present. Insulin is a hormone produced by the pancreas, a large gland behind the stomach.
When we eat, the pancreas is supposed to automatically produce the right amount of insulin to move glucose from blood into our cells. In people with diabetes, however, the pancreas either produces little or no insulin, or the cells do not respond appropriately to the insulin that is produced. Glucose builds up in the blood, overflows into the urine, and passes out of the body. Thus, the body loses its main source of fuel even though the blood contains large amounts of glucose.
What Are the Types of Diabetes?
The three main types of diabetes are:
Type 1 diabetes
Type 1 diabetes is an autoimmune disease. An autoimmune disease results when the body's system for fighting infection (the immune system) turns against a part of the body. In diabetes, the immune system attacks the insulin-producing beta cells in the pancreas and destroys them. The pancreas then produces little or no insulin. Someone with type 1 diabetes needs to take insulin daily to live.
At present, scientists do not know exactly what causes the body's immune system to attack the beta cells, but they believe that both genetic factors and environmental factors, possibly viruses, are involved. Type 1 diabetes accounts for about 5 to 10 percent of diagnosed diabetes in the United States.
Type 1 diabetes develops most often in children and young adults, but the disorder can appear at any age. Symptoms of type 1 diabetes usually develop over a short period, although beta cell destruction can begin years earlier.
Symptoms include increased thirst and urination, constant hunger, weight loss, blurred vision, and extreme fatigue. If not diagnosed and treated with insulin, a person can lapse into a life-threatening diabetic coma, also known as diabetic ketoacidosis.
Type 2 diabetes
The most common form of diabetes is type 2 diabetes. About 90 to 95 percent of people with diabetes have type 2. This form of diabetes usually develops in adults age 40 and older and is most common in adults over age 55. About 80 percent of people with type 2 diabetes are overweight. Type 2 diabetes is often part of a metabolic syndrome that includes obesity, elevated blood pressure, and high levels of blood lipids. Unfortunately, as more children become overweight, type 2 diabetes is becoming more common in young people.
When type 2 diabetes is diagnosed, the pancreas is usually producing enough insulin, but, for unknown reasons, the body cannot use the insulin effectively, a condition called insulin resistance. After several years, insulin production decreases. The result is the same as for type 1 diabetes--glucose builds up in the blood and the body cannot make efficient use of its main source of fuel.
The symptoms of type 2 diabetes develop gradually. They are not as sudden in onset as in type 1 diabetes. Some people have no symptoms. Symptoms may include fatigue or nausea, frequent urination, unusual thirst, weight loss, blurred vision, frequent infections, and slow healing of wounds or sores.
Gestational diabetes develops only during pregnancy. Like type 2 diabetes, it occurs more often in African Americans, American Indians, Hispanic Americans, and people with a family history of diabetes. Though it usually disappears after delivery, the mother is at increased risk of getting type 2 diabetes later in life.
What Tests Are Recommended for Diagnosing Diabetes?
The fasting plasma glucose test is the preferred test for diagnosing type 1 or type 2 diabetes. However, a diagnosis of diabetes is made for any one of three positive tests, with a second positive test on a different day:
A random plasma glucose value (taken any time of day) of 200 mg/dL or more, along with the presence of diabetes symptoms.
A plasma glucose value of 126 mg/dL or more, after a person has fasted for 8 hours.
An oral glucose tolerance test (OGTT) plasma glucose value of 200 mg/dL or more in the blood sample, taken 2 hours after a person has consumed a drink containing 75 grams of glucose dissolved in water. This test, taken in a laboratory or the doctor's office, measures plasma glucose at timed intervals over a 3-hour period.
Gestational diabetes is diagnosed based on plasma glucose values measured during the OGTT. Glucose levels are normally lower during pregnancy, so the threshold values for diagnosis of diabetes in pregnancy are lower. If a woman has two plasma glucose values meeting or exceeding any of the following numbers, she has gestational diabetes: a fasting plasma glucose level of 95 mg/dL, a 1-hour level of 180 mg/dL, a 2-hour level of 155 mg/dL, or a 3-hour level of 140 mg/dL.
What Are the Other Forms of Impaired Glucose Metabolism?
People with impaired glucose metabolism, a state between "normal" and "diabetes," are at risk for developing diabetes, heart attacks, and strokes. There are two forms of impaired glucose metabolism.
Impaired Fasting Glucose
A person has impaired fasting glucose (IFG) when fasting plasma glucose is 110 to 125 mg/dL. This level is higher than normal but less than the level indicating a diagnosis of diabetes. Approximately 13.4 million people in the United States, or about 7 percent of the population, have IFG.
Impaired Glucose Tolerance
Impaired glucose tolerance (IGT) means that blood glucose during the oral glucose tolerance test is higher than normal but not high enough for a diagnosis of diabetes. IGT is diagnosed when the glucose level is 141 to 199 mg/dL 2 hours after a person is given a drink containing 75 grams of glucose.
What Are the Scope and Impact of Diabetes?
Diabetes is widely recognized as one of the leading causes of death and disability in the United States. According to death certificate data, diabetes contributed to the deaths of more than 193,140 people in 1996.
Diabetes is associated with long-term complications that affect almost every part of the body. The disease often leads to blindness, heart and blood vessel disease, strokes, kidney failure, amputations, and nerve damage. Uncontrolled diabetes can complicate pregnancy, and birth defects are more common in babies born to women with diabetes.
In 1997, diabetes cost the United States $98 billion. Indirect costs, including disability payments, time lost from work, and premature death, totaled $54 billion; direct medical costs for diabetes care, including hospitalizations, medical care, and treatment supplies, totaled $44 billion.
Who Gets Diabetes?
Diabetes is not contagious. People cannot "catch" it from each other. However, certain factors can increase the risk of developing diabetes.
Type 1 diabetes occurs equally among males and females, but is more common in whites than in nonwhites. Data from the World Health Organization's Multinational Project for Childhood Diabetes indicate that type 1 diabetes is rare in most African, American Indian, and Asian populations. However, some northern European countries, including Finland and Sweden, have high rates of type 1 diabetes. The reasons for these differences are not known.
Type 2 diabetes is more common in older people, especially in people who are overweight, and occurs more often in African Americans, American Indians, Asian and Pacific Islander Americans, and Hispanic Americans. On average, non-Hispanic African Americans are 1.7 times more likely to have diabetes than non-Hispanic whites of the same age. Hispanic Americans are nearly twice as likely to have diabetes as non-Hispanic whites. American Indians have the highest rates of diabetes in the world. Among the Pima Indians living in Arizona, for example, half of all adults have type 2 diabetes.
The prevalence of diabetes in the United States is likely to increase for several reasons. First, a large segment of the population is aging. Also, Hispanic Americans and other minority groups make up the fastest-growing segment of the U.S. population. Finally, Americans are increasingly overweight and sedentary. According to recent estimates, the prevalence of diabetes in the United States is predicted to be 8.9 percent of the population by 2025.
How Is Diabetes Managed?
Before the discovery of insulin in 1921, everyone with type 1 diabetes died within a few years after diagnosis. Although insulin is not considered a cure, its discovery was the first major breakthrough in diabetes treatment.
Today, healthy eating, physical activity, and insulin via injection or an insulin pump are the basic therapies for type 1 diabetes. The amount of insulin must be balanced with food intake and daily activities. Blood glucose levels must be closely monitored through frequent blood glucose checking.
Healthy eating, physical activity, and blood glucose testing are the basic management tools for type 2 diabetes. In addition, many people with type 2 diabetes require oral medication and insulin to control their blood glucose levels.
People with diabetes must take responsibility for their day-to-day care. Much of the daily care involves keeping blood glucose levels from going too low or too high. When blood glucose levels drop too low from certain diabetes medicines--a condition known as hypoglycemia--a person can become nervous, shaky, and confused. Judgment can be impaired. If blood glucose falls too low, a person can faint.
A person can also become ill if blood glucose levels rise too high, a condition known as hyperglycemia.
People with diabetes should see a doctor who helps them learn to manage their diabetes and monitors their diabetes control. An endocrinologist is one type of doctor who may specialize in diabetes care. In addition, people with diabetes often see ophthalmologists for eye examinations, podiatrists for routine foot care, and dietitians and diabetes educators to help teach the skills of day-to-day diabetes management.
The goal of diabetes management is to keep blood glucose levels as close to the normal range as safely possible. A recent major study, the Diabetes Control and Complications Trial (DCCT), sponsored by the National Institute of Diabetes and Digestive and Kidney Diseases (NIDDK), showed that keeping blood glucose levels as close to normal as safely possible reduces the risk of developing major complications of type 1 diabetes.
The 10-year study, completed in 1993, included 1,441 people with type 1 diabetes. The study compared the effect of two treatment approaches--intensive management and standard management--on the development and progression of eye, kidney, and nerve complications of diabetes. Intensive treatment aimed at keeping hemoglobin A-1-c as close to normal (6 percent) as possible. Hemoglobin A-1-c reflects average blood sugar over a 2- to 3-month period. Researchers found that study participants who maintained lower levels of blood glucose through intensive management had significantly lower rates of these complications. More recently, a followup study of DCCT participants showed that the ability of intensive control to lower the complications of diabetes persists up to 4 years after the trial ended.
The United Kingdom Prospective Diabetes Study, a European study completed in 1998, showed that intensive control of blood glucose and blood pressure reduced the risk of blindness, kidney disease, stroke, and heart attack in people with type 2 diabetes.
What Is the Status of Diabetes Research?
NIDDK conducts research in its own laboratories and supports a great deal of basic and clinical research in medical centers and hospitals throughout the United States. It also gathers and analyzes statistics about diabetes. Other Institutes at the National Institutes of Health (NIH) conduct and support research on diabetes-related eye diseases, heart and vascular complications, pregnancy, and dental problems.
Other Government agencies that sponsor diabetes programs are the Centers for Disease Control and Prevention, the Indian Health Service, the Health Resources and Services Administration, the Department of Veterans Affairs, and the Department of Defense.
Many organizations outside of the Government support diabetes research and education activities. These organizations include the American Diabetes Association, the Juvenile Diabetes Foundation International, and the American Association of Diabetes Educators.
In recent years, advances in diabetes research have led to better ways to manage diabetes and treat its complications. Major advances include:
- The development of a quick-acting insulin analog.
- Better ways to monitor blood glucose and for people with diabetes to check their own blood glucose levels.
- Development of external insulin pumps that deliver insulin, replacing daily injections.
- Laser treatment for diabetic eye disease, reducing the risk of blindness.
- Successful transplantation of kidneys and pancreas in people whose own kidneys fail because of diabetes.
- Better ways of managing diabetes in pregnant women, improving chances of successful outcomes.
- New drugs to treat type 2 diabetes and better ways to manage this form of diabetes through weight control.
- Evidence that intensive management of blood glucose reduces and may prevent development of diabetes complications.
- Demonstration that antihypertensive drugs called ACE (angiotensin-converting enzyme) inhibitors prevent or delay kidney failure in people with diabetes.
- Promising results with islet transplantation for type 1 diabetes reported by the University of Alberta in Canada. A nationwide clinical trial funded by the NIH and the Juvenile Diabetes Foundation is currently trying to replicate the Canadian advance.
What Will the Future Bring?
In the future, it may be possible to administer insulin through inhalers, a pill, or a patch. Devices are also being developed that can monitor blood glucose levels without having to prick a finger to get a blood sample.
Researchers continue to search for the cause or causes of diabetes and ways to prevent and cure the disorder. Scientists are looking for genes that may be involved in type 1 or type 2 diabetes. Some genetic markers for type 1 diabetes have been identified, and it is now possible to screen relatives of people with type 1 diabetes to see if they are at risk.
The Diabetes Prevention Trial--Type 1, sponsored by NIDDK, identifies relatives at risk for developing type 1 diabetes and treats them with low doses of insulin or with oral insulin-like agents in the hope of preventing type 1 diabetes. Similar research is under way at other medical centers throughout the world. For more information about this trial, call 1-800-HALT-DM1 (1-800-425-8361).
Transplantation of the pancreas or insulin-producing beta cells offers the best hope of cure for people with type 1 diabetes. Some pancreas transplants have been successful. However, people who have transplants must take powerful drugs to prevent rejection of the transplanted organ. These drugs are costly and may eventually cause other health problems.
Scientists are working to develop less harmful drugs and better methods of transplanting beta cells to prevent rejection by the body. Using techniques of bioengineering, researchers are also trying to create artificial beta cells that secrete insulin in response to increased glucose levels in the blood.
Recently, researchers at the University of Alberta in Edmonton, Canada, announced promising results with islet transplantation in seven patients with type 1 diabetes. At the time of the report in the New England Journal of Medicine, all seven patients who had received the transplant remained free of insulin injections up to 14 months after the procedure.
A clinical trial funded by the NIH and the Juvenile Diabetes Foundation will try to replicate the Edmonton advance. With the insights gained from this trial and other studies, scientists hope to further refine methods of islet harvesting and transplantation and learn more about the immune processes that affect rejection and acceptance of transplanted islets.
For type 2 diabetes, the focus is on ways to prevent diabetes. Preventive approaches include identifying people at high risk for the disorder and encouraging them to lose weight, be more physically active, and follow a healthy eating plan. The Diabetes Prevention Program, another NIDDK project, focuses on preventing the disorder in high-risk populations, such as people with impaired fasting glucose, African Americans, Alaska Natives, American Indians, Asian and Pacific Islander Americans, Hispanic Americans, or women who have had gestational diabetes.
Several new drugs were recently developed to treat type 2 diabetes. By using the oral diabetes medications now available, many people can control blood glucose levels without insulin injections. Studies are under way to determine how best to use these drugs to manage type 2 diabetes. Scientists also are investigating strategies for weight loss in people with type 2 diabetes.