WHAT IS DIABETES MELLITUS?

by Arturo Rolla, MD and Joan Stout

Diabetes is a metabolic disorder that occurs when the body cannot properly use glucose (a form of sugar), the body's main source of fuel. During digestion, most of the carbohydrates we eat are converted to glucose, which passes into the bloodstream where it is available to the cells for use as energy. 80% of the glucose in the blood goes to the muscles. But in order for glucose to enter the cells and be used as energy, insulin, a hormone secreted in the islets of the pancreas, must be present. Without insulin, the body cannot convert food into energy.

The cells that produce insulin are called beta cells. They are normally stimulated to produce insulin by the rising level of blood glucose. In that way, the body has a system by which the right amount of insulin is secreted for the right amount of glucose present. Once the glucose has entered the cells, the blood glucose level decreases, and the beta cells stop secreting insulin.

Q: What are the different types of diabetes?

A: There are basically two types of diabetes. In one type, the beta cells are destroyed by the immune system and no longer secrete insulin. This is called type I diabetes and is characterized by an absolute deficit of insulin. The other type, called type II diabetes, is due to "insulin resistance," an initial resistance of the body's cells to obey the orders of insulin. To overcome this resistance, the beta cells secrete more insulin, and glucose is eventually forced into the cells. Glucose is maintained within normal limits, but at the expense of increased insulin secretion by the beta cells. After many years of such increased secretion, the beta cells become "tired" from working overtime, and the fatigue process begins. This fatigue tends to be progressive, and in time the compensation of insulin resistance disappears. At that point, blood glucose levels start going up.

Type I diabetes is also called insulin-dependent diabetes (IDDM) and was previously known as juvenile diabetes. We now recognize that type I can appear at any age, even though it is most often diagnosed before the age of 40. Type I is an autoimmune disease, which means that the body's defense against infection, the immune system, attacks part of the body. In type I, the immune system attacks the beta cells in the islets of the pancreas and destroys them. The pancreas then produces very little or no insulin, and the patient needs daily insulin injections to live. Symptoms typically appear over a brief period of time, although the destruction of the beta cells may occur over a period of months or years. These symptoms include: Increased thirst and urination, weight loss despite increased hunger and food intake, blurred vision, extreme tiredness, and itching. Coma and death can follow if diabetes is not diagnosed and treated.

Type II diabetes is also called noninsulin-dependent diabetes (NIDDM) and was previously known as adult-onset diabetes. Type II usually occurs in adults over 40, but it can appear at a much earlier age, including early adolescence (maturity-onset diabetes of the young, MODY). About 80% of people diagnosed with type II diabetes are overweight. In type II, the pancreas produces insulin, but the body is unable to effectively use the insulin. Insulin resistance is common, and the patient may have large amounts of insulin present in the bloodstream. Symptoms of type II typically develop gradually, over a period of months or years. Symptoms include: Increased thirst, increased urination (especially at night), fatigue, weight loss, blurred vision, frequent infections, and slow healing of sores. Because type II can be present for many years before diagnosis, symptoms may include complications of diabetes, such as heart disease, kidney disease, nerve problems, or vision problems.

Q: What causes type I diabetes?

A: At this point, we do not know why the body's immune system attacks the beta cells and destroys them. The cause may be a virus, an exposure to cow's milk at an early age, genetics, or more likely a combination of factors. Doctors can determine who is at a high risk of developing type I by testing their blood for antibodies against the islets in the pancreas and by testing their capacity to secrete insulin. The hope is to prevent further beta cell destruction.

Q: What causes type II diabetes?

A: Most people who develop type II diabetes are overweight. Overweight people have excess adipose tissue in the body, and the extra fat increases their resistance to insulin, not only in the fat tissues but also in all the other cells. Diabetes is not caused by eating too much sugar, but being overweight increases the chances of developing type II diabetes.

Q: Who gets diabetes?

A: The following people have an increased risk for developing diabetes:

• people with family members who have diabetes
• people who are overweight
• African Americans
• Native Americans
• Hispanics

These risk factors are much higher for type II than for type I, although a genetic component is present for both types. For type II diabetes, risk factors include older age, increased weight, decreased level of physical activity, overfeeding or too rich diet, and family history of diabetes. Adults are much more likely to get type II diabetes than are children, while type I tends to appear more frequently in children.

Q: How many people have diabetes?

A: In 1995, the estimated prevalence of diabetes in the United States was 16 million people, about half of them not yet diagnosed. For type I diabetes, the estimate of diagnosed cases ranges up to 800,000. About 30,000 new cases of type I are diagnosed each year. For type II diabetes, the 1993 estimate was 7 to 7.5 million diagnosed cases. About 595,000 new cases of type II are diagnosed each year. Approximately 4.2 million women and 3.6 million men have been diagnosed with diabetes. For children age 19 years or younger, the estimate is 100,000 cases. For adults age 65 years or older, the estimate is 3.2 million cases.

Q: How is diabetes treated?

A: Daily insulin injections are required to treat type I diabetes. Many people with type I take multiple injections daily. A regimen of three or more injections per day is called "tight control" or "intensive management." The insulin must be balanced properly with food intake and exercise (including regular daily activities). Frequent blood testing is performed by the patient to monitor blood sugar levels. This involves pricking a finger for a drop of blood, applying the blood to a test strip, and inserting the strip into a small machine that reads the strip and displays the approximate level of blood sugar. Type II is sometimes treated with diet and exercise only. Oral diabetes medications, which are not insulin, are also used. If these methods do not work, type II is treated with insulin. People with type II must also balance their exercise and food intake with their medication (whether oral medication or insulin). A weight loss diet is frequently a part of treatment with type II. Blood glucose testing by the patient is also an important part of treatment.

Both type I and type II diabetes are best treated with a team approach, with the patient being the most important part of the team. The goal of treatment is to keep blood sugar levels as close to normal as possible and so prevent long-term complications. As most of the daily care is the responsibility of the person who has diabetes, patient education is imperative. Other team members should include a diabetes doctor (endocrinologist or diabetologist), specialists as necessary (ophthalmologist, podiatrist, and so on), a dietitian, and a diabetes educator.

A 10-year study called the Diabetes Control and Complications Trial (DCCT) was completed in 1993. The study included over 1,400 people with type I diabetes and compared the results of intensive management with "standard" management. The participants who followed intensive management, keeping their blood sugar at lower levels, had significantly lower rates of eye, kidney, and nerve diseases than did the "standard management" group. Although the study only focused on type I diabetes, most doctors believe that people with type II will also benefit from keeping their blood sugar as close to normal as possible.

Q: What are the complications of diabetes?

A: Complications of both type I and type II include eye disease and blindness, heart disease, strokes, kidney disease and kidney failure, amputations, nerve damage, skin infections, and gum disease. Diabetes can also cause complications of pregnancy and congenital malformations. In 1992, diabetes contributed to at least 169,000 deaths. In 1993, diabetes was the seventh leading cause of death listed on death certificates in the United States.

Q: How much does diabetes cost?

A: In 1992, the total cost of diabetes in the United States was estimated at $92 billion. This includes $45 billion for direct medical costs (only those costs directly attributable to diabetes) and $47 billion for indirect costs such as disability, work loss, and premature deaths.

Arturo Rolla, MD, is an endocrinologist at New England Deaconess Hospital and an associate clinical professor of medicine at Harvard Medical School. Joan Stout is a professional writer and editor.