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Diabetes Mellitus, disease caused by defective carbohydrate metabolism and characterized by abnormally large amounts of sugar in the blood and urine. Diabetes mellitus affects approximately 1 to 2 per cent of the population, up to half of whom remain undiagnosed. Diabetes mellitus can eventually damage the eyes, kidneys, heart, and limbs, and can endanger pregnancy. Proper treatment, however, can minimize these complications.

Diabetes Mellitus is usually classified into two types. Type-I, or insulin-dependent diabetes mellitus (IDDM), formerly called juvenile-onset diabetes, which occurs in children and young adults, has been implicated as one of the autoimmune diseases. Rapid in onset and progress, it accounts for about 10 to 15 per cent of all cases. Type-II, or non-insulin-dependent diabetes mellitus (NIDDM), formerly called adult-onset diabetes, is usually found in people over 40 years old and progresses slowly. Often it is not accompanied by clinical symptoms and is detected instead by elevated blood or urine glucose levels.

Cause and Course

Diabetes is considered a group of disorders with multiple causes, rather than a single disorder. The human pancreas secretes a hormone called insulin that facilitates the entry of the sugar glucose into all tissues of the body, providing energy for bodily activities. In a person with diabetes, however, the entry of glucose is impaired, a result either of a deficiency in the amount of insulin produced or of altered receptor cells. Consequently, sugar builds up in the blood and is excreted in the urine. In the Type-I diabetic, the problem is almost always a severe or total reduction in insulin production. In the Type-II diabetic, the pancreas makes a considerable quantity of insulin, but it is insufficient for the needs of the body, especially as the body tissues are frequently resistant to the actions of insulin. In some individuals this resistance is due to prolonged obesity: a high level of blood sugar inactivates the tissue components, which, in turn, act as a target for insulin.

If untreated, Type-I diabetes can be quickly fatal. It is accompanied by extreme thirst, weight loss, and fatigue. Because the body lacks sufficient energy from tissue glucose, it begins to break down stored fat. This produces increasing amounts of compounds called ketone bodies in the blood, making the blood acidic and interfering with respiration. Death from diabetic coma was the usual outcome of the disease before the discovery of insulin therapy in the 1920s. In both forms of diabetes, moderately elevated blood-sugar levels for many years can eventually cause: kidney disease; impairment of sight due to rupture of blood vessels in the eyes; reduction of blood flow to the limbs, which can cause numbness and sometimes necessitates amputation; and alterations in nervous sensation. Diabetics also have an increased risk of heart attack and stroke. Uncontrolled diabetes in a pregnant woman is associated with increases in stillbirths and birth abnormalities. The life span of an inadequately treated diabetic is shortened by about one-third.

Detection of Type-II diabetes in the absence of symptoms starts with measurement of the glucose level in urine. If a high level is detected, the amount of blood sugar is measured after an overnight fast. A high value indicates diabetes, and those with a normal level then undergo an oral glucose tolerance test in which the amount of glucose in the blood is measured after ingestion of a large amount of the sugar.

Treatment

With adequate treatment most diabetics maintain blood-sugar levels within a normal or nearly normal range. This enables them to live normal lives and prevents some long-term consequences of the disease. For the Type-I or Type-II diabetic with little or no insulin production, therapy involves insulin injections and changes in diet. The diet requires distributing meals and snacks throughout the day so that the insulin supply is not overwhelmed, and eating food that contains polysaccharides rather than simple sugars. (Polysaccharides must first be broken down in the stomach, therefore producing a much slower rise in blood sugar.) For Type-II diabetics, most of whom are at least moderately overweight, the basics of therapy are diet control, weight reduction, and exercise. Weight reduction appears partially to reverse the condition of insulin resistance in the tissues. If a patient's blood-sugar level is still high, the doctor may add insulin injections. An oral sugar-lowering agent may be prescribed for individuals who do not require insulin addition to control their diabetes, as well as for those who have trouble injecting themselves or whose diabetes is not controlled by insulin addition.

Some diabetic patients are now equipped with insulin pumps, carried on the body, that deliver insulin at preset times and rates. Such pumps improve control over blood-sugar levels, although acute but nonfatal complications such as ketoacidosis and infection of the infusion site are sometimes observed.