Diabetes is a chronic disease caused by inherited and/or acquired deficiency in production of insulin by the pancreas, or in its effect. Insulin is the hormone that helps glucose get into cells where it is used as a source of energy. As a result of insulin deficiency, or insulin resistance, the body is unable to metabolize sugar and other foods efficiently. Persons with diabetes suffer from extreme thirst (polydipsia), hunger, weakness or lassitude, and loss of weight. They excrete abnormally large quantities of urine (polyuria) of high specific gravity, containing glucose and other substances not normally present. These symptoms may be less marked in non-insulin dependent (adult) diabetes. Very susceptible to infection, the diabetic's most serious complication is ketoacidosis with or without coma, formerly the major cause of death, but absent in well-treated patients. Major chronic complications are cardiovascular disease leading to heart attack and stroke, retinal eye disease which may sometimes lead to blindness, renal disease which may cause kidney failure, and peripheral vascular disease and neuropathy which may lead to infection and gangrene that would ultimately require amputation of limbs.
For all insulin-dependent diabetics, and some non-insulin dependent diabetics, daily injections of insulin are essential. However, in many parts of the world insulin is scarce, of uneven quality, or priced beyond the reach of the insulin-dependent person. A shortage of nursing and allied health professional who play a major role in the delivery of diabetes health care further exacerbates the problem.
The relationship of the pancreas to diabetes was first suggested by Cawley, an English physician, in 1788. In 1921, insulin was found by Banting and Best to revert clinical symptoms. Before insulin was available, fewer than 25% of patients with the severe form of the disease lived for more than 10 years, children rarely for more than one year. Today, life expectancy and health prognosis are limited by vascular and neural complications with progressive dysfunction of kidneys, heart and coronary vessels, retina, autonomic and peripheral nervous system. Knowledge of the disease is still rudimentary, although hereditary predisposition for diabetes is well-established, more so in type II than in type I. In type I, susceptibility may be conveyed by genes close to the histocompatibility genes DR-3 and DR-4 on chromosome 6. Manifestation of this type seems to require additional exogenous influences. Malnutrition-related diabetes has also been described from some developing countries, but this form is still poorly understood. The proportion of persons with diabetes in the population is estimated to be two or three percent, about half of whom are unaware of their disease, but only 5 in 100 of these are primarily insulin dependent (type I).
One way doctors diagnose diabetes is through an oral glucose tolerance test. A fasting person drinks a known dose of glucose. Over the next two hours, blood sugar is measured at prescribed intervals. This is an accurate way to evaluate diabetes, but it is time-consuming and cumbersome.
The most common diagnostic test physicians utilize is known as the glycosylated hemoglobin test, abbreviated HbA1c. This is preferable to a single measurement of blood sugar because it gives a snapshot of glucose levels in the blood over the past several weeks. It is far more convenient than the oral glucose tolerance test, though it may not be quite as accurate.
In 1996 there were about 150 million diabetics worldwide. That number is expected to more than double by 2025.
Diabetes is a common disease from which no age-group is exempt. Most at risk are the obese, the elderly, those with a family history of diabetes or a previous diagnosis of diabetes during pregnancy, and persons with elevated blood pressure and blood lipids. Type I, or insulin-diabetes, has a rapid onset and more severe course, occurs when the pancreas fails to produce insulin; it occurs predominantly in young persons and requires insulin from the time of diagnosis. Type II diabetes, or non-insulin diabetes, is much more common, and results from the body's inability to respond properly to the action of insulin. It has a more gradual onset and occurs preponderantly in older people, affecting more women than men and associated with obesity. It can be treated with insulin, but usually can be managed by drugs which lower blood glucose levels, together with adjustment of diet and physical exercise. Overall, at least 2% of the world's adult population, or 60 million people, are believed to suffer from diabetes. The risk of insulin-dependent diabetes is inheritable; non-insulin dependent diabetes is not clearly genetically linked but is strong familial. Since diabetes becomes more common with advancing age, in an aging population the lifetime risk of diabetes (to the individual) is higher than these prevalence estimates. Diet is important for diabetics, with fatty food forbidden and unrefined carbohydrates (such as brown bread, porridge and potatoes) recommended because of their high fibre content.
In the USA, 95% of amputations because of gangrene are performed on diabetic people. Diabetics suffer 75% of all strokes, and make up the majority of the blind, diabetic retinopathy being caused by blood platelet aggregation due to high blood fats.
A 1996 US study of more than 112,000 female nurses, followed for 12 years, showed that current smokers face an increased risk of developing noninsulin-dependent diabetes, with the risk increasing with the number of cigarettes smoked. Another study of 43,000 male health professionals showed that smoking 25 or more cigarettes a day doubled a man's risk of developing diabetes.
Diabetes is more common in some Native American groups than it is in the general American population.