Diabetes mellitus, often simply
diabetes, is a syndrome characterized by disordered metabolism and
inappropriately high blood sugar (hyperglycaemia) resulting from either low
levels of the hormone insulin or from abnormal resistance to insulin's effects
coupled with inadequate levels of insulin secretion to compensate.
The characteristic symptoms are excessive urine production (polyuria),
excessive thirst and increased fluid intake (polydipsia), and blurred vision;
these symptoms may be absent if the blood sugar is mildly elevated.
The World Health Organization recognizes three main forms of diabetes mellitus:
type 1, type 2, and gestational diabetes (occurring during pregnancy),
which have similar signs, symptoms, and consequences, but different
causes and population distributions. While, ultimately, all forms are due to the
beta cells of the pancreas being unable to produce sufficient insulin to prevent
hyperglycemia, the causes are different. Type 1
diabetes is usually due to autoimmune destruction of the pancreatic beta cells,
which produce insulin. Type 2 diabetes is characterized by insulin resistance in
target tissues, this causes a need for abnormally high amounts of insulin and
diabetes develops when the beta cells cannot meet this demand. Gestational
diabetes is similar to type 2 diabetes in that it involves insulin resistance;
the hormones of pregnancy can cause insulin resistance in women genetically
predisposed to developing this condition.
Gestational diabetes typically resolves with delivery of the child, however
types 1 and 2 diabetes are chronic conditions. All
types have been treatable since insulin became medically available in 1921. Type
1 diabetes, in which insulin is not secreted by the pancreas, is directly
treatable only with injected or inhaled insulin, although dietary and other
lifestyle adjustments are part of management. Type 2 may be managed with a
combination of dietary treatment, tablets and injections and, frequently,
insulin supplementation. While insulin was originally produced from natural
sources such as porcine pancreas, most insulin used today is produced through
genetic engineering, either as a direct copy of human insulin, or human insulin
with modified molecules that provide different onset and duration of action.
Insulin can also be delivered continuously by a specialized pump which
subcutaneously provides insulin through a changeable catheter.
Diabetes can cause many complications. Acute complications (hypoglycemia,
ketoacidosis or nonketotic hyperosmolar coma) may occur if the disease is not
adequately controlled. Serious long-term complications include cardiovascular
disease (doubled risk), chronic renal failure, retinal damage (which can lead to
blindness), nerve damage (of several kinds), and microvascular damage, which may
cause impotence and poor healing. Poor healing of wounds, particularly of the
feet, can lead to gangrene, which may require amputation. Adequate treatment of
diabetes, as well as increased emphasis on blood pressure control and lifestyle
factors (such as not smoking and keeping a healthy body weight), may improve the
risk profile of most aforementioned complications. In the developed world,
diabetes is the most significant cause of adult blindness in the non-elderly,
the leading cause of non-traumatic amputation in adults, and diabetic
nephropathy is the main illness requiring renal dialysis.