Diabetes mellitus is the name given to a group of conditions linked by the patient’s inability to produce and/or utilize insulin and that lead to high blood glucose (sugar) levels. It is not to be confused with diabetes insipidus, a more rare condition that is associated with symptoms similar to those of diabetes mellitus but that has a different cause. Although the two share the same term “diabetes” (which means increased urine production), the term diabetes, when used by itself, is often used to refer to diabetes mellitus and will be used that way in this article.

According to the National Institute of Diabetes and Digestive and Kidney Diseases (2005 data), about 20 million people in the United States have diabetes, but as many as 6 million of them are not yet aware that diabetes is affecting their health. Diabetes disrupts the normal balance between insulin and glucose. After a meal, carbohydrates usually are broken down into glucose and other simple sugars. This causes blood glucose levels to rise and stimulates the pancreas to release insulin into the bloodstream.

Insulin is a hormone produced by the beta cells in the pancreas. It regulates the transport of glucose into most of the body’s cells and works with glucagon, another pancreatic hormone, to maintain blood glucose levels within a narrow range. If there is insufficient or ineffective insulin, or if the body’s cells are resistant to its effects (insulin resistance), glucose levels remain high in the bloodstream and the body’s cells “starve.” This can cause both acute and chronic problems depending on the severity of the insulin deficiency. Most tissues in the body rely on glucose for energy production and all but a few – such as the brain and nervous system – are entirely reliant on insulin-mediated transportation.

Acute hyperglycemia can be a medical emergency. The body tries to rid the blood of excess glucose by flushing it out of the system with increased urination. This process can cause dehydration and upset the body’s electrolyte balance as sodium and potassium are lost in the urine. Since glucose is not available to the cells with severe insulin deficiency, the body may attempt to provide an alternate energy source by metabolizing fatty acids. This less efficient process leads to a buildup of ketones and upsets the body’s acid-base balance, producing a state known as ketoacidosis. Left unchecked, acute hyperglycemia can lead to severe dehydration, loss of consciousness, and even death.

Glucose levels that rise over time and become chronically elevated may not be initially noticed by the patient. The body tries to control the amount of glucose in the blood by increasing insulin production and by excreting glucose in the urine. Symptoms usually begin to arise when the body is no longer able to compensate for the higher levels of blood glucose. Chronic hyperglycemia can cause long-term damage to blood vessels, nerves, and organs throughout the body and can lead to other conditions such as renal failure, loss of vision, strokes, and cardiovascular disease; diabetes also commonly leads to circulatory problems in the legs. Damage from hyperglycemia is cumulative and may begin before a patient is aware that he or she has diabetes. The sooner that the condition is detected and treatment started, the better the chances of minimizing complications.