Diabetes is a group of conditions linked by an inability to produce enough insulin and/or to respond to insulin. This causes high blood glucose levels (hyperglycemia) and can lead to a number of acute and chronic health problems, some of them life-threatening.

People with diabetes are unable to process glucose, the body's primary energy source, effectively. Normally, after a meal, carbohydrates 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 someone is unable to produce enough insulin, or if the body's cells are resistant to its effects (insulin resistance), then less glucose is transported from the blood into cells. Blood glucose levels remain high but the body's cells "starve." This can cause both short-term and long-term health problems, depending on the severity of the insulin deficiency and/or resistance. Diabetics typically have to control their blood glucose levels on a daily basis and over time to avoid health problems and complications. Treatment, which may involve specialized diets, exercise and/or medications, including insulin, aims to ensure that blood glucose does not get too high or too low.

  • A very high blood glucose level (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. With severe insulin deficiency, glucose is not available to the cells and 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.
  • A very low blood glucose level (hypoglycemia), often as a result of too much insulin, can also be life-threatening. It can lead to hunger, sweating, irregular and rapid heart beat, confusion, blurred vision, dizziness, fainting, and seizures. Severely low blood glucose can lead fairly quickly to insulin shock and death.
  • Glucose levels that rise over time and become chronically elevated may not be initially noticed. The body tries to control the amount of glucose in the blood by increasing insulin production and by eliminating glucose in the urine. Signs and symptoms usually begin to arise when the body is no longer able to compensate for the higher levels of blood glucose.

Chronic high blood glucose can cause long-term damage to blood vessels, nerves, and organs throughout the body and can lead to other conditions such as kidney disease, loss of vision, strokes, cardiovascular disease, and circulatory problems in the legs. Damage from hyperglycemia is cumulative and may begin before a person is aware that he or she has diabetes. The sooner that the condition is detected and treated, the better the chances are of minimizing long-term complications.

The following table summarizes some types of diabetes.

Type of Diabetes Description
Type 1 Exact cause unknown; thought to be primarily an autoimmune disease that involves the destruction of the insulin-producing beta cells in the pancreas; can occur at any age but usually diagnosed in children and young adults.
Type 2 Most common type; associated with insulin resistance and with insulin production that is insufficient to meet the body's needs and to compensate for resistance. It develops most frequently in overweight middle-aged and elderly people. With increased obesity in children and adolescents, the condition is becoming more common at younger ages.
Gestational Develops during a woman's pregnancy and affects both mother and developing baby; typically develops late in the pregnancy
Prediabetes Higher blood glucose than normal, but not considered diabetes; people with prediabetes are at an increased risk of developing diabetes.
Others A group of less common types of diabetes. Any condition that damages the pancreas and/or affects insulin production or usage can cause diabetes.