Introduction
The two major forms of diabetes are type 1 (previously called insulin-dependent diabetes mellitus, IDDM, or juvenile-onset diabetes) and type 2 (previously called noninsulin-dependent diabetes mellitus, NIDDM, or maturity-onset diabetes).
Insulin
Both type 1 and type 2 diabetes share one central feature: elevated blood sugar (glucose) levels due to insufficiencies of insulin, a hormone produced by the pancreas. Insulin is a key regulator of the body's metabolism. It works in the following way:
- During and immediately after a meal the process of digestion breaks down carbohydrates into sugar molecules (including glucose) and proteins into amino acids.
- Right after the meal, glucose and amino acids are absorbed directly into the bloodstream, and blood glucose levels rise sharply.
- The rise in blood glucose levels signals important cells in the pancreas, called beta cells, to secrete insulin, which pours into the bloodstream. Within 10 minutes after a meal, insulin rises to its peak level.
- Insulin enables glucose to enter cells in the body, particularly muscle and liver cells. Here, insulin and other hormones direct whether glucose will be burned for energy or stored for future use.
- When insulin levels are high, the liver stops producing glucose and stores it in other forms until the body needs it again.
- As blood glucose levels reach their peak, the pancreas reduces the production of insulin.
- About 2 - 4 hours after a meal, both blood glucose and insulin are at low levels, with insulin being slightly higher. The blood glucose levels are then referred to as fasting blood glucose concentrations.
Type 2 Diabetes
Type 2 diabetes is the most common form of diabetes, accounting for 90 - 95% of cases. In type 2 diabetes, the body does not respond properly to insulin, a condition known as insulin resistance. The disease process of type 2 diabetes involves:
- The first stage in type 2 diabetes is insulin resistance. Although insulin can attach normally to receptors on liver and muscle cells, certain mechanisms prevent insulin from moving glucose (blood sugar) into these cells where it can be used. Most patients with type 2 diabetes produce variable, even normal or high, amounts of insulin. In the beginning, this amount is usually sufficient to overcome such resistance.
- Over time, the pancreas becomes unable to produce enough insulin to overcome resistance. In type 2 diabetes, the initial effect of this stage is usually an abnormal rise in blood sugar after a meal (called postprandial hyperglycemia).
- Eventually, the cycle of elevated glucose further damages beta cells, thereby drastically reducing insulin production and causing full-blown diabetes. This is made evident by fasting hyperglycemia, in which elevated glucose levels are present most of the time.
Type 1 Diabetes
In type 1 diabetes, the body does not produce insulin. Onset is usually in childhood or adolescence. Type 1 diabetes is considered an autoimmune disorder that involves:
- Beta cells in the pancreas that produce insulin are gradually destroyed. Eventually insulin deficiency is absolute.
- Without insulin to move glucose into cells, blood glucose levels become excessively high, a condition known as hyperglycemia.
- Because the body cannot utilize the sugar, it spills over into the urine and is lost.
- Weakness, weight loss, frequent urination, and excessive hunger and thirst are among the initial symptoms.
- Patients with type 1 diabetes need to take daily insulin for survival. [For more information, see In-Depth Report #9: Diabetes - type 1.]
Gestational Diabetes
About 5% of pregnant women develop a form of type 2 diabetes, usually temporary, in their third trimester called gestational diabetes.
Gestational diabetes is diabetes that first appears during pregnancy. It usually develops during the third trimester of pregnancy. After delivery, blood sugar (glucose) levels generally return to normal, although up to 25% of these women develop type 2 diabetes within 15 years.
Because glucose crosses the placenta, a pregnant women with diabetes can pass high levels of blood glucose to the fetus. This can cause excessive fetal weight gain, which can cause delivery complications as well as increased risk of breathing problems and higher future risk for the child to develop obesity and type 2 diabetes. In addition to endangering the fetus, gestational diabetes can also cause serious health risks for the mother, such as preeclampsia, a condition that involves high blood pressure during pregnancy.
