The Cleveland Clinic

Diabetes: Type 1 Diabetes

Introduction

Type 1 diabetes occurs when the body's own immune system destroys the insulin-producing cells of the pancreas (called beta cells).

Normally, the body's immune system fights off foreign invaders like viruses or bacteria. But for unknown reasons, in people with type 1 diabetes, the immune system attacks various cells in the body. This results in a complete deficiency of the insulin hormone.

Some people develop a type of diabetes - called secondary diabetes -- which is similar to type 1 diabetes, but the beta cells are not destroyed by the immune system but by some other factor, such as cystic fibrosis or pancreatic surgery.

Understanding Insulin

Normally, the hormone insulin is always secreted by the pancreas in low amounts. When you eat a meal, food stimulates an increase in the amounts of insulin released from the pancreas. The amount that is released is proportional to the amount that is required by the size of that particular meal.

So what does insulin do? Insulin's main role in the body is to help move certain nutrients -- especially a sugar called glucose -- into the cells of the body's tissues. Cells use sugars and other nutrients from meals as a source of energy to run a variety of important processes for the body.

When glucose is moved into cells, the amount of sugar in the blood decreases. Normally that signals the beta cells in the pancreas to stop secreting insulin so that you don't develop low blood sugar levels (hypoglycemia). But the destruction of the beta cells that occurs with type 1 diabetes throws the entire process into disarray.

In people with type 1 diabetes, glucose isn't moved into the cells because insulin is not available. When glucose builds up in the blood instead of going into cells, the body's cells starve for nutrients and other systems in the body must provide energy for many important bodily functions. As a result, high blood glucose develops and can cause:

  • Dehydration. The build up of sugar in the blood can cause an increase in urination (to try to clear the sugar from the body). When the kidneys lose the glucose through the urine, a large amount of water is also lost, causing dehydration.
  • Weight loss. The loss of sugar in the urine means a loss of calories which provide energy and therefore many people with high sugars lose weight. (Dehydration also contributes to weight loss.)
  • Diabetic ketoacidosis (DKA). Without insulin and because the cells are starved of energy, the body breaks down fat cells. One of the products of fat break down is a specific type of acid that can be used by the brain for energy. Unfortunately none of the body's other cells can use this acid for energy, and thus continue to starve without insulin. So, the liver releases the sugar it stores to help out. Since the body cannot use these sugars without insulin, more sugars piles into the blood stream. The combination of high excess sugars, dehydration and acid build up is known as "ketoacidosis" and can be life-threatening if not treated immediately.
  • Damage to the body. Over time, the high glucose levels in the blood may damage the nerves and small blood vessels of the eyes, kidneys, and heart and predispose a person to atherosclerosis (hardening) of the large arteries that can cause heart attack and stroke.

Who Gets Type 1 Diabetes?

Although the disease usually starts in people under the age of 20, type 1 diabetes may occur at any age.

The disease is relatively uncommon, affecting 1 in 250 Americans. The condition is more common in whites than in blacks and occurs equally in men and women.

What Causes Type 1 Diabetes?

Doctors don't know all the factors that lead to type 1 diabetes. Clearly, the susceptibility to the condition can be inherited.

Doctors have identified that an environmental trigger plays a role in causing the disease. Type 1 diabetes appears to occur when something in the environment -- a toxin or a virus (but doctors aren't sure) -- triggers the immune system to mistakenly attack the pancreas and destroy the beta cells of the pancreas to the point where they can no longer produce sufficient insulin. Markers of this destruction -- called autoantibodies -- can be seen in most people with type 1 diabetes. In fact, they are present in 85% to 90% of people with the condition when the blood sugars are high.



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