What is Type 1 Diabetes?

Dr. Greene's Answer

Until June 23, 1997, type 1 diabetes was also called insulin-dependent diabetes mellitus (IDDM). Normally, a hormone called insulin pushes sugar from the blood into the body’s cells where it can be used for fuel. The concentration of sugar in the blood remains within a fairly narrow range. If the body stops making insulin (type 1 diabetes), then adequate sugar doesn’t get into the cells.

Actually, all of us are insulin dependent; it’s just that some of us stop producing our own and need insulin injections. Without insulin, muscle and fat begin to be burned for fuel (evidence of this — ketones — shows up in the urine). The person feels hungry all the time, but loses weight in spite of increased eating. Without replacement insulin, the person would eventually starve to death. Meanwhile, the concentration of sugar in the blood begins to increase. We call it diabetes when the fasting blood sugar is at or above 126 mg/dL. When the level reaches around 180 mg/dL, the sugar begins to spill over into the urine. This causes the person to make more urine and then to get thirstier, creating an accelerating cycle.

The classic symptoms of type 1 diabetes, then, are increased urination (polyuria), increased thirst (polydipsia), increased eating (polyphagia) and weight loss. Anyone with the classic symptoms should have a blood sugar test as well as a urine test. Occasionally people also report fatigue, blurred vision, vomiting, abdominal pain, or frequent skin infections. If the disease remains undiagnosed, symptoms progress to include labored breathing, coma, and death.

People who get type 1 diabetes were born with a genetic predisposition to it. Not everyone born with this predisposition gets diabetes, however. In fact, if an identical twin has diabetes, the other twin gets it only about half the time. Along the way, some of the predisposed individuals are exposed to something in the environment that triggers the diabetes. Scientists believe this is usually a viral infection. The virus misleads the body’s immune system into making antibodies against its own pancreas cells that make insulin. (This is why type 1 diabetes is now also called immune-mediated diabetes.)

The insulin-producing cells of the pancreas are gradually destroyed over time. When 90% of them have been destroyed, the person suddenly begins to develop symptoms. Thus, insulin-dependent diabetes generally brews for years, but appears abruptly. It rarely goes undiagnosed for more than a few weeks.

Immune-mediated or type 1 diabetes most often strikes young people, especially between the ages of 5 and 7 (when viruses run through the schools), or at the time of puberty (when so many hormones change). For this reason, it used to be called juvenile-onset diabetes. This term has now been eliminated, since we now know that it can appear at any age. Currently, over a million people in the United States have type 1 diabetes. It is estimated that one in every 400-600 children and adolescents has type 1 diabetes. About 30,000 people develop it each year, and their lives will never be the same.