Updated

In the first major national analysis of diabetes trends among American youth, researchers Saturday reported an alarming 23% rise in type 1 diabetes incidence over an eight-year period ending in 2009.

The surprising increase, being reported at a meeting of the American Diabetes Association, comes amid similar growth of type 2 diabetes in children. But unlike type 2, which is linked to the high prevalence of obesity in youth, researchers have no explanation for why the autoimmune form of the disease is growing at such a clip.

Funded by the Centers for Disease Control and Prevention and the National Institutes for Health, the study used data from 20,000 children and youth under 20 at multiple hospitals and health centers in five states. The researchers found that the incidence of type 2 diabetes over that period increased 21%.

"This is of grave concern, because these youth will live with diabetes most of their lives and may develop diabetes-related complications," Guiseppina Imperatore, a medical epidemiologist at CDC, said in a statement. "Preliminary data suggest that complications may already be developing in this generation."

The study found that children and adolescents with diabetes have measurable signs of complications including nerve damage that could lead to amputations. It also identified early signs of cardiovascular damage raising risks for future heart disease.

CDC estimates that there are 18.8 million Americans who have been diagnosed with both types of diabetes and another 7 million undiagnosed, costing $116 billion in direct medical costs. Of those, between 5% and 10% are thought to have type 1 diabetes.

Another study released Saturday found most people with type 1 don't meet treatment targets and they are likely to be overweight or obese as adults. Failure to reach treatment targets such as the level of A1C blood hemoglobin levels, a common measurement of blood glucose, raises the risk for complications.

That study analyzed data from the T1D Exchange Clinic Registry which collects medical information from 25,000 volunteer participants of all ages from 67 clinics around the country.

Type 1 diabetes, formerly known as juvenile diabetes, is an autoimmune disorder where the body loses the ability to produce insulin, the hormone that controls the level of sugar in the blood. Type 2 diabetes is characterized by insulin resistance or the inability to produce sufficient levels of insulin. Type 1 diabetics are insulin dependent while type 2 diabetics in many cases can manage the disease with changes to diet and exercise.

Rising at a rate of 3% a year incidence of type 1 diabetes nearly doubles every 20 years. "We are definitely seeing this more in children. Children under the age of 5 are where we are seeing the biggest increase," Georgeanna Klingensmith, head of pediatrics at the Barbara Davis Center for Childhood Diabetes, said in an interview. "The day cares and school systems need to be prepared to deal with that."

The growth in type 1 stumps researchers who haven't been able to identify what triggers the autoimmune response or explain why an increasing number of people are afflicted. About 80% of type 1 diabetics don't have a close relative with the disease.

"We are not quite sure of all the triggers—genetic and environmental," Richard Bergenstal, executive director of the International Diabetes Center, told a news briefing.

Click for more from The Wall Street Journal