For years doctors have warned of a rising epidemic of diabetes among children. Yet there has been surprisingly little data on the extent of this disease among younger Americans.

A nationally representative study has confirmed that from 2001 to 2009, the incidence of type 1 and type 2 diabetes drastically increased among children and adolescents across racial groups.

The prevalence of type 1 diabetes increased 21 percent among children up to age 19, the study found. The prevalence of type 2 diabetes among those ages 10 to 19 rose 30 percent during the period.

Those are “big numbers,” said Dr. Robin Goland, a co-director of the Naomi Berrie Diabetes Center at Columbia University Medical Center in New York, who has been in practice for about 25 years. “In my career, type 1 diabetes was a rare disease in children, and type 2 disease didn’t exist. And I’m not that old.”

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The analysis, published Saturday in JAMA, the journal of the American Medical Association, includes data from more than 3 million children younger than 20 in five states — California, Colorado, Ohio, South Carolina and Washington — as well as from selected American Indian reservations.

The research was paid for by the Centers for Disease Control and Prevention and the National Institutes of Health and is part of a continuing study, Search for Diabetes in Youth, examining the condition among children.

In type 1 diabetes, a patient’s immune system attacks cells in the pancreas that make insulin, a hormone required to control blood-sugar levels. Historically, children affected by the disease were more often white.

But the new report found the prevalence also has increased among black and Hispanic youngsters. The greatest increase occurred among 15- to 19-year-olds.

“I don’t understand the basis for an increase,” said Goland, who was not involved in the research. “There are a few possibilities, but we need to figure out if it’s something in the environment or something in our genes.”

Some minority youngsters are far less likely to control their high blood sugar and more likely to have complications such as eye disease, kidney disease, heart disease and amputations, said Dr. Dana Dabelea, lead author of the new study and a professor of epidemiology and pediatrics at the Colorado School of Public Health. She called the increase in type 1 diabetes among these children “particularly worrisome.”

Type 2 diabetes used to be called “adult-onset” diabetes because it was so unusual in children. It is thought to be brought on by a genetic predisposition to poor insulin action and secretion, often exacerbated by obesity and inactivity. The new analysis reported increases among black, white and Hispanic children, but not among Asian-Pacific Islander and American Indian children.

The study’s authors speculated that the uptick in type 2 diabetes may result from “minority population growth, obesity, exposure to diabetes in utero and perhaps endocrine-disrupting chemicals.”

The increase will have public-health consequences, the researchers said. More children will enter adulthood at increased risk of early complications, and diabetes is harder to treat in children than in adults. Younger patients also still have reproductive years ahead of them.

“Diabetes in pregnancy is a risk factor for diabetes in the next generation,” Dabelea said.