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Nearly one in four American adolescents may be on the verge of developing Type 2 diabetes or could already be diabetic, representing a sharp increase in the disease’s prevalence among children ages 12 to 19 since a decade ago, when it was estimated that fewer than one in 10 were at risk for or had diabetes, according to a new study.

This worsening of the problem is worrying in light of recently published findings that the disease progresses more rapidly in children than in adults and is harder to treat, experts said.

The study, published online on Monday in the journal Pediatrics, analyzes data from the National Health and Nutrition Examination Survey, which has a nationally representative sample. While it confirmed that teenage obesity and overweight rates had leveled off in recent years and that teenage rates of high blood pressure and high cholesterol had not changed greatly, it found that the percentage of teenagers testing positive for diabetes and prediabetes had nearly tripled to 23 percent in 2007-8 from 9 percent in 1999-2000.

Researchers said the data should be interpreted with caution because the prediabetes and diabetes status of the adolescents was based on a single test of each participant’s fasting blood glucose level, which could be unreliable in children if they had not fasted for at least 8 hours before taking the test. In addition, children this age are going through puberty, a process that induces insulin resistance.

“Nationwide, this is the best sampling of youth to inform us about cardiovascular risk factors,” said Dr. Lori Laffel of the Joslin Diabetes Center in Boston, who was not involved in the study. But she said that the figure of nearly one in four teens having diabetes or prediabetes was high and that the findings needed to be replicated by other researchers in order to support them.

Still, experts and doctors who treat young diabetics said the trend over the past decade was troubling. They were not entirely able to explain why diabetes and prediabetes rates had continued to rise while obesity held steady, but they said it may have taken time for the disease to “catch up” with teenagers who were overweight or sedentary as children.

Other factors may also play a role, including the increasing use of computer and mobile devices that has made youngsters more inactive and the growth of minority ethnic and racial groups who have higher rates of diagnosed diabetes than whites.

The study did not differentiate between adolescents who had diabetes and those with prediabetes, but most are likely to be prediabetic, experts said. That means blood glucose levels are higher than normal, but not high enough to diagnose diabetes.

Many people with prediabetes go on to develop Type 2 diabetes, but they can prevent that from happening with modest weight loss and exercise. The disease, once called adult-onset diabetes because it was so rare in children, if not managed properly causes complications including vision problems, heart disease, nerve damage and kidney failure.

The new study, which included 3,383 participants in different studies over the decade, found that even teenagers of normal weight had risk factors for heart disease, including prediabetes.

Two-thirds of American adolescents ages 12 to 19 are of normal weight, 16 percent are overweight, and another 18 percent are obese; the percentages stayed fairly constant between 1999 and 2008. Sixty percent of those who were found to be obese during the 1999-2008 study, half of the overweight adolescents and 37 percent of the normal weight adolescents had at least one risk factor for heart disease, such as high blood pressure or high cholesterol.

“You see a substantial burden of cardiovascular risk factors even among normal weight kids, and that is certainly something to be concerned about,” said Dr. Ashleigh L. May, an epidemiologist at the Centers for Disease Control and Prevention and the paper’s lead author.

The health survey, which is administered every couple of years, found that the rate of diabetes and prediabetes among adolescents ages 12 to 19 rose from 9 percent in 1999-2000 to 15 percent in 2001-2, with a dip to 13 percent in 2003-4, back up to 16 percent in 2005-6 and then to 23 percent in 2007-8, the most recent years for which data was analyzed.

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