ATLANTA (AP) -- Half the nation's overweight teens have unhealthy blood pressure, cholesterol or blood sugar levels that put them at risk for future heart attacks and other cardiac problems, new federal research says.

And an even larger proportion of obese adolescents have such a risk, according to the alarming new numbers.

"What this is saying, unfortunately, is that we're losing the battle early with many kids," said Dr. Stephen Daniels, a University of Colorado School of Medicine expert who was not involved in the study.

People can keep their risk of heart disease very low if they reach age 45 or 50 at normal weight and with normal blood pressure, normal cholesterol and no diabetes. So these results are not good, he said.

The study was released Monday in the journal Pediatrics.

The Centers for Disease Control and Prevention research focused on 3,383 adolescents ages 12 through 19. The youths were part of an intensive national study that involves interviewing, weighing, measuring and performing medical tests on people across the country.

The ongoing CDC study is considered a gold standard for looking at national health trends, said Dr. William Mahle, an Emory University pediatric cardiologist.

So there was some good news, Mahle said, that the study found no increase in levels of obesity, high blood pressure or bad cholesterol during the years it covered -- 1999 through 2008.

"All of us are looking for some sign or signal that we're making headway," said Mahle, who was not involved with the study. "So that was reassuring."

But one measure did get worse: The percentage of adolescents who were diagnosed with diabetes or pre-diabetes rose dramatically, from 9 percent to 21 percent. Pre-diabetics have higher than normal blood sugar levels, but not high enough to count as diabetes.

It's not clear why the proportion of kids with high blood sugar would increase while the measures for the other heart disease risk factors held steady. It may have something to do with the kind of test used to measure blood sugar, Daniels said.

Adolescents in the study were given a blood test that can give varying results depending on the day or time of day the test is given. Other tests, though more involved and more expensive, are considered more precise.

Daniels said it's possible another testing method might not have produced a swing so large.

That is possible, said Ashleigh May, the CDC epidemiologist who was the study's lead author.

"This study is just a first step to identify problems in youth. More work needs to be done to identify why this is happening and the advantages of using various test methods in this population," she said.

Overall the study found that 50 percent of overweight youths and 60 percent of obese youths had at least one risk factor for future heart disease.

But normal-weight kids aren't off the hook -- 37 percent had at least one risk factor and could face increased chances for heart trouble as adults, the study suggests.

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