New federal research finds that half of overweight adolescents in the U.S. have unhealthy blood pressure, cholesterol or blood sugar levels that significantly increase their risk for future cardiovascular diseases.

Experts at the Centers for Disease Control and Prevention said that an even larger proportion of obese teens are at risk for future heart attacks and cardiac problems, according to findings published Monday in the journal Pediatrics.

The number of teens between the ages of 12 to 19 with prediabetes or diabetes has more than doubled from 9 percent in 1999 to 23 percent in 2008, according to researchers.

Cardiovascular disease, which often leads to stroke and heart attacks, is the leading cause of death among adults living in the U.S., and while heart attacks and strokes usually don’t happen until adulthood, researchers found that many of the teens participating in the nationally representative study had a substantial number of cardiovascular risk factors.

Although the prevalence of cardiovascular disease risk factors was more prominent in overweight and obese adolescents, at 49 percent and 61 percent respectively, researchers found that 37 percent of adolescents with normal weight have one or more cardiovascular disease risk factor.

The study consisted of data from 3,383 adolescents between the ages of 12 and 19, who were part of the National Health and Nutrition Examination Survey from 1999 to 2008.

While there was dramatic increase in diabetes rates, researchers found no increase in levels of obesity, high blood pressure or bad cholesterol from 1999 to 2008.

About 26 percent of teens who were overweight or obese with prehypertension or hypertension as well as borderline or high LDL or “bad” cholesterol, a percentage that hasn’t fluctuated significantly since 1999, according to researchers.

Experts are still unsure as to why the proportion of teens with high blood sugar would increase, while the rates of other heart disease risk factors, like weight and hypertension and cholesterol, stayed the same.

However, the swing in diabetes results could have something to do with the test researchers used to measure blood sugar, said Dr. Stephen Daniels, a University of Colorado School of Medicine expert who was not involved in the study, according to the Associated Press.

The tests given to adolescents in the study can give varying results, depending on the day or time of the day the tests is conducted, and other more comprehensive and expensive tests may be more precise. 

Daniels told AP that another testing method may not have produced such a dramatic rise in diabetes rates. 

"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," lead author Ashleigh May, a CDC epidemiologist said to AP.

Another study presented at the Heart Failure Congress 2012, a main annual meeting of the Heart Failure Association of the European Society of Cardiology, in Belgrade, Serbia found that while obese adolescents generally have no symptoms of heart disease, they already show signs of heart damage.

Previous studies have found structural and functional changes in the hearts of obese adults, but the latest study found a link between body mass index (BMI) and cardiac function in overweight and obese adolescents with no symptoms of heart disease.

Researchers found that the thickness of the interventricular septal, left ventricular posterior wall and left ventricular mass index increased with BMI.

 While the left ventricular early diastolic lateral, septal and systolic velocities were only reduced in obese adolescents and not in overweight adolescents, researchers found a significant association between these parts of heart function and BMI.

Researchers concluded that while obese adolescents had no symptoms of heart disease, they had damaged hearts and thicker walls, and impaired systolic and diastolic function of their hearts.

They explained that because both the structural and functional measures correlated with BMI, the latest findings may explain why obesity is a risk factor for potential heart disease. 

"Education on healthy food and exercise is needed in schools to prevent obesity and early cardiovascular disease in adolescents," says lead author Professor Gani Bajraktari, at the University of Pristina in Kosovo in a statement. "This is an important step in preventing obesity and cardiovascular disease in adults."