Childhood obesity in the United States has skyrocketed over the past 30 years, according to the CDC. (Trent Penny-The Anniston Star via AP)

The imaging tests left little room for doubt. They showed thickened heart muscles and increased muscle mass in the left ventricle — both signs of heart disease. But the troubling scans didn't belong to ailing adults. They belonged to obese children, some as young as 8.

"This was surprising and alarming to us," said Linyuan Jing, the lead author behind new findings being presented this week at an American Heart Association gathering in Florida. "At such a young age, [children have] already developed clear evidence of heart disease."

The study focused on 40 children in Kentucky, half of whom were considered normal weight and the other half clinically obese. Using magnetic resonance imaging, among other tests, researchers found that a striking number of the obese children — who ranged in age from 8 to 18 — showed early signs of heart muscle abnormalities. Some actually showed early signs of impaired heart function.

[How obesity harms a child's body]

Health experts have long warned that obesity during childhood can lead to an array of problems later in life, including heightened risk for heart attacks and stroke. But the results of the Kentucky study offer new evidence about just how early damage can begin. "We did not expect to see heart disease at such an early age," said Jing, now a cardiac researcher at the Geisinger Health System in Pennsylvania.

Researchers tried to account for other factors that could have contributed to the early signs of trouble, she said. They excluded children with genetic heart problems, diabetes or other conditions.

Jing acknowledged that plenty more work lies ahead to determine what's driving the cardiac changes in obese children and whether they can be reversed over time. While early heart damage showed up in many of the kids in the study, about 40 percent had no signs of heart disease.  She said that larger studies are necessary to examine the long-term implications.

"This is only a preliminary study. ... We definitely want to confirm our findings in a larger, longitudinal study with more children," said Jing, who is helping to recruit 200 youths to follow over several years.

The study, funded in part by the National Institutes of Health, isn't the first to examine the effect of obesity on young hearts, said Stephen Daniels, chairman of the pediatrics department at the University of Colorado School of Medicine. Researchers have long used echocardiograms and other imaging techniques for similar efforts, and the notion that excess weight and high blood pressure can cause thickening of heart's left ventricle has been explored in previous studies.

[Fighting childhood obesity, one playground at a time]

But the study helps underscore how pervasive the problem is and why, he said.

"It reinforces the concept that obesity has negative impact on cardiovascular system and shows that it can happen at a young age," Daniels said. "We look at overweight kids, and for the most part, they seem healthy and don’t feel bad. But beneath the surface, there are things going on that are not good for their health."

The Centers for Disease Control and Prevention estimates that the percentage of obese children under 11 has more than doubled in the past three decades, to nearly one in five. The statistics for teenagers are even more grim: from 5 percent in 1980 to nearly 21 percent by 2012.

Beyond increased risk for cardiovascular problems, obese children also are more likely to develop Type 2 diabetes, and they are at greater risk for bone and joint problems, sleep apnea and an array of psychological and social issues.

This post has been updated. 

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