Medical researchers say imaging tests on obese children as young as eight years old have revealed evidence of significant heart disease.

Thickening of heart muscles and increased muscle mass in the left ventricle, both known signs of heart disease, could increase the risk of obese children facing early death as adults, the researchers say.

"This was surprising and alarming to us," says study lead author Linyuan Jing of the Geisinger Health System in Danville, Penn.

"At such a young age, [children have] already developed clear evidence of heart disease," says Jing, explaining the findings presented at a gathering of the American Heart Association in Florida.

For the study, the researchers used magnetic imaging and other diagnostic tests on 40 children in Kentucky, half of whom were normal weight, while the other half were classified as clinically obese.

A significant number of the obese children, who ranged in age from 16 down to as young as eight, were found to have early signs of abnormalities of the heart muscles.

On average, the obese children had 27 percent more muscle mass in the heart's left ventricle, and their overall heart muscle was 12 percent thicker compared with the children of normal weight, the researchers report.

Thickened heart muscle reduces the heart's ability to pump blood, they say, and this reduction in capacity could put the obese children at "high risk" for cardiac strain and heart disease upon reaching adulthood.

While physical symptoms of heart disease were not seen in any of the obese children in the study — and the researchers pointed out that not all the obese children showed signs of heart issues — they warn that heart problems in childhood can often lead to more serious health conditions during adulthood.

"Ultimately we hope that the effects we see in the hearts of these children are reversible; however, it is possible that there could be permanent damage," Jing says. "This should be further motivation for parents to help children lead a healthy lifestyle."

In addition to signs of heart disease, some of the children in the study had other conditions linked to obesity, including elevated blood pressure, asthma and depression, the researchers reported.

Obesity is seen as a growing concern among the young; it is estimated one in three children between the age of two and 19 is overweight or diagnosed as clinically obese.

"This implies that obese children even younger than 8 years old likely have signs of heart disease too," Jing says. "This was alarming to us. Understanding the long-term ramifications of this will be critical as we deal with the impact of the pediatric obesity epidemic."