"There's a saying that 'you're as old as your arteries,' meaning that the state of your arteries is more important than your actual age in the evolution of heart disease and stroke," said Geetha Raghuveer, professor of pediatrics at the University of Missouri School of Medicine and cardiologist at Children's Mercy Hospital, Kansas City, Kansas.
"We found that the state of the arteries in these children is more typical of a 45-year-old than of someone their own age," she said.
Researchers, who presented their work at the American Heart Association's Scientific Sessions 2008 in New Orleans, used ultrasound to measure the thickness of neck arteries - carotid arteries - that supply blood from the heart to the brain.
Increased carotid artery intima-media thickness indicates a fatty buildup of plaque, which can clog the arteries and lead to a heart attack or stroke.
Researchers analyzed data from 34 boys and 36 girls who were deemed "at-risk" due to obesity, abnormal cholesterol and/or a family history of early heart disease.
The group's average age was 13 and 89 percent of the participants were white.
It was discovered the children's "vascular age" - the age at which the level of artery thickening would be normal for their gender and race - was approximately 30 years older than their actual age, Raghuveer said.
Researchers also found that having a higher Body Mass Index and higher blood pressure had the biggest impact on CIMT.
Further research is needed to determine whether the build-up of artery thickness decreases if children lose weight and exercise, according to the study.
"I'm optimistic that something can be done," Raghuveer said.
"In children, the buildup in the vessels is not hardened and calcified. We can improve the vessel walls and blood flow in adults through treatment, and I'm sure we can help children even more."