Fernanda Garcia-Villanueva, 8, takes her pulse at a group exercise session in the 10-week Shapedown Program at The Children's Hospital in Aurora, Colorado May 29, 2010. Getty Images/Rick Wilking Children as young as eight-years-old in the US are showing strong signs of heart disease as a consequence of obesity.

A review comparing 20 obese children with the same number of children of normal weight found that obesity was tied to 27% more muscle mass in the heart's left ventricle, and heart muscles were 12% thicker – typical traits of heart disease.

As a result, the researchers found that 40% of children were considered "high-risk" because of the impaired pumping ability of the heart.

None of the children involved in the study showed any physical symptoms due to the fact that they still have age on their side, but the researchers warn that the damage early on may be irreversible and could lead to complications in adulthood.

Linyuan Jing, lead study author and a researcher at Geisinger Health System in Danville, Pennsylvania, said: "Parents should be highly motivated to help their children maintain a healthy weight.

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. This should be further motivation for parents to help children lead a healthy lifestyle."

The team warn that the number of children with heart disease may be underestimated due to the fact that their research excluded diabetic children and kids who were too large to fit in the magnetic resonance imaging machine which was used to detail the heart.

"As a result, this means the actual burden of heart disease in obese children may have been ­under­-estimated in our study because the largest kids who may have been the most severely affected could not be enrolled," Jing said.

One in three children aged between two and 19 in the United States are classified as overweight or clinically obese. Nonetheless, despite the prevalence of the problem, researchers didn't expect to see evidence of heart disease at such a young age.

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

The study was presented at the American Heart Association's Scientific Sessions 2015.