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Obese children as young as 10 have the arteries of 45-year-olds and other heart abnormalities greatly increasing their risk of heart disease, say doctors who have used ultrasound tests to take a peek inside.

"As the old saying goes, you're as old as your arteries are," said Dr Geetha Raghuveer of Children's Hospital in Kansas City, who led one of the studies. "This is a wake-up call."

The studies, reported yesterday at an American Heart Association conference, found about a third of United States children are overweight and one-fifth are obese.

Many parents think "baby fat" will melt away as children get older. But research increasingly shows fat children become fat adults, with higher risks for many health problems.

"Obesity is not benign in children and adolescents," said Dr Robert Eckel, a former heart association president and cardiologist at the University of Colorado-Denver.

The American Academy of Pediatrics recently recommended cholesterol-lowering drugs for some children, he noted.

Dr Raghuveer wanted to see if early signs of damage could be documented. She and colleagues used ultrasound to measure the thickness of the wall of a major neck artery in 70 children, ages 10 to 16. Almost all had abnormal cholesterol and many were obese.

No one knows precisely how thick a 10-year-old's artery should be, since they're not regularly checked for signs of heart disease, but doctors do know that they should not look like those of people much older and larger.

Researchers used tables for 45-year-olds, who often do get such exams, found the kids' "vascular age" was about 30 years older than their actual age.

A separate study tied childhood obesity to abnormal enlargement of one of the chambers of the heart. Enlargement is a known risk factor for heart disease, stroke and heart rhythm problems.

Julian Ayer, a researcher at Royal Prince Alfred Hospital in Sydney, did ultrasound exams on 991 seemingly healthy children ages 5 to 15. He saw a clear link between rising weight and size of the left atrium.

A study by Dr Walter Abhayaratna, of Australian National University in Canberra, found impairment in the heart's ability to relax between beats in children who were overweight or obese.

The study involved the first 150 children participating in a larger community-based study.

Earlier research he helped to conduct found more rigid arteries in such children - a possible sign of plaque deposits starting to form.

"Even at this young age of 10, you can have children who have got arterial stiffness who are comparable to 30- and 40-year-olds," he said.

Dr Michael Schloss, a New York University heart disease prevention specialist, said the evidence showed obesity was more than a cosmetic issue for kids.

"If you've seen what's on the menu for most school lunches, these findings are no surprise," he said.

"The time has come to seriously deal with the issue of childhood obesity and physical inactivity on a governmental and parental level."

- AP