Some obese children have the arteries of 45-year-old adults, according to scientists.
Researchers in the US used ultrasound to measure the thickness of arteries in the necks of 70 boys and girls with an average age of 13. They discovered that many had "furred-up" arteries looking like those of people 30 years older.
All the children had heart disease risk factors such as abnormal levels of cholesterol and triglyceride blood fats, or raised blood pressure. And more than half had a body mass index (BMI) - a measurement relating height and weight - in the top 5% of the population.
The ultrasound tests determined the intima-media thickness of the carotid arteries which carry blood to the brain. Known as CIMT, this shows the width of the inner walls of the artery, which can become "furred up" by fatty deposits.
Arteries narrowed by fatty plaques can lead to strokes and heart attacks.
Study leader Dr Geether Raghuveer, from the University of Missouri Kansas City School of Medicine, said: "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. 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."
The children's average CIMT was 0.45 millimetres, with a maximum of 0.75 millimetres. Their "vascular age", as reflected in the state of their arteries, was about 30 years older than their actual age, Dr Raghuveer said.
Because of obesity, abnormal heart disease, and/or a family history of heart disease, they were considered at high risk for future heart trouble. Higher BMI and higher systolic blood pressure - the pressure that coincides with each heart beat - both had a big impact on the children's arteries. Of all the risk factors, high triglycerides levels were most associated with prematurely ageing blood vessels.
A total of 38 children with high triglycerides had a carotid thickness in the top 75% for 45-year-olds. Those with lower triglycerides were evenly divided between the top 75% and bottom 25%.
"Vascular age was advanced the furthest in the children with obesity and high triglyceride levels, so the combination of obesity and high triglycerides should be a red flag to the doctor that a child is at high risk of heart disease," Dr Raghuveer said.