Children who are not obese or obviously overweight, but just a little podgy may be harming their hearts, a study says.
Only severely obese children were thought to be at risk
A team found excess fat in body tissue, known as adiposity, caused blood vessels to be less elastic - an early indication of cardiovascular disease.
Researchers at London's St George's Hospital Medical School concluded that even a little fat could increase the risk, the journal Circulation reported.
Heart experts said efforts needed to be made to alter children's lifestyles.
Obesity in adults is associated with a clustering of heart disease risk factors such as high blood pressure.
In the past these signs were uncommon in all but the most obese children.
But the researchers found childhood adiposity had a similar adverse effect, in their study of 500 children aged 13 to 15.
The team measured the elasticity of blood vessels by using ultrasound and testing blood pressure, insulin levels and skin-fold thickness - an indication of body mass and fat accumulation.
The team noted that the effects of adiposity on blood vessel elasticity occurred at "body mass index levels well below those considered to represent obesity".
Lead researcher Dr Peter Whincup said: "The impact of adiposity appeared stronger than previously documented association between cholesterol and blood vessel elasticity.
"These observations emphasise the importance of population-wide strategies to reduce childhood adiposity by a combination of changes in diet and physical activity."
Professor Peter Weissberg, medical director at the British Heart Foundation, said: "The study reinforces the message that the seeds of heart disease are sown in early life, which is why it is so important to try to alter the lifestyle of our children."