Almost two out of three severely obese children under the age of 12 have at least one risk factor for heart disease such as high blood pressure or high blood sugar, researchers have said.
Dutch researchers found that 62% of very obese children aged 12 or younger have one or more of the risk factors.
The study, published online in Archives Of Disease In Childhood, examined 255 severely obese children aged between two and 18.
Overall, 67% of the children had at least one risk factor for heart disease. Almost one in five severely obese children have at least two risk factors and 8% were found to have three.
The most common risk factor was hypertension - or high blood pressure - which was present in 56% of the children. More than half had low levels of "good" cholesterol, while 14% of the overweight children had high blood sugar. Just under 1% already had type 2 diabetes.
The authors, from VU University Medical Centre in Amsterdam, based their findings on data supplied by paediatricians to the Dutch Paediatric Surveillance Unit between 2005 and 2007.
The authors found that younger boys were more often severely obese compared to older boys, while they found the reverse for girls. Nearly one in three severely obese children came from one-parent families.
The authors wrote: "Internationally accepted criteria for defining severe obesity and guidelines for the early detection and treatment of severe obesity and comorbidity are urgently needed."
British Heart Foundation senior cardiac nurse Doireann Maddock said: "Although it was a small study, the findings leave a bad taste in the mouth. It's a huge concern so many obese children were identified as already having at least one risk factor for heart disease, including high blood pressure, high blood glucose and problems with cholesterol levels.
"However, this is a problem that can be addressed by stopping young people becoming overweight and obese in the first place. Highlighting the importance of healthy eating and physical activity from an early age will help protect the heart health of future generations."