Two out of three severely overweight youngsters have risk factors for heart disease. (Reuters)

As many as two out of three children classified as very obese already have risk factors for heart disease, a new Dutch study warns.

The research, which aims to display the scale of underlying health problems among an increasingly overweight youth, found that several obese youngsters were already suffering from high blood pressure, which would normally only be found in adults.

Published in the journal Archives of Disease in Childhood, the study was carried out by researchers in Amsterdam, who based their findings on data supplied by paediatricians to the Dutch Paediatric Surveillance Unit between 2005 and 2007.

Throughout this period, doctors treating all new cases of severe obesity in children aged two to 18 across the Netherlands supplied information on their patients' cardiovascular risk factors.

Over the three years, information on 500 children was collated every month. When paediatricians were contacted again, with a request for further data, 363 responded, with 307 of the children being correctly classified as severely obese.

Of these, two-thirds had a least one cardiovascular risk factor, while 57 percent were found to have high blood pressure. Just over half had high levels of "bad" cholesterol, and one in every seven had high fasting blood glucose. Just over 1 percent already had type 2 diabetes.

Almost two-thirds of children in the sample under 12 had one or more cardiovascular risk factor, while only one child's obesity was attributable to medical rather than lifestyle factors.

"The prevalence of impaired fasting glucose in [these children] is worrying, considering the increasing prevalence worldwide of type 2 diabetes in children and adolescents," the authors commented.

"Likewise the high prevalence of hypertension and abnormal lipids may lead to cardiovascular disease in young adulthood."

They conclude: "Internationally accepted criteria for defining severe obesity and guidelines for early detection and treatment of severe obesity and [underlying ill health] are urgently needed."