Two out of three severely obese kids already have at least one risk factor for heart disease, suggests research published online in Archives of Disease in Childhood.

The prevalence and severity of childhood obesity has been rising worldwide, but little research has been carried out on the underlying health problems that children with severe weight problems have, say the authors.

They base their findings on data supplied by pediatricians to the Dutch Paediatric Surveillance Unit between 2005 and 2007.

During this period, doctors treating all new cases of severe obesity in children from the ages of 2 to 18 across The Netherlands were asked to supply information on their patients' cardiovascular risk factors, including high blood pressure, fasting blood glucose levels, and blood fats (lipids).

The definition of severe obesity started at a body mass index (BMI) of 20.5 for a 2 year old, at 31 for a 12 year old, and at 35 for an 18 year old.

Over the three years, most (87% to 94%) of pediatricians submitted their monthly findings on every severely obese child they treated to the surveillance unit, providing information on 500 children in all.

When pediatricians were contacted again, with a request for further data, 363 responded and 307 of their children were correctly classified as severely obese.

Just over half (52%) of these 307 children were boys. They tended to be more severely obese at the younger end of the age spectrum; the reverse was true of girls. Full information on cardiovascular risk factors was available for 255 (83%).

Two out of three (67%) had at least one cardiovascular risk factor. Over half (56%) had high blood pressure; a similar proportion (54%) had high levels of low density 'bad' cholesterol; one in seven (14%) had high fasting blood glucose; and just under 1 per cent already had type 2 diabetes.

And "remarkably" say the authors, almost two thirds (62%) of those aged 12 and under had one or more cardiovascular risk factors. Only one child's obesity was attributable to medical rather than lifestyle factors.

Nearly one in three severely obese children came from one parent families.

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

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

And 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."