Two-thirds of severely obese children are at risk for heart disease, according to a new Danish study.

Of the 255 severely obese children in the study, 56 percent had high blood pressure, 54 percent had high cholesterol levels, 14 percent had high fasting blood glucose(a risk factor for diabetes), and 1 percent had Type 2 diabetes.

In total, 67 percent had at least one risk factor for heart disease, 17 percent had two risk factors, and 2.5 percent had four or more.

The percentage of kids in the study with high levels of blood sugar, an indicator for diabetes, "is worrying, considering the increasing prevalence worldwide of Type 2 diabetes in children and adolescents," the researchers wrote.

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

In the study, the researchers asked pediatricians for data on all severely obese children they treated between 2005 and 2007. Children were considered to be severely obese at age 2 if their body mass index (BMI) was 20.5, at age 12 if their BMI was 31, and at age 18 if their BMI was 35. The doctors provided data on each child's risk factors for heart disease.

Severely obese children under age 12 were nearly as likely as older children to have one or more risk factors for heart disease, the study found. Sixty-two percent of these younger children had at least one risk factor.

Only one child in the study was overweight due to a medical cause (hypothalamic tumor); the rest were obese due to their lifestyle, according to the study.

A study conducted in the U.S. between 1999 to 2004 found that 4 percent of U.S. children between ages 2 and 19 were severely obese. Another study found that 84 percent of severely obese U.S. children (between ages 5 and 17) had one or more risk factors for cardiovascular disease, the researchers pointed out.