A study of very obese children suggests half may have a worrisome cluster of health conditions that increase their risk of developing diabetes and heart disease at an early age.

Researchers at Yale University School of Medicine said their findings suggested that this combination of health ills, a condition called metabolic syndrome, was more common among children and adolescents than previously thought and increased with the level of obesity.

“Obesity is not just a cosmetic issue. It’s a big problem because you open the door for serious, chronic complications,” said Dr. Sonia Caprio, who runs a pediatric obesity clinic at Yale.

Caprio said metabolic syndrome increased these youngsters’ risk of early development of type 2 diabetes and heart disease — problems usually associated with middle age.

Within two years, eight of 34 children with metabolic syndrome developed type 2 diabetes, according to the study in today’s New England Journal of Medicine.

“This is a yellow flag and a warning for public health officials and education systems to focus on reducing childhood obesity,” said Dr. Sethu Reddy, an endocrinologist at The Cleveland Clinic.

The conditions generally used to define metabolic syndrome are obesity, high blood pressure, high blood sugar, high triglycerides and low HDL, the good form of cholesterol. Anyone with three of the five conditions is considered to have metabolic syndrome, and about a quarter of adults have it.

The researchers tested 439 children and adolescents — 244 who were moderately obese and 195 severely obese. Also tested were 51 of their siblings who were overweight or lean.

Metabolic syndrome was found in 50 percent of the severely obese and 39 percent of the moderately obese but not in any of their siblings.