The worldwide rise among youth of obesity presages a likely progression to the metabolic syndrome in countless children and adolescents. Risk assessment in youth has hitherto been hampered because definitions of the metabolic syndrome apply to adults and may be inappropriate. This consensus report from the International Diabetes Federation seeks to remedy this situation by providing a definition that could be used to identify youngsters at risk.

Energy-rich diets and sedentary lifestyles are driving the worldwide rise in prevalence of childhood obesity. The World Health Organization reported in 2004 that an estimated 22 million adolescents and children under five years of age, and one in ten of school-aged children (5-17) were overweight or obese. This increase in prevalence is set to continue in both the developed and developing countries, and it is estimated that over 2 million adolescents in the USA currently have metabolic syndrome, which is likely to progress to type 2 diabetes and cardiovascular disease in later life.

Risk factors for the metabolic syndrome among children

Various factors contribute to a child’s future level of risk of developing the metabolic syndrome, including genetic background, low birth weight, maternal gestational diabetes, infant feeding practices, socioeconomic factors, and being raised in an “obesogenic” environment.

Components of new definition of the metabolic syndrome

The purpose of the new International Diabetes Federation (IDF) definition in children and adolescents is to provide a clinically accessible diagnostic tool to identify those at risk.
Data, albeit limited, from published studies in youth were used to define new criteria, which are to be viewed as a starting point, to be modified as new findings become available.

The new IDF definition is divided according to age range: 6 to <10, 10 to <16, and 16 years. Abdominal obesity is taken as the sine qua non in all three age groups. Below age 10, it is suggested that the metabolic syndrome as an entity should not be diagnosed, but the need for weight reduction should be stressed. Above age 10, the metabolic syndrome can be diagnosed, on the basis of abdominal obesity plus two or more other components (elevated plasma glucose, hypertension, low high-density lipoprotein (HDL)-cholesterol, elevated triglycerides). IDF adult criteria can be used for adolescents aged 16 and over, and a modified version of these criteria is to be applied to children aged 10 to <16.

* Mandatory criterion

Proposed IDF definition of the metabolic syndrome in children and adolescents

Abdominal obesity as sine qua non

Waist circumference in children is an independent predictor of blood pressure, insulin resistance, and lipid levels, all of which are components of the metabolic syndrome. Insulin sensitivity is lower in obese youth with a high waist/hip ratio, and decreases with increasing waist circumference percentiles. Together with incontrovertible evidence of the dangers of obesity in adulthood, these findings justify the use of abdominal obesity as an indispensable condition for the diagnosis of metabolic syndrome in children and adolescents.

In view of a lack of consistency regarding cutoff points for other components of the metabolic syndrome (triglycerides, HDL-cholesterol, blood pressure, fasting glucose), the new IDF definition uses adult values.

The way forward

The authors recommend various topics for future study, including: 1) the relation between body fat and its distribution in children and adolescents; 2) links between early growth patterns and future adiposity, metabolic syndrome, diabetes, and cardiovascular disease; 3) the definition of obesity in children; 4) long-term follow-up of children and adolescents to determine the effectiveness of intervention strategies such as lifestyle modification.

Zimmet P, Alberti KGMM, Kaufman F, et al. The metabolic syndrome in children and adolescents – an IDF consensus report. Pediatric Diabetes 2007;8:299-306