The age of the obesity onset is a very important factor for the development of metabolic complications and cardiovascular risk in children and adolescents with severe obesity.

Severe obesity defined as BMI value corresponding to an adult > 40 kg/m 2 affects 1-5% of children and adolescents in Europe. The purpose of this study was to assess the occurrence of cardiovascular risk factors in children and adolescents with severe obesity. The analysis included 140 patients (75 female) at the mean age of 14 ± 2.1 SD (range 10-18) years (all recruited in 4 regional reference centers in Poland). Severe obesity was defined as BMI > 35 kg/m 2 (children 6-14 years), and BMI > 40 kg/m 2 (> 14 years). Fasting plasma samples have been obtained in all patients, and OGTT was performed in all patients. The metabolic risk factors were defined as high blood pressure (BP > 90 percentile for height, age, and sex), HDL cholesterol < 1.03 mmol/L, TG ≥ 1.7 mmol/L, and hyperglycemic state (fasting blood glucose > 5.6 mmol/L, or blood glucose 120' after oral glucose load > 7.8 mmol/L). Additionally, the MetS z-score was calculated using Metabolic Syndrome Severity Calculator. One hundred twenty-four (89%) participants presented with high BP, 117 (84%) with abnormal lipid profile, and 26 with the hyperglycemic. Only 12 (9%) were free of metabolic complications. More than 60% of patients had more than one cardiovascular risk factor. The high BP was significantly associated with the severity of obesity (F = 9.9, p = 0.002). Patients with at least one metabolic complication presented with significantly younger age of the onset of obesity (the mean age of the patients with no overt obesity complications was 10 years, while the mean age of those who presented at least one was 4.7 ± 3.5 SD years (p = 0.002)). A significant positive association between in the value of the Mets BMI z-score with age was observed (R = 0.2, p < 0.05). There were no differences between girls and boys regarding Mets BMI z-score (1.7 ± 0.8 vs 1.7 ± 0.7, p = 0.8).Conclusions: The most common metabolic risk factor in children and adolescents with severe obesity was high BP. The most important factor determining presence of obesity complications, and thus the total metabolic risk, seems to be younger (< 5 years) age of onset of obesity. What is Known? • It is estimated that 1-5% of children and adolescents in Europe suffer from severe obesity corresponding to an adult BMI > 40 kg/m2, and it is the fastest growing subcategory of childhood obesity. • Children with severe obesity face substantial health risk that may persist into adulthood, encompassing chronic conditions, psychological disorders and premature mortality. What is new: • The most common complication is high BP that is significantly associated with the severity of obesity (BMI z-score), contrary to dyslipidemia and hyperglycemic state, which do not depend on BMI z-score value. • The most important factor determining presence of obesity complications, and thus the total metabolic risk, seems to be younger (< 5 years) age of onset of obesity.