Incidence of obesity and its predictors in children and adolescents in 10 years of follow up: Tehran lipid and glucose study (TLGS)

BACKGROUND: Childhood obesity is one of the most challenging public health issues of twenty-first century. While we know that there is an increase in prevalence of childhood and adolescence obesity, incidence studies must be carried out. The main objective of this study was to determine childhood obesity incidence and its potential predictors in Tehranian urban population. METHODS: This study was conducted within the framework of the Tehran Lipid and Glucose Study (TLGS), addressing incidence and risk factors of obesity throughout several phases from 1999–2001 to 2009–2011 among Tehranian urban population. Total study subjects were 1033 non-obese children, aged between 7 to 11 years, with a median 8.7 years of follow-up. Body mass Index (BMI) was used to define obesity and overweight based on World Health Organization (WHO) criteria, and definition of metabolic syndrome (MetS) for children was based on the Cook survey. Cumulative incidence of obesity and obesity incidence rates were calculated for each gender. Cox proportional hazard models was used to estimate potential risk factors of obesity. RESULTS: Our Participants had a mean age of 9.2 ± 1.4 years, mean BMI of 16.1 ± 2.2 kg/m(2) and mean waist circumference (WC) of 57.2 ± 6.7 at baseline. Total cumulative incidence of obesity was calculated to be 17%, CI =14.1–20.4 for whole population (19.6%, CI =15.4–24.8 for boys and 14.5%,CI = 10.9–19.1 for girls). Participants which were in the age group of 7–9 years at baseline experienced higher rate of cumulative obesity incidence compared to those who were in the age group of 10–11 years at baseline (22% vs 10.8%). In addressing risk factors, 5 parameters were significantly associated with obesity incidence: being overweight at baseline (HR = 14.93 95%CI: 9.82–22.70), having higher WC (HR = 5.05 95%CI: 3.01–8.48), suffering from childhood MetS (HR: 2.77 95%CI: 1.57–4.89) and having a obese father (HR: 2.69 95%CI: 1.61–4.50) or mother (HR: 3.04 95%CI: 1.96–4.72). CONCLUSION: Incidence of obesity is significantly high in Tehranian children, especially the age group 7–9 years. Best predictors of childhood obesity incidence are childhood overweight, WC above 90th percentile, childhood MetS and parental obesity.