A Comparative Study of Reference Data for Body Mass index of School children in Shiraz (Southern Iran) and CDC Standards

Background: Several methods have been used to estimate adiposity with high precision, but BMI has become the most common marker in identifying overweight and obese subjects. This study was performed to present reference data for body mass index (BMI) of school children aged 6.5-11.5 years in Shiraz, southern Iran. Methods: The data of present study are based on a random multi stage sample survey of 2397 healthy school children in Shiraz, southern Iran. The participants were 1268 boys and 1129 girls and their heights and weights were measured in 2002-2003 academic year. Joint height-weight measurements were available for 2195 (91.6%) including 1138 boys (89.7%) and 1057 girls (93.6%). Healy-Rasbash-Yang (HRY) distribution-free method was applied to estimate BMI age-related centiles. Results: Cubic polynomials in age are shown to adequately fit the BMI data (on log scale). Children are now heavier than those born over ten years earlier. Boys BMI lie above girls to around 10 years of age, which is subsequently reversed for overweight and obese centiles. Conclusions: Comparison of these BMI curves with those of CDC charts showed substantial differences at every age and suggested the necessity for the use of locally based BMI norms for assessing body mass index of children in Shiraz, Southern Iran. Also, a positive secular trend in BMI is seen during the past decade in Iran.