ABC | Volume 114, Nº3, March 2020

Original Article Santos et al. Waist circumference of children in Brazil Arq Bras Cardiol. 2020; 114(3):530-537 hypertension. It has been suggested that WC measurement could replace BMI in risk assessment for obesity-related comorbidities among young populations. 4-7 Since WC values are influenced by age, gender, ethnic and geopolitical differences, available studies have presented the distribution of WC percentiles of children and adolescents of a wide range of countries. 8-29 Based on the above-mentioned, we intended to boost the set of information already reported by some national studies on this matter 30-37 by describing the WC percentile distribution and by calculating the WC cut‑off values which would be able to predict obesity in a large sample of children aged from 6 to 10 years in the São Paulo State. Moreover, we compared the current WC percentile with data obtained from studies performed in other countries and another Brazilian study evaluating a similar population, according to age and gender. Methods Design and study population This is a longitudinal, prospective, multicenter study, initiated in March 2010 and concluded in July 2010. The study was scientifically supported by the São Paulo Society of Cardiology (Sociedade de Cardiologia do Estado de São Paulo, SOCESP), and was regionally coordinated by the SOCESP Regional Directory Office of Araras, SP. The current study aimed to include at least 30% of children of both genders, aged from 6 to 10 years old, enrolled at public and private elementary schools of the 13 cities of the Araras District of São Paulo State, Brazil. According to the Statistical and Educational Nationwide Survey Data provided by the National Institute of Educational Studies Anisio Teixeira (INEP), the number of children enrolled in all the cities included in the present study was 63,891 in 2010. In order to exclude children who did not attend school and special needs students older than 10 years of age (which would go beyond the age limit of this study) we used a correction factor of 10% of the total sample. Thus, the total estimated population of children from 6 to 10 years old was 57,501 in these localities. The Secretariats of Education and the municipal and private schools of all Municipalities were contacted. The study was carried out in places where there was an approval in all instances: 147 public schools and 14 private schools. The Schools' coordination and parent’s permission to participate in the evaluation was duly secured and each participating center had to comply with the ethical and data management guidelines of the local institution. The children´s age was reported by Rousham et al. 38 study. Therefore, 15 June of the year birth was taken as an estimated date of birth. Anthropometry measurements and WC percentiles comparison Trained researchers performed the measurements according to standardized procedures. Anthropometric measurements were undertaken with the children wearing light clothing and no shoes. The height and weight was measured in duplicate with a digital electronic scale provided with a portable stadiometer, to the nearest 0.1 cm and 0.1 kg, respectively. The average of the two measurements was used to calculate the BMI [BMI = weight (kg)/height(cm) 2 ]. Boys and girls were classified according to the BMI percentile ranges (the BMI curves established for each gender and age), using the parameters of the population curves of NCHS-CDC (National Center for Health Statistics - Centers for Disease Control and Prevention - USA). 39 The nutritional state of the childrenwas categorized according to the BMI percentiles: obese (BMI > 95%), overweight (BMI between 85 and 95%) and normal weight (BMI < 85%). Abdominal circumference was measured in duplicate, at half the distance between the lowest rib and the superior border of the iliac crest, with a non-flexible tape, in the upright position, with the abdomen relaxed at the end of gentle expiration. 40 To compare the actual WC percentiles distribution, we performed a literature review of the population-based studies that had evaluated this parameter in a similar age group. For comparisons among countries, we used the 50 th percentiles of WC according to age. Our data has also been compared with a previous Brazilian study, to identify trends in abdominal circumference values in time. Statistical analysis Anthropometrical data from the pediatric population are presented as mean ± standard deviation (SD), median, percentiles and minimum and maximum values. The linear (Pearson’s correlation coefficient) or non-linear correlation (logarithmic, inverse, quadratic, cubic, compound, power, sigmoid, growth and exponential coefficient) was calculated by regression. If significant, the higher linear or non-linear coefficient was used to identify the best model which explains the phenomenon. To establish the WC best cut-off value for obesity diagnosis, we generated a ROC Curve with normal weight and obese children using the BMI percentiles, stratified by gender and age, and used the highest sum of sensitivity and specificity to set the cut-off point (Youden Index). 41 A p < 0.05 was considered significant. The data were analyzed using IBM SPSS Statistics for Windows, Version 23.0 from IBM Corp. Released in 2015. Armonk, NY, USA. Results A total of 22,000 children (11,199 boys and 10,886 girls) were included, which represents more than 30% of the estimated population, ranging from 1,606 to 2,610 boys and from 1,612 to 2,502 girls for each of the five periods of age, from 6 to 10 years old. The mean baseline anthropometric characteristics separated by age and gender are presented in Table 1. There was an expected progressive increase in weight, height, BMI and WC in both genders from 6 to 10 years. The prevalence of obesity in each age group varied from a minimum of 17 % (6 years old) to a maximum of 21.6% (9 years old) among boys, and a minimum of 14.1% (7 years old) to a maximum of 17.3 % (9 years old) among girls (Table 1). Approximately 30% of boys and girls had excess of fat, and were classified as either overweight or obese. 531