ORIGINAL ARTICLE Obesity among Children Residing in Mexico City and its Impact on Lung Function: A Comparison with Mexican-Americans Rogelio Pe ´rez-Padilla, a Rosalba Rojas, c Victor Torres, b Victor Borja-Aburto, b and Gustavo Olaiz c (and the EMPECE Working Group) 1 a Instituto Nacional de Enfermedades Respiratorias, Mexico, D.F., Mexico b Instituto Mexicano del Seguro Social, Coordinacio ´n de Salud en el Trabajo, Mexico, D.F., Mexico c Instituto Nacional de Salud Pu ´blica, Mexico, D.F., Mexico Received for publication March 14, 2005; accepted May 3, 2005 (ARCMED-D-05-00100). Background. The objective of the study was to describe the prevalence of obesity among Mexican children and its impact on ventilatory lung function. Methods. We studied cross-sectionally 6784 students between 8 and 20 years of age attending schools located !2 km away from ten air pollution monitors located throughout metropolitan Mexico City. The comparison group was made up of 1924 Mexican-Americans of the same age, studied during the NHANES-III examination, which included information on spirometry and body mass index (BMI). Results. Of all our subjects, 9.7% had a BMI O95 th percentile of CDC growth charts (compared to 15.1% in Mexican-Americans) and 6.6% fulfilled the obesity criteria of the International Obesity Task Force (vs. 12.2%). Obesity was related to male gender, asthma and passive smoking. At the same height and gender, lung function was higher in Mexicans than in Mexican-Americans, perhaps due to altitude. In children 8–11 years of age, lung function increased in heavier subjects but, in older children and youths, function reached a plateau and decreased among children with highest BMI (inverted U pattern, seen in adults). Conclusions. Obesity is higher in Mexican-American children and youths than in Mexicans. Spirometric function is affected adversely by obesity, especially in young people. Ó 2006 IMSS. Published by Elsevier Inc. Key Words: Body mass index, Obesity, Spirometry, Lung function, Undernourishment, NHANES III, Altitude, Mexico, Mexican-Americans. Introduction Obesity is a growing risk for disease in the world (1), present even in developing countries still affected by malnutrition. However, the many definitions of obesity currently in use make it difficult to compare countries and secular trends (2). Recently, new criteria for obesity were proposed by the Centers for Disease Control and Prevention (CDC) (3) and also by the International Obesity Task Force (IOTF); the latter based on pooled international data (4). Extreme levels of obesity have been associated with reduced lung function (5). In addition, lung function improves after weight loss in cases of obesity (6,7) and drops after weight gain associated with the cessation of smoking (8). Impairment of lung function with obesity has also been described in children and adolescents (9), but data, especially population-based, are scarce. The purpose of our work was to describe the prevalence of obesity and undernourishment in students from metropolitan Mexico City and the pattern of impact on pulmonary function compared to Mexican-Americans. Address reprint requests to: Rogelio Pe ´rez-Padilla, M.D., Instituto Nacional de Enfermedades Respiratorias, Tlalpan 4502, Me ´xico DF, Me ´xico; E-mail: perezpad@servidor.unam.mx 1 The EMPECE working group also includes Margarita Rojas, a Minerva Catala ´n SW, a Rocı ´o Chapela, a Jaime Villalba-Caloca, a Isabelle Romieu, c Laura Mendoza, c Teresa Fortoul, and Justino Regalado. a 0188-4409/06 $–see front matter. Copyright Ó 2006 IMSS. Published by Elsevier Inc. doi: 10.1016/j.arcmed.2005.05.009 Archives of Medical Research 37 (2006) 165–171