Diagnostic in Obesity and Complications Defining overweight and obesity in pre-school children: IOTF reference or WHO standard? L. Monasta 1 , T. Lobstein 2 , T. J. Cole 3 , J. Vignerová 4 and A. Cattaneo 5 1 Epidemiology and Biostatistics, Institute for Maternal and Child Health IRCCS Burlo Garofolo, Trieste, Italy; 2 International Association for the Study of Obesity, London, UK; 3 MRC Centre of Epidemiology for Child Health, UCL Institute of Child Health, London, UK; 4 Department of Children and Adolescents, National Institute of Public Health, Prague, Czech Republic; 5 Health Services Research, Epidemiology and International Health, Institute for Maternal and Child Health IRCCS Burlo Garofolo, Trieste, Italy Received 25 January 2010; revised 5 March 2010; accepted 9 March 2010 Address for correspondence: L Monasta, Epidemiology and Biostatistics, Institute for Maternal and Child Health IRCCS Burlo Garofolo, Via dell’Istria 65/1, 34137 Trieste, Italy. E-mail: monasta@burlo.trieste.it Summary Two international datasets are used to define overweight and obesity in pre-school children: the International Obesity Task Force (IOTF) reference and the WHO standard. This study compares the performance of the two datasets in defining overweight and obesity in 24–60 months old children. This was done by plotting the IOTF cut-offs against WHO curves and by comparing the prevalence of overweight and obesity, as defined by the IOTF reference and by the WHO standard, using 2001 data from the Czech Republic. The IOTF cut-off for over- weight in 24–60 months old children goes from 1.7 to 1.1 z-scores on the WHO chart, and for obesity it shifts with age from 2.7 to 2.2 z-scores. As a consequence, at 5 years of age the prevalence of overweight in Czech girls is 3.4% using the WHO and 15.3% using the IOTF definition. These discrepancies are due to the choice of cut-offs and to the different criteria used to select the sample for the IOTF reference and the WHO standard. Research is urgently needed to identify, for the WHO standard, BMI cut-offs associated with an increased risk of overweight and obesity, and associated health outcomes later in life. Keywords: Cut-offs, obesity, overweight, pre-school children. obesity reviews (2010) Introduction Overweight and obesity in children are a growing problem worldwide (1,2). Increasing attention is being given to obesity in children under 5 years of age (3,4). Two inter- national datasets are used to define overweight and obesity in pre-school children in terms of body mass index (BMI): the International Obesity Task Force (IOTF) reference and the WHO standard. The former, used for children and adolescents 2–18 years old, was developed from a database of 97 876 boys and 94 851 girls from birth to 25 years from six countries (Brazil, Great Britain, Hong Kong, the Netherlands, Singapore and the USA) (5). Centile curves were constructed using the LMS method (6), and BMI values of 25 and 30 at 18 years of age for boys and girls were tracked back to define BMI values for overweight and obesity at younger ages. The WHO standard is used for children 0–59 months of age and is based on a sample of 888 (longitudinal sample, birth to 24 months) plus 6697 (cross-sectional sample, 18–71 months of age) healthy breastfed infants and young children raised in environ- ments that do not constrain growth (7,8). The sample includes infants and young children from sites in six countries (Brazil, Ghana, India, Norway, Oman and the USA). Despite some discussion, there is general agreement on the appropriateness of BMI to define overweight and obesity and on the need to replace national reference curves with an international standard (9–11). However, during a review on the prevalence of overweight and obesity in obesity reviews doi: 10.1111/j.1467-789X.2010.00748.x 1 © 2010 The Authors Journal compilation © 2010 International Association for the Study of Obesity. obesity reviews