BACKGROUND: The World Health Organization (WHO) European Childhood Obesity Surveillance Initiative (COSI) was established more than 10 years ago to estimate prevalence and monitor changes in overweight and obesity in children aged 6-9 years. Since then, there have been five rounds of data collection in more than 40 countries involving more than half a million children. To date, no comparative studies with data on severe childhood obesity from European countries have been published. OBJECTIVES: The aim of this work was to present the prevalence of severe obesity in school-aged children from 21 countries participating in COSI. METHOD: The data are from cross-sectional studies in 21 European WHO member states that took part in the first three COSI rounds of data collection (2007/2008, 2009/2010, 2012/2013). School-aged children were measured using standardized instruments and methodology. Children were classified as severely obese using the definitions provided by WHO and the International Obesity Task Force (IOTF). Analyses overtime, by child's age and mother's educational level, were performed in a select group of countries. RESULTS: A total of 636,933 children were included in the analysis (323,648 boys and 313,285 girls). The prevalence of severe obesity varied greatly among countries, with higher values in Southern Europe. According to the WHO definition, severe obesity ranged from 1.0% in Swedish and Moldovan children (95% CI 0.7-1.3 and 0.7-1.5, respectively) to 5.5% (95% CI 4.9-6.1) in Maltese children. The prevalence was generally higher among boys compared to girls. The IOTF cut-offs lead to lower estimates, but confirm the differences among countries, and were more similar for both boys and girls. In many countries 1 in 4 obese children were severely obese. Applying the estimates of prevalence based on the WHO definition to the whole population of children aged 6-9 years in each country, around 398,000 children would be expected to be severely obese in the 21 European countries. The trend between 2007 and 2013 and the analysis by child's age did not show a clear pattern. Severe obesity was more common among children whose mother's educational level was lower. CONCLUSIONS: Severe obesity is a serious public health issue which affects a large number of children in Europe. Because of the impact on educational, health, social care, and economic systems, obesity needs to be addressed via a range of approaches from early prevention of overweight and obesity to treatment of those who need it.

Centre for Applied Obesity Research Leeds Beckett University Leeds United Kingdom

Centre for Disease Prevention and Control Riga Latvia

Department of Child Health and Development Division of Mental and Physical Health Norwegian Institute of Public Health Oslo Norway

Department of Food and Nutrition and Sport Science University of Gothenburg Gothenburg Sweden

Department of food studies Nutrition and Dietetics Uppsala University Uppsala Sweden

Department of Health and Inequality Division of Mental and Physical Health Norwegian Institute of Public Health Oslo Norway

Department of Nutrition and Dietetics Alexander Technological Educational Institute of Thessaloniki Thessaloniki Greece

Department of Preventive Medicine Lithuanian University of Health Sciences Kaunas Lithuania

Faculty of Sport University of Ljubljana Ljubljana Slovenia

Health Authority San Marino San Marino San Marino

Institute of Public Health of the Republic of Macedonia Skopje North Macedonia

Institute of Public Health Tirana Albania

Istituto Superiore di Sanità National Centre for Disease Prevention and Health Promotion Rome Italy

National Center of Public Health and Analyses Sofia Bulgaria

National Institute of Health Dr Ricardo Jorge Lisbon Portugal

National Institute of Pharmacy and Nutrition DG of Food and Nutrition Science Budapest Hungary

National Institute of Public Health Bucharest Romania

Obesity Management Centre Institute of Endocrinology Prague Czechia

Primary Health Care Floriana Malta

Public Health Department Hacettepe University Ankara Turkey

Semmelweis University Karoly Racz School of PhD Studies Budapest Hungary

Social Security Institute San Marino San Marino San Marino

Spanish Observatory of Nutrition and Study of Obesity Madrid Spain

State University of Medicine and Pharmacy Chișinău Moldova

Turkish Ministry of Health Ankara Turkey

University College Dublin Dublin Ireland

WHO European Office for the Prevention and Control of the NCDs Moscow Russian Federation

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