ORIGINAL ARTICLE Tracking of overweight from early childhood to adolescence in cohorts born 1988 and 1994: overweight in a high birth weight population E Johannsson 1 , SA Arngrimsson 1 , I Thorsdottir 2 and T Sveinsson 3 1 Center for Sport and Health Sciences, Iceland University of Education, Laugarvatn, Iceland; 2 Unit for Nutrition Research, Landspitali-University Hospital and Department of Food Science, University of Iceland, Reykjavı´k, Iceland and 3 Department of Movement Science, University of Iceland, Reykjavik, Iceland Objective: To investigate the prevalence and tracking of overweight and obesity in childhood cohorts born 1988 and 1994 in a population of high birth weight. Subjects: Icelandic cohorts born in 1988 and 1994. Materials and methods: Out of 1328, 9- and 15-year-old children from 18 randomly selected schools all over Iceland, 934 participated (71%). Height and mass were measured by the investigators. Also, height and mass at birth, and at age 2.5, 6, 9, and 12 years, were collected from maternity wards and school health registers. Results: The prevalence of overweight children ranged from 10.1% for 2.5-year-olds to 18.7% for 9-year-olds. No difference was observed between the two cohorts or sex. The prevalence of obesity in the 1994 cohort (4.3%) was significantly higher (P ¼ 0.01) at age 6 years, compared to the 1988 cohort (1.1%). The children who were overweight at age 2.5 years were more likely to be overweight at age 6 (OR ¼ 12.2) and 9 years (OR ¼ 4.9), but not significantly at age 12 or 15 years, compared with normal weight 2.5-year-olds. Overweight children at age 6 or 9 years were much more likely (OR 10.4 and OR 18.6, respectively) to be overweight at age 15 years compared to their normal weight peers. Of overweight 6-year-olds, 51% were overweight at 15 years, and were about one-third of all overweight children at that age. The children that weighed above the 85th percentile at birth were more likely than the other children to be overweight at the age of 6 years (OR ¼ 1.8), 9 years (OR ¼ 2.1), and 15 (OR ¼ 2.0) years. Conclusion: The results show high prevalence of overweight and obesity even before the start of compulsory schooling. Approximately, 51% of overweight 6-year-olds were still overweight after puberty. Therefore, preschool overweight prevention, along with prevention at school age, seems to be of uttermost importance. International Journal of Obesity (2006) 30, 1265–1271. doi:10.1038/sj.ijo.0803253; published online 21 February 2006 Keywords: children; tracking; cohort; overweight and Iceland Introduction Trends indicating an increase in the proportion of over- weight and obese children and adolescents have been reported in numerous studies from different industrialized countries for the last two decades. 1–4 Obesity in childhood affects children’s health and well-being, and tracks into adulthood leading to serious consequences. 5–7 Moreover, the most recent studies from various parts of the world indicate that this trend seems to affect even preschool children aged 2–6 years. 8–12 Recently, more attention has been given in epidemiologi- cal studies to tracking, which is defined as the maintenance of relative position in the rank of risk factors over time. For example, subjects who rank high for unfavourable risk profiles at a young age are likely to maintain their ranks into adulthood. 5,13 Several longitudinal observational stu- dies have been conducted to examine the tracking patterns of children’s body mass index (BMI). 1,14,15 However, few studies have focused on tracking of health-related variables such as overweight and BMI from early childhood to adolescence, and studies on tracking within high birth weight populations are scarce. Revealing the degree of tracking and identifying important predictors is critical in designing effective intervention strategies. Received 29 June 2005; revised 18 November 2005; accepted 14 December 2005; published online 21 February 2006 Correspondence: Dr E Johannsson, Center for Sport and Health Sciences, Iceland University of Education, 840 Laugarvatn, Iceland. E-mail: erljo@khi.is International Journal of Obesity (2006) 30, 1265–1271 & 2006 Nature Publishing Group All rights reserved 0307-0565/06 $30.00 www.nature.com/ijo