Background: Historically, cut-points for childhood and adolescent overweight and obesity have been based on population-specific percentiles derived from cross-sectional data. To obtain cut-points that might better predict overweight and obesity in adulthood, we examined the association between childhood body mass index (BMI) and adult BMI status in a longitudinal cohort. Methods: Using data from the International Childhood Cardiovascular Cohort (i3C) Consortium pooled cohort we determined childhood overweight and obesity cut-points that best predict BMI status at the age of 18. Logistic regression analysis was used to assess the association between BMI in childhood and adult obesity. Area under the Receiver Operating Characteristic curve was used to assess the ability of fitted models to discriminate different BMI status groups in adulthood. The cut-points were then compared to those defined by the International Obesity Task Force (IOTF) using cross-sectional data, and tested for sensitivity and specificity in a separate, independent longitudinal sample with BMI measurements available from both childhood and adulthood. Findings: The cut-points derived from the longitudinal i3C Consortium data were lower than the IOTF cut-points. Consequently, a larger percentage of the sample was classified as overweight or obese when using the i3C cut-points in the independent sample. The i3C cut-points were better than the previously used IOTF cut-points at discriminating those who would later become overweight or obese in early adulthood from those whose BMI was normal when tested in the independent sample. Interpretation: The childhood BMI cut-points based on the i3C Consortium longitudinal data provide better predictors of future risk of adult overweight and obesity than estimates based on cross-sectional data. The result is more specific identification of the childhood population at risk of adult overweight or obesity than the currently used IOTF standards. Funding: Authors Kartiosuo, Ramakrishnan, Lemeshow, Juonala, Daniels, Sabin, Hu, Prineas and Dwyer declare no support from funding organisations for their work. Authors Woo, Jacobs, Steinberger, Urbina, Bazzano and Sinaiko declare their work was supported by the National Institutes of Health (NHLBI) grant no. i3C R01 HL121230. Dr Burns declares the acquisition and management of historic Muscatine Study data was supported by a Specialized Center of Research (SCOR) in Atherosclerosis, Lipids and Thrombosis grant from the National Heart, Lung and Blood Institute (NHLBI) HL-14230; M01-FR59 and RR-00059 from the General Clinical Research Centers Program, NCRR, NIH; and the Lipid Research Clinics Program (NIH-NHLBI-N01-HV-2-2913-L). Dr Raitakari declares The Young Finns Study has been financially supported by the Academy of Finland: grants 286284, 134309 (Eye), 126925, 121584, 124282, 129378 (Salve), 117787 (Gendi), and 41071 (Skidi); the Social Insurance Institution of Finland; Competitive State Research Financing of the Expert Responsibility area of Kuopio, Tampere and Turku University Hospitals (grant X51001); Juho Vainio Foundation; Paavo Nurmi Foundation; Finnish Foundation for Cardiovascular Research ; Finnish Cultural Foundation; The Sigrid Juselius Foundation; Tampere Tuberculosis Foundation; Emil Aaltonen Foundation; Yrjo Jahnsson Foundation; Signe and Ane Gyllenberg Foundation; Diabetes Research Foundation of Finnish Diabetes Association; EU Horizon 2020 (grant 755320 for TAXINOMISIS); European Research Council (grant 742927 for MULTIEPIGEN project); and Tampere University Hospital Supporting Foundation. Dr Venn declares the CDAH follow-up study received grant support from the National Health and Medical Research Council (APP211316). Dr. Bazzano is also supported in part by the following grants from the National Institutes of Health: R01AG041200, R21057983, R01062309, K12HD043451, and P20GM109036. Declaration of Interest: All authors have declared no conflict of interest. Ethical Approval: The following studies used in the work were covered by ethical approval detailed as follows: The protocols for all relevant Muscatine Study data acquisition were approved by the University of Iowa Institutional Review Board. Informed consent was obtained from all parents and adult participants; assent was obtained from participants while they were children/adolescents. The Princeton and NGHS studies were approved by the IRB at Cincinnati Children’s Hospital Medical Center. The NGHS cohort all study participants or their legal guardian if <18 years, provided written informed consent according to local IRB requirements. The Young Finns Study was approved by the institutional ethics committees, and written informed consent was obtained from all the study participants. The CDAH study was approved by the Tasmanian Health and Medical Human Research Ethics Committee. Participants gave informed consent. The Bogalusa Heart Study was approved by the institutional review board at Tulane University.
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