title: Body mass index trajectories from 2 to 18 years - exploring differences between European cohorts.
abstract: In recent decades, there has been an increase in the prevalence of childhood overweight in most high-income countries. Within northern Europe, prevalence tends to be higher in the UK compared with the Scandinavian countries. We aimed to study differences in body mass index (BMI) trajectories between large cohorts of children from UK and Scandinavian populations.
  
  
  
  We compared BMI trajectories in participants from the English Avon Longitudinal Study of Parents and Children born in 1991-1993 (ALSPAC) (N = 6517), the Northern Finland Birth Cohorts born in 1966 (NFBC1966) (N = 3321) and 1986 (NFBC1986) (N = 4764), and the Danish Aarhus Birth Cohort born in 1990-1992 (ABC) (N = 1920). We used multilevel models to estimate BMI trajectories from 2 to 18 years. We explored whether cohort differences were explained by maternal BMI, height, education or smoking during pregnancy and whether differences were attributable to changes in the degree of skew in the BMI distribution.
  
  
  
  Differences in mean BMI between the cohorts were small but emerged early and persisted in most cases across childhood. Girls in ALSPAC had a higher BMI than all other cohorts throughout childhood, e.g. compared with the NFBC1986 BMI was 2.2-3.5% higher. For boys, the difference emerging over time (comparing the two NFBC's) exceeded the differences across populations (comparing NFBC1986, ABC and ALSPAC). BMI distribution demonstrated increasing right skew with age.
  
  
  
  Population-level differences between cohorts were small, tended to emerge very early, persisted across childhood, and demonstrated an increase in the right-hand tail of the BMI distribution.
authors.affiliation: Section for General Medical Practice, Department of Public Health, Aarhus University, Aarhus, Denmark.
authors.forename: L
authors.initials: L
authors.lastname: Graversen
authors.affiliation: MRC Integrative Epidemiology Unit, University of Bristol, Bristol, UK.|School of Social and Community Medicine, University of Bristol, Bristol, UK.
authors.forename: L D
authors.initials: LD
authors.lastname: Howe
authors.affiliation: MRC Integrative Epidemiology Unit, University of Bristol, Bristol, UK.|Institute of Preventive Medicine, Bispebjerg and Frederiksberg Hospitals, Copenhagen, Denmark.|Novo Nordisk Foundation Center for Basic Metabolic Research, Faculty of Health and Medical Sciences, University of Copenhagen, Copenhagen, Denmark.
authors.forename: T I A
authors.initials: TI
authors.lastname: Sørensen
authors.affiliation: Department of Obstetrics and Gynaecology, University of Cambridge, Cambridge, UK.|Department of Epidemiology and Biostatistics, Imperial College, London, UK.
authors.forename: U
authors.initials: U
authors.lastname: Sovio
authors.affiliation: Section for General Medical Practice, Department of Public Health, Aarhus University, Aarhus, Denmark.
authors.forename: L
authors.initials: L
authors.lastname: Hohwü
authors.affiliation: MRC Integrative Epidemiology Unit, University of Bristol, Bristol, UK.|School of Social and Community Medicine, University of Bristol, Bristol, UK.
authors.forename: K
authors.initials: K
authors.lastname: Tilling
authors.affiliation: Finnish Institute of Occupational Health, Helsinki, Finland.
authors.forename: J
authors.initials: J
authors.lastname: Laitinen
authors.affiliation: Institute of Health Sciences, University of Oulu, Oulu, Finland.|Unit of Primary Care, University Hospital of Oulu, Oulu, Finland.
authors.forename: A
authors.initials: A
authors.lastname: Taanila
authors.affiliation: National Institute of Health and Welfare, Oulu, Finland.|Department of Obstetrics and Gynecology, University of Oulu and Oulu University Hospital, Oulu, Finland.
authors.forename: A
authors.initials: A
authors.lastname: Pouta
authors.affiliation: Department of Epidemiology and Biostatistics, Imperial College, London, UK.|Unit of Primary Care, University Hospital of Oulu, Oulu, Finland.|Biocenter Oulu, University of Oulu, Oulu, Finland.|Center for Life Course Epidemiology, University of Oulu, Oulu, Finland.
authors.forename: M-R
authors.initials: MR
authors.lastname: Järvelin
authors.affiliation: Section for General Medical Practice, Department of Public Health, Aarhus University, Aarhus, Denmark.
authors.forename: C
authors.initials: C
authors.lastname: Obel
mesh_terms: D000293:Adolescent; D015992:Body Mass Index; D002648:Child; D002675:Child, Preschool; D005006:Ethnicity; D005260:Female; D006801:Humans; D008137:Longitudinal Studies; D008297:Male; D010290:Parents; D063766:Pediatric Obesity / Q000208:ethnology*; D011247:Pregnancy; D015995:Prevalence; D012537:Scandinavian and Nordic Countries; D006113:United Kingdom; D044465:White People
keywords: ALSPAC; BMI; child; cohort studies