title: Genetic and environmental influences on the tracking of body size from birth to early adulthood.
abstract: OBJECTIVE
  This study identified genetic and environmental influences on the tracking of body size from birth to 16 to 18.5 years of age.
  
  
  METHODS
  Longitudinal information was collected from a nationally representative sample of Finnish twin adolescents (birth cohorts 1975 to 1979) and their parents through questionnaires mailed when the twins were ages 16 and 18.5 years old. The sample included 702 monozygotic, 724 same-sex dizygotic, and 762 opposite-sex dizygotic sets of twins. The measures used were length, weight, ponderal index (kilograms per cubic meters), and gestational age at birth, and height, weight, and body mass index (kilograms per square meters) at 16 to 18.5 years of age. The changes in genetic and environmental influences on body size from birth to early adulthood were analyzed by quantitative genetic modeling.
  
  
  RESULTS
  The twins who had a higher weight or ponderal index at birth were taller and heavier in early adulthood, whereas those who were longer at birth were taller, but not heavier, later in life. Adult height was affected more by the birth size than body mass index. In the genetic modeling analyses, the genetic factors accounting for the variation of body size became more apparent with age, and both genetic and environmental influences on stature had a sizable carry-over effect from birth to late adolescence, whereas for relative weight, the influences were more age-specific.
  
  
  CONCLUSIONS
  The genetic and environmental architecture of body size changes from birth to adulthood. Even in monozygotic twins who share their genetic background, the initially larger twin tended to remain larger, demonstrating the long-lasting effects of fetal environment on final body size.
authors.affiliation: University of Helsinki, Department of Public Health, FIN-00014 Helsinki, Finland. kirsi.pietilainen@helsinki.fi
authors.forename: Kirsi H
authors.initials: KH
authors.lastname: Pietiläinen
authors.forename: Jaakko
authors.initials: J
authors.lastname: Kaprio
authors.forename: Maija
authors.initials: M
authors.lastname: Räsänen
authors.forename: Aila
authors.initials: A
authors.lastname: Rissanen
authors.forename: Richard J
authors.initials: RJ
authors.lastname: Rose
mesh_terms: D000293:Adolescent; D001724:Birth Weight; D001824:Body Constitution / Q000235:genetics*; D001827:Body Height; D015992:Body Mass Index; D001835:Body Weight; D004777:Environment; D005260:Female; D005387:Finland; D005865:Gestational Age; D006801:Humans; D007231:Infant, Newborn; D008137:Longitudinal Studies; D008297:Male; D015233:Models, Statistical; D012044:Regression Analysis; D011795:Surveys and Questionnaires; D014429:Twins, Dizygotic; D014430:Twins, Monozygotic