title: Trends in parent-child correlations of childhood body mass index during the development of the obesity epidemic.
abstract: BACKGROUND
  The intergenerational resemblance in body mass index may have increased during the development of the obesity epidemic due to changes in environment and/or expression of genetic predisposition.
  
  
  OBJECTIVE
  This study investigates trends in intergenerational correlations of childhood body mass index (BMI; kg/m2) during the emergence of the obesity epidemic.
  
  
  METHODS
  The study population was derived from the Copenhagen School Health Records Register, which includes height and weight measurements since birth year 1930. Mothers and fathers with BMIs available at ages 7 (n = 25,923 and n = 20,972) or 13 years (n = 26,750 and n = 21,397), respectively, were linked through the civil registration system introduced in 1968 to their children with BMIs available at age 7 years. Age- and sex-specific BMI z-scores were calculated. Correlations were estimated across eight intervals of child birth years (1952-1989) separately by sex. Trends in these correlations were examined. Whereas the mother-child correlations reflected the biological relationship, a likely decline in the assignment of non-biological fathers through the registration system across time must be considered when interpreting the father-child correlations.
  
  
  RESULTS
  The BMI correlations between mothers and sons ranged from 0.29-0.36 and they decreased marginally, albeit significantly across time at ages 7-7 years (-0.002/year, p = 0.006), whereas those at 13-7 years remained stable (<0.0004/year, p = 0.96). Mother-daughter correlations ranged from 0.30-0.34, and they were stable at ages 7-7 years (0.0001/year, p = 0.84) and at 13-7 years (0.0004/year, p = 0.56). In contrast, father-son correlations increased significantly during this period, both at ages 7-7 (0.002/year, p = 0.007) and at ages 13-7 years (0.003/year, p<0.001), whereas the increase in father-daughter correlations were insignificant both at ages 7-7 (0.001/year, p = 0.37) and at ages 13-7 years (0.001/year, p = 0.18).
  
  
  CONCLUSIONS
  During the obesity epidemics development, the intergenerational resemblance with mothers remained stable, whereas the father-child BMI resemblance increased, possibly reflecting changes in family relationships, and unlikely to have influenced the epidemic.
authors.affiliation: Institute of Preventive Medicine, Frederiksberg and Bispebjerg Hospital, Frederiksberg, Denmark.
authors.forename: Teresa A
authors.initials: TA
authors.lastname: Ajslev
authors.affiliation: Institute of Preventive Medicine, Frederiksberg and Bispebjerg Hospital, Frederiksberg, Denmark.
authors.forename: Lars
authors.initials: L
authors.lastname: Ängquist
authors.affiliation: Population Research Unit, Department of Social Research, University of Helsinki, Helsinki, Finland.
authors.forename: Karri
authors.initials: K
authors.lastname: Silventoinen
authors.affiliation: Institute of Preventive Medicine, Frederiksberg and Bispebjerg Hospital, Frederiksberg, Denmark; Novo Nordisk Foundation Center for Basic Metabolic Research, Faculty of Health and Medical Sciences University of Copenhagen, Copenhagen, Denmark.
authors.forename: Jennifer L
authors.initials: JL
authors.lastname: Baker
authors.affiliation: Institute of Preventive Medicine, Frederiksberg and Bispebjerg Hospital, Frederiksberg, Denmark; Novo Nordisk Foundation Center for Basic Metabolic Research, Faculty of Health and Medical Sciences University of Copenhagen, Copenhagen, Denmark.
authors.forename: Thorkild I A
authors.initials: TI
authors.lastname: Sørensen
mesh_terms: D000293:Adolescent; D000328:Adult; D015992:Body Mass Index; D002648:Child; D058872:Epidemics; D005260:Female; D006801:Humans; D008297:Male; D009765:Obesity / Q000453:epidemiology*; D010290:Parents; D012737:Sex Factors