title: Genetic, maternal and placental factors in the association between birth weight and physical fitness: a longitudinal twin study.
abstract: BACKGROUND
  Adult cardiorespiratory fitness and muscle strength are related to all-cause and cardiovascular mortality. Both are possibly related to birth weight, but it is unclear what the importance is of genetic, maternal and placental factors in these associations.
  
  
  METHODS
  Peak oxygen uptake and measures of strength, flexibility and balance were obtained yearly during adolescence (10-18 years) in 114 twin pairs in the Leuven Longitudinal Twin Study. Their birth weights had been collected prospectively within the East Flanders Prospective Twin Survey.
  
  
  RESULTS
  We identified linear associations between birth weight and adolescent vertical jump (b = 1.96 cm per kg birth weight, P = 0.02), arm pull (b = 1.85 kg per kg birth weight P = 0.03) and flamingo balance (b = -1.82 attempts to stand one minute per kg birth weight, P = 0.03). Maximum oxygen uptake appeared to have a U-shaped association with birth weight (the smallest and largest children had the lowest uptake, P = 0.01), but this association was no longer significant after adjustment for parental BMI. Using the individual twin's deviation from his own twin pair's average birth weight, we found positive associations between birth weight and adolescent vertical jump (b = 3.49, P = 0.0007) and arm pull (b = 3.44, P = 0.02). Δ scores were calculated within the twin pairs as first born twin minus second born twin. Δ birth weight was associated with Δ vertical jump within MZ twin pairs only (b = 2.63, P = 0.009), which indicates importance of placental factors.
  
  
  CONCLUSIONS
  We found evidence for an association between adolescent physical performance (strength, balance and possibly peak oxygen uptake) and birth weight. The associations with vertical jump and arm pull were likely based on individual, more specifically placental (in the case of vertical jump) factors. Our results should be viewed as hypothesis-generating and need confirmation, but potentially support preventive strategies to optimize birth weight, for example via placental function, to target later fitness and health.
authors.affiliation: Department of Pediatrics, Maastricht University Medical Centre, Maastricht, The Netherlands ; School for Oncology and Developmental Biology, Maastricht, The Netherlands ; Nutrition and Toxicology Research Institute Maastricht, Maastricht, The Netherlands.
authors.forename: Robbert N H
authors.initials: RN
authors.lastname: Touwslager
authors.forename: Marij
authors.initials: M
authors.lastname: Gielen
authors.forename: Frans E S
authors.initials: FE
authors.lastname: Tan
authors.forename: Antonius L M
authors.initials: AL
authors.lastname: Mulder
authors.forename: Willem J M
authors.initials: WJ
authors.lastname: Gerver
authors.forename: Luc J
authors.initials: LJ
authors.lastname: Zimmermann
authors.forename: Alfons J H M
authors.initials: AJ
authors.lastname: Houben
authors.forename: Maurice P
authors.initials: MP
authors.lastname: Zeegers
authors.forename: Catherine
authors.initials: C
authors.lastname: Derom
authors.forename: Robert
authors.initials: R
authors.lastname: Vlietinck
authors.forename: Hermine H
authors.initials: HH
authors.lastname: Maes
authors.forename: Coen D A
authors.initials: CD
authors.lastname: Stehouwer
authors.forename: Martine
authors.initials: M
authors.lastname: Thomis
mesh_terms: D000293:Adolescent; D000886:Anthropometry; D001530:Belgium; D001724:Birth Weight / Q000502:physiology*; D006801:Humans; D007231:Infant, Newborn; D008137:Longitudinal Studies; D010101:Oxygen Consumption / Q000502:physiology; D010809:Physical Fitness / Q000502:physiology*; D012044:Regression Analysis