title: Variance components models for physical activity with age as modifier: a comparative twin study in seven countries.
abstract: Physical activity is influenced by genetic factors whose expression may change with age. We employed an extension to the classical twin model that allows a modifier variable, age, to interact with the effects of the latent genetic and environmental factors. The model was applied to self-reported data from twins aged 19 to 50 from seven countries that collaborated in the GenomEUtwin project: Australia, Denmark, Finland, Norway, Netherlands, Sweden and United Kingdom. Results confirmed the importance of genetic influences on physical activity in all countries and showed an age-related decrease in heritability for 4 countries. In the other three countries age did not interact with heritability but those samples were smaller or had a more restricted age range. Effects of shared environment were absent, except in older Swedish participants. The study confirms the importance of taking age effects into account when exploring the genetic and environmental contribution to physical activity. It also suggests that the power of genome-wide association studies to identify the genetic variants contributing to physical activity may be larger in young adult cohorts.
authors.affiliation: Department of Biological Psychology, VU University, the Netherlands. jm.vink@psy.vu.nl
authors.forename: Jacqueline M
authors.initials: JM
authors.lastname: Vink
authors.forename: Dorret I
authors.initials: DI
authors.lastname: Boomsma
authors.forename: Sarah E
authors.initials: SE
authors.lastname: Medland
authors.forename: Marleen H M
authors.initials: MH
authors.lastname: de Moor
authors.forename: Janine H
authors.initials: JH
authors.lastname: Stubbe
authors.forename: Belinda K
authors.initials: BK
authors.lastname: Cornes
authors.forename: Nicholas G
authors.initials: NG
authors.lastname: Martin
authors.forename: Axel
authors.initials: A
authors.lastname: Skytthea
authors.forename: Kirsten O
authors.initials: KO
authors.lastname: Kyvik
authors.forename: Richard J
authors.initials: RJ
authors.lastname: Rose
authors.forename: Urho M
authors.initials: UM
authors.lastname: Kujala
authors.forename: Jaakko
authors.initials: J
authors.lastname: Kaprio
authors.forename: Jennifer R
authors.initials: JR
authors.lastname: Harris
authors.forename: Nancy L
authors.initials: NL
authors.lastname: Pedersen
authors.forename: Lynn
authors.initials: L
authors.lastname: Cherkas
authors.forename: Tim D
authors.initials: TD
authors.lastname: Spector
authors.forename: Eco J C
authors.initials: EJ
authors.lastname: de Geus
mesh_terms: D000328:Adult; D000367:Age Factors; D001315:Australia; D003431:Cross-Cultural Comparison; D003718:Denmark; D004777:Environment; D005260:Female; D005387:Finland; D006801:Humans; D008297:Male; D008875:Middle Aged; D009043:Motor Activity; D009426:Netherlands; D009664:Norway; D057566:Self Report; D013548:Sweden; D014429:Twins, Dizygotic / Q000235:genetics*; D014430:Twins, Monozygotic / Q000235:genetics*; D006113:United Kingdom; D055815:Young Adult