title: Genetic effects on physical activity: results from the Swedish Twin Registry.
abstract: OBJECTIVE
  The aim of this study was to investigate the genetic effects on leisure-time physical activity using data from the Swedish Twin Registry.
  
  
  METHODS
  We investigated 13,362 twin pairs (5334 monozygotic and 8028 dizygotic pairs) aged 14-46 yr. Information on leisure-time physical activity was obtained by questionnaire. Correlations and odds ratios of physical activity were calculated for males, females, and monozygotic and dizygotic twins, respectively. Structural equation modeling was used to estimate the contribution of genetic effects as well as common and nonshared environmental factors on leisure-time physical activity.
  
  
  RESULTS
  About one third of the twins reported that they exercised regularly (26% in females and 39% in males). The correlations of physical activity were twice as high in monozygotic compared with dizygotic twins, suggesting the presence of genetic effects. The variation in physical activity due to heritage was 57% (95% confidence interval (CI) = 0.49-0.63) in males and 50% (95% CI = 0.49-0.55) in females. The common environmental influence on physical activity was very small compared with the influence from environmental factors unique to the individual.
  
  
  CONCLUSIONS
  Our study establishes heredity as an important component behind individual differences in physical activity in adult men and women. This may be one reason behind difficulties in convincing people to adopt an active lifestyle. Still, this study shows that there is a substantial influence on physical activity from environmental factors unique to the individual.
authors.affiliation: Division of Epidemiology, Stockholm Centre of Public Health, and Department of Epidemiology, Institute of Environmental Medicine, Karolinska Institutet, Stockholm, Sweden. sofia.carlsson@imm.ki.se
authors.forename: Sofia
authors.initials: S
authors.lastname: Carlsson
authors.forename: Tomas
authors.initials: T
authors.lastname: Andersson
authors.forename: Paul
authors.initials: P
authors.lastname: Lichtenstein
authors.forename: Karl
authors.initials: K
authors.lastname: Michaëlsson
authors.forename: Anders
authors.initials: A
authors.lastname: Ahlbom
mesh_terms: D000293:Adolescent; D000328:Adult; D005260:Female; D006801:Humans; D007899:Leisure Activities; D008297:Male; D008875:Middle Aged; D009043:Motor Activity; D012042:Registries; D011795:Surveys and Questionnaires; D013548:Sweden; D014427:Twins / Q000235:genetics*