title: Genetic and environmental influences on insomnia, daytime sleepiness, and obesity in twins.
abstract: OBJECTIVE
  To better understand the relationships of insomnia, sleepiness, and obesity.
  
  
  METHODS
  Classic twin study.
  
  
  METHODS
  A community-based twin registry in Washington State.
  
  
  METHODS
  One thousand forty-two monozygotic and 828 dizygotic twin pairs participating in the University of Washington Twin Registry.
  
  
  METHODS
  N/A.
  
  
  RESULTS
  Twins were, on average, 32 years old; 61% were women, and 19.5% were obese, defined as a body mass index > or = 28. Insomnia and sleepiness were endorsed by 19.3% and 3.7% of twins, respectively. Twin correlations were higher in monozygotic than dizygotic twins for insomnia (0.47 versus 0.15), sleepiness (0.37 versus 0.14), and obesity (0.82 versus 0.46). Heritability estimates were 57% for insomnia (p < .001; 95% confidence interval 47-63), 38% for sleepiness (p < .01; 95% confidence interval 16-46), and 73% for obesity (p < .001; 95% confidence interval 49-87). Multivariate genetic model fitting revealed that common additive genetic effects comprised 12.8% of the phenotypic correlation between insomnia and sleepiness (p < .01) and 10% of the phenotypic correlation between insomnia and obesity (p < .01). The phenotypic correlation between sleepiness and obesity was not due to common additive genetic effects.
  
  
  CONCLUSIONS
  Insomnia, sleepiness, and obesity are under strong genetic influence. Common genetic effects were observed between insomnia and both sleepiness and obesity, suggesting shared genetic contributions to these phenomena.
authors.affiliation: Department of Neurlogy, University of Washington Sleep Disorders Center at Harborview, Box 359803, 325 Ninth Avenue, Seattle, WA 98104-2499, USA. nwatson@u.washington.edu
authors.forename: Nathaniel F
authors.initials: NF
authors.lastname: Watson
authors.forename: Jack
authors.initials: J
authors.lastname: Goldberg
authors.forename: Lester
authors.initials: L
authors.lastname: Arguelles
authors.forename: Dedra
authors.initials: D
authors.lastname: Buchwald
mesh_terms: D000293:Adolescent; D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D002940:Circadian Rhythm; D006970:Disorders of Excessive Somnolence / Q000453:epidemiology*; D004777:Environment; D005260:Female; D020022:Genetic Predisposition to Disease; D006801:Humans; D008297:Male; D008875:Middle Aged; D009765:Obesity / Q000453:epidemiology*; D010641:Phenotype; D012042:Registries; D007319:Sleep Initiation and Maintenance Disorders / Q000453:epidemiology* / Q000235:genetics*; D012895:Sleep, REM / Q000502:physiology; D014427:Twins / Q000235:genetics*