Sleep Duration and Area-Level Deprivation in Twins.
OBJECTIVE
We used quantitative genetic models to assess whether area-level deprivation as indicated by the Singh Index predicts shorter sleep duration and modifies its underlying genetic and environmental contributions.


METHODS
Participants were 4,218 adult twin pairs (2,377 monozygotic and 1,841 dizygotic) from the University of Washington Twin Registry. Participants self-reported habitual sleep duration. The Singh Index was determined by linking geocoding addresses to 17 indicators at the census-tract level using data from Census of Washington State and Census Tract Cartographic Boundary Files from 2000 and 2010. Data were analyzed using univariate and bivariate genetic decomposition and quantitative genetic interaction models that assessed A (additive genetics), C (common environment), and E (unique environment) main effects of the Singh Index on sleep duration and allowed the magnitude of residual ACE variance components in sleep duration to vary with the Index.


RESULTS
The sample had a mean age of 38.2 y (standard deviation [SD] = 18), and was predominantly female (62%) and Caucasian (91%). Mean sleep duration was 7.38 h (SD = 1.20) and the mean Singh Index score was 0.00 (SD = 0.89). The heritability of sleep duration was 39% and the Singh Index was 12%. The uncontrolled phenotypic regression of sleep duration on the Singh Index showed a significant negative relationship between area-level deprivation and sleep length (b = -0.080, P < 0.001). Every 1 SD in Singh Index was associated with a ∼4.5 min change in sleep duration. For the quasi-causal bivariate model, there was a significant main effect of E (b(0E) = -0.063; standard error [SE] = 0.30; P < 0.05). Residual variance components unique to sleep duration were significant for both A (b(0Au) = 0.734; SE = 0.020; P < 0.001) and E (b(0Eu) = 0.934; SE = 0.013; P < 0.001).


CONCLUSIONS
Area-level deprivation has a quasi-causal association with sleep duration, with greater deprivation being related to shorter sleep. As area-level deprivation increases, unique genetic and nonshared environmental residual variance in sleep duration increases.
Department of Neurology, University of Washington (UW), Seattle, WA.|University of Washington Sleep Center, UW, Seattle, WA.|University of Washington Twin Registry, UW, Seattle, WA.
Nathaniel F
NF
Watson
Department of Psychology, University of Virginia, Charlottesville, VA.
Erin
E
Horn
University of Washington Twin Registry, UW, Seattle, WA.|Departments of Epidemiology and Medicine, UW, Seattle, WA.
Glen E
GE
Duncan
University of Washington Twin Registry, UW, Seattle, WA.|Departments of Epidemiology and Medicine, UW, Seattle, WA.
Dedra
D
Buchwald
Department of Psychiatry and Behavioral Sciences, UW, Seattle, WA.
Michael V
MV
Vitiello
Department of Psychology, University of Virginia, Charlottesville, VA.
Eric
E
Turkheimer
D000328:Adult; D019352:Censuses; D004777:Environment; D005260:Female; D059647:Gene-Environment Interaction; D006801:Humans; D008297:Male; D008957:Models, Genetic; D012042:Registries; D057566:Self Report; D012890:Sleep / Q000235:genetics* / Q000502:physiology*; D012959:Socioeconomic Factors; D013997:Time Factors; D014429:Twins, Dizygotic / Q000235:genetics* / Q000706:statistics & numerical data*; D014430:Twins, Monozygotic / Q000235:genetics* / Q000706:statistics & numerical data*; D014861:Washington; D044465:White People / Q000235:genetics
area-level deprivation; dizygotic; monozygotic; sleep duration; twins