Purpose: Many individuals fail to get the recommended amount of sleep per night, despite the fact that sleep duration is associated with physical and psychological health. While many characteristics of sleep are heritable, there are discrepancies in heritability estimates for sleep duration as age, sample size, and measures of sleep duration vary (h2=0.00-0.52; Barclay et al., 2010, Sletten et al., 2013). Sleep pressure and duration change throughout development, with adolescence showing particular growth. The purpose of this study is to assess the heritability of weekday and weekend sleep duration for in a longitudinal sample of adolescents as they mature into young adults.
Methods: Participants included 857 same-sex twins from the Longitudinal Twin Sample at the University of Colorado Boulder (54%MZ; 51% female). They were primarily Caucasian (86.6%), and born between 1986 and 1990. Sleep duration was assessed at 4 time-points spanning adolescence through early adulthood for both weekday and weekend sleep (W1: Mean Age 13.12 (SD=1.82), W2: M = 17.26 (SD = 0.64), W3: M = 21.07 (SD= 2.02), W4: 22.28 (SD = 1.28)). Participants were asked, “About how many hours of sleep do you usually get each week night?” followed by “How about on weekend nights?” Answer options included: <=5, 6, 7, 8, 9, 10, 11+, or, would rather not answer.
Analyses: The present study investigated: (1) the heritability of weekday and weekend sleep duration at each time-point using univariate (AE) twin models; (2) whether was there significant stability throughout development or if unique genetic influences come online; and (3) to what degree did weekday and weekend sleep share genetic effects using a series of Cholesky decompositions.
Results: Mean sleep durations decreased over time, with shorter average weekday sleep durations compared to weekend sleep. Heritability estimates for weekday sleep ranged from h2=0.15 (age 21) to h2=0.43 (age 23), and weekend sleep ranged from h2=0.13 (age 12) to h2=0.38 (age 17). Overall heritability increased as individuals aged. We examined genetic stability across time and found evidence for shared genetic variation between earlier sleep and later sleep: at ages 12 to 17 (rA=0.61, SE=0.13) and 21 to 23 (rA=0.99, SE=0.01) for weekday sleep and from 17 to 21 (rA=0.46, SE=0.17) and 21 to 23 (rA=0.61, SE=0.16) for weekend sleep. Lastly, we asked whether the same or different genetic variation contributed to weekday and weekend sleep within time-points, and we found shared genetic variation at all time-points ranging from rA=0.44 to 0.92.
Conclusion: Weekday and weekend sleep duration are moderately heritable from adolescence to young adulthood, and at least some of the same additive genetic variation contributes to heritability both across time and across weekday and weekend sleep.
References:
Barclay, NLN, Eley, TCT, Buysse, DDJ, Rijsdijk, FV, & Gregory, AM. (2010). Genetic and environmental influences on different components of the Pittsburgh Sleep Quality Index and their overlap. Sleep, 33(5), 659–68.
Sletten, TL, Rajaratnam, SMW, Wright, MJ, Zhu, G, Naismith, S, Martin, NG, & Hickie, I. (2013). Genetic and environmental contributions to sleep-wake behavior in 12-year-old twins. Sleep, 36(11), 1715–22.
