Study objectives: We sought to evaluate the contribution of genetic and non-genetic factors on habitual sleep/wake patterns in a community-dwelling agrarian population using a physical activity monitoring device, the Actical.
Design: Cross-sectional population-based study of healthy Old Order Amish enrolled in the Heredity and Phenotype Intervention (HAPI) Heart Study.
Setting: Lancaster County, PA, USA.
Participants: 723 healthy adults (54% men) with a mean age of 43.3 ± 13.8 years (range: 20-80). 96% of the subjects were connected into one 5-generation pedigree.
Interventions: N/A.
Measurements: Participants wore Actical accelerometers 24 hours/day for 7 days to determine physical activity level, as well as habitual wake time, bedtime, and sleep duration. Participants completed the Horne-Östberg Morningness-Eveningness Questionnaire (MEQ), a modified Epworth Sleepiness Scale (ESS), and a lifestyle questionnaire. A sub-study of 164 participants kept sleep diaries.
Results: Habitual wake time and bedtime determined by Actical were highly correlated with results from sleep diaries (r = 0.82 for wake time and 0.72 for bedtime, both P < 0.0001). After adjustment for age, sex, occupation, and season, higher activity level was associated with earlier wake time but not with bedtime, and correspondingly with shorter sleep duration. After adjustment for the aforementioned factors and the effects of a shared household, habitual wake time, MEQ score, and ESS score showed significant heritability (wake time h(2) = 0.20, MEQ h(2) = 0.21, and ESS h(2) = 0.17).
Conclusions: Objectively measured wake time, self-reported morningness-eveningness preference, and daytime sleepiness appear heritable and wake time may be associated with physical activity level.
Keywords: Actical; ESS; Epworth; Horne-Östberg; MEQ; Morningness-Eveningness; Old Order Amish; circadian; daytime sleepiness; heritability; physical activity; sleep phase.