Study objectives: To examine whether sleep duration modifies genetic and environmental influences on body mass index (BMI).
Design: Genotype-environment interaction twin study.
Setting: University of Washington Twin Registry.
Patients or participants: A population-based sample of US twins (1,088 pairs, 604 monozygotic, 484 dizygotic; 66% female; mean age = 36.6 yr, standard deviation (SD) = 15.9 yr).
Measurements and results: Participants self-reported information on height, weight, and sleep. Mean BMI was calculated as 25.3 kg/m² (SD = 5.4) and mean habitual sleep duration was 7.2 hr/night (SD = 1.2). Data were analyzed using biometric genetic interaction models. Overall the heritability of sleep duration was 34%. Longer sleep duration was associated with decreased BMI (P < 0.05). The heritability of BMI when sleep duration was < 7 hr (h² = 70%) was more than twice as large as the heritability of BMI when sleep duration was ≥ 9 hr (h² = 32%); this interaction was significant (P < 0.05).
Conclusions: Shorter sleep duration is associated with increased BMI and increased genetic influences on BMI, suggesting that shorter sleep duration increases expression of genetic risks for high body weight. At the same time, longer sleep duration may suppress genetic influences on body weight. Future research aiming to identify specific genotypes for BMI may benefit by considering the moderating role of sleep duration.
Keywords: Sleep duration; body mass index; dizygotic; monozygotic; twins.