Sleep duration is attracting increasing attention in relation to chronic disease risk, but few large-scale studies have investigated the determinants of sleep characteristics in early life. In this study we used data from a large, population-based twin study to examine genetic and environmental influences on sleep duration and sleep difficulties in infancy.


Participants were 1931 pairs of young twins (3862 children) from the Gemini twin birth cohort. Sleep patterns were assessed at 15 months by using a modification of the Brief Infant Sleep Questionnaire completed by parents. Outcomes included nighttime and daytime sleep duration and frequency of night waking.


Twin analyses showed that nighttime sleep duration was predominantly influenced by the shared environment (66%, confidence interval [CI] 63%–70%) with a modest genetic effect (26%, CI 22%–30%). A similar pattern was observed for daytime nap duration (shared environment: 57%, CI 53%–62%; genetic effect: 37%, CI 33%–41%) and sleep disturbance (shared environment: 55%, 44%–64%) with a genetic effect of 40% (30%–51%). These estimates were similar for boys and girls.


These results indicate an important contribution of the shared family environment as well as genes to children’s sleep behavior. There is a need for research to identify specific environmental determinants that could provide targets for interventions to improve sleep quality.

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