Associations between diurnal preference, sleep quality and externalizing behaviours: a behavioural genetic analysis

<jats:sec id="S0033291710001741_sec_a001"><jats:title>Background</jats:title><jats:p>Certain aspects of sleep co-occur with externalizing behaviours in youth, yet little is known about these associations in adults. The present study: (1) examines the associations between diurnal preference (morningness <jats:italic>versus</jats:italic> eveningness), sleep quality and externalizing behaviours; (2) explores the extent to which genetic and environmental influences are shared between or are unique to these phenotypes; (3) examines the extent to which genetic and environmental influences account for these associations.</jats:p></jats:sec><jats:sec id="S0033291710001741_sec_a002"><jats:title>Method</jats:title><jats:p>Questionnaires assessing diurnal preference, sleep quality and externalizing behaviours were completed by 1556 young adult twins and siblings.</jats:p></jats:sec><jats:sec id="S0033291710001741_sec_a003" sec-type="results"><jats:title>Results</jats:title><jats:p>A preference for eveningness and poor sleep quality were associated with greater externalizing symptoms [<jats:italic>r</jats:italic>=0.28 (95% CI 0.23–0.33) and 0.34 (95% CI 0.28–0.39), respectively]. A total of 18% of the genetic influences on externalizing behaviours were shared with diurnal preference and sleep quality and an additional 14% were shared with sleep quality alone. Non-shared environmental influences common to the phenotypes were small (2%). The association between diurnal preference and externalizing behaviours was mostly explained by genetic influences [additive genetic influence (A)=80% (95% CI 0.56–1.01)], as was the association between sleep quality and externalizing behaviours [A=81% (95% CI 0.62–0.99)]. Non-shared environmental (E) influences accounted for the remaining variance for both associations [E=20% (95% CI −0.01 to 0.44) and 19% (95% CI 0.01–0.38), respectively].</jats:p></jats:sec><jats:sec id="S0033291710001741_sec_a004" sec-type="conclusion"><jats:title>Conclusions</jats:title><jats:p>A preference for eveningness and poor sleep quality are moderately associated with externalizing behaviours in young adults. There is a moderate amount of shared genetic influences between the phenotypes and genetic influences account for a large proportion of the association between sleep and externalizing behaviours. Further research could focus on identifying specific genetic polymorphisms common to both sleep and externalizing behaviours.</jats:p></jats:sec>