Associations between presleep arousal and insomnia symptoms in early adulthood: A twin and sibling study

Study Objectives
This study examines the associations between overall pre-sleep arousal, its cognitive and somatic subscales and insomnia symptoms. Furthermore, the relative contribution of genetic and environmental influences on overall pre-sleep arousal, cognitive pre-sleep arousal, somatic pre-sleep arousal and insomnia symptoms and the association between these variables is estimated.

Methods
The cross-sectional data came from G1219 (Wave 5), a twin/sibling study which comprised 862 individuals (aged 22-32 years, 34% males). Pre-sleep arousal was measured using the pre-sleep arousal scale and insomnia symptoms using the insomnia symptoms questionnaire.

Results
Both cognitive and somatic pre-sleep arousal were significant, independent factors associated with insomnia symptoms. Overall and somatic pre-sleep arousal showed a significant, substantial genetic influence (47% and 49% respectively) and non-shared environmental influence. For cognitive pre-sleep arousal and insomnia symptoms, non-shared environment appeared to be most important (74% and 61% respectively), and familiality was indicated. A strong, significant association of the genetic influences on overall pre-sleep arousal and insomnia symptoms was found (genetic correlation = .88). Strong, significant genetic correlations were found between cognitive pre-sleep arousal, somatic pre-sleep arousal and insomnia symptoms (genetic correlations .93 to 1). Non-shared environmental influences between these three variables were moderately, significantly correlated (non-shared environmental correlation .22 to .41).

Conclusion
The large overlap of genetic influences between pre-sleep arousal and insomnia symptoms provides novel insight into the associations between these variables. The results indicate that those with cognitive and/or somatic pre-sleep arousal may also have a genetic vulnerability to insomnia symptom