Dysfunctional beliefs about sleep and insomnia symptoms in early adulthood: A twin and sibling study.

This study examines the associations between dysfunctional belief about sleep (DBAS), its subtypes and insomnia symptoms and estimates the relative contribution of genetic and environmental influences to these variables and the associations between them. The data came from G1219, a twin/sibling study that comprises 862 individuals (aged 22-32 years, 34% male). The Insomnia Symptoms Questionnaire was used to measure insomnia symptoms and a 10-item version of the Dysfunctional Beliefs and Attitudes about Sleep Scale was used to assess DBAS. A higher DBAS score was associated with more insomnia symptoms. Overall DBAS showed a mainly non-shared environmental influence (86%). The genetic correlation between overall DBAS and insomnia symptoms was large but not significant, the shared environmental correlation was very small, negative and not significant, whereas a moderate, significant overlap in the non-shared environmental influences was evident (non-shared environmental correlation = 0.32). For the association between the subscales of DBAS and insomnia symptoms no significant overlap for genetic (weak to strong associations) or shared environmental factors (very weak negative to strong associations) was indicated. Most of the non-shared environmental influences on the four variables were significantly moderately correlated (non-shared environmental correlation = 0.24-0.46). These findings help to deepen our understanding of cognitive theories of insomnia by dissecting one of its crucial elements and illuminating the factors involved in its association with insomnia symptoms.