The Heritability of Insomnia

Twin studies of insomnia exhibit heterogeneity in estimates of heritability. This heterogeneity is likely due to sex differences, age of the sample, the reporter, and the definition of insomnia. The aim of the present study was to systematically search the literature for twin studies investigating insomnia disorder and insomnia symptoms and to meta-analyse the estimates of heritability derived from these studies to generate an overall estimate of heritability. We further examined whether heritability was moderated by sex, age, reporter and insomnia symptom. A systematic literature search of 5 online databases was completed on January 24th 2020. Two authors independently screened 5,644 abstracts, and 160 complete papers for the inclusion criteria of twin studies from the general population reporting heritability statistics on insomnia or insomnia symptoms, written in English, reporting data from independent studies. We ultimately included 12 papers in the meta-analysis. The meta-analysis focussed on twin intra-class correlations for monozygotic and dizygotic twins. Based on these intra-class correlations, the meta-analytic estimate of heritability was estimated at 40%. Moderator analyses demonstrated stronger heritability in females than males; and for parent-reported insomnia symptoms compared to self-reported insomnia symptoms. There were no other significant moderator effects, though this is likely due to the small number of studies that were comparable across levels of the moderators. Our meta-analysis provides a robust estimate of the heritability of insomnia which can inform future research aiming to uncover molecular genetic factors involved in insomnia vulnerability.