Genetic and environmental influences on insomnia symptoms and associated cognition and arousal in young adults

Abstract

Current, influential theories of insomnia emphasise the role of cognitive and arousal factors in the development and maintenance of insomnia. Even though we know that insomnia is heritable, genetic influences have not been given enough attention in these models of insomnia. This thesis investigates the extent to which genes and the environment influence these cognitive and arousal variables (and their subscales) and their associations with insomnia symptoms. Furthermore, the theory that insomnia can be subtyped into insomnia with short sleep duration and insomnia with normal sleep duration (being distinguishable by for example differences in arousal) has not yet been tested. Data came from 862 individuals (aged 22 to 32, mean age 25, 34% males) of Wave 5 of the G1219 twin/sibling sample. The five studies reported in the current thesis investigated: 1) Mindfulness 2) Pre-sleep arousal 3) Dysfunctional beliefs about sleep (DBAS) and their associations with insomnia symptoms; 4) Non-shared environmental factors associated with DBAS; and 5) Self-reports of insomnia with short versus normal sleep duration. Mindfulness, pre-sleep arousal and DBAS (and their subscales) were all found to be associated with insomnia symptoms. Mindfulness was found to be familial, while DBAS had no familial influence. Pre-sleep arousal showed moderate, significant genetic influence. No genetic or shared environmental influence was found for the associations between mindfulness and symptoms of insomnia, depression and anxiety, nor was any found for the association between DBAS and insomnia symptoms. Genetic influences were important in the relationship between pre-sleep arousal and insomnia symptoms. Furthermore, for DBAS, drug use was a non-shared environmental influence un-confounded by genetic factors. The theory of subtypes of insomnia (short versus normal sleep duration) could not be confirmed. The findings provide novel insight into the concept and aetiology of insomnia, by integrating the behavioural genetics perspective into the current theories of insomnia.