The overarching aim of this thesis was to advance current understanding of genetic and environmental influences on multiple aspects of mental health, including wellbeing and symptoms of anxiety and depression (i.e., ‘illbeing’). In particular, this thesis aimed to shed light on the role of social factors, which are conceptualised as key determinants of wellbeing and risk of mental disorders in several psychological theories, for mental health in adulthood. We applied multiple statistical methods and research designs to study the role of genetic, environmental, and social factors as potential sources of wellbeing and symptoms of common mental disorders (i.e., anxiety and depression) in adults.
More specifically, we examined the empirical structure of the wellbeing construct and its underlying genetic and environmental underpinnings, networks of environmental factors and multiple aspects of mental health in the general population, associations between social factors and wellbeing when accounting for unmeasured familial confounding, and direct and indirect genetic effects (i.e., genetic effects of close family members mediated through the environment) on maternal depressive symptoms across the early childbearing years.
There are several conclusions which are drawn from the results of the studies comprising this thesis. First, the wellbeing construct empirically consists of multiple first-order wellbeing factors, which load on a higher-order wellbeing factor, and which show moderate genetic and substantial environmental influence. Social aspects may also be fundamental to the wellbeing construct itself. Second, key associations between environmental factors and mental health in the general population are between perceiving the social environment positively and better mental health and between having recently experienced discrimination and poorer mental health. Furthermore, many environmental characteristics show complex interrelationships and are jointly related to mental health. Third, diverse social factors remain robustly associated with wellbeing in adulthood when accounting for unmeasured familial confounding. These social factors also show moderate genetic and substantial non-shared environmental influence. Fourth, indirect genetic effects from close family members, which operate through the environment, influence maternal depressive symptoms at several timepoints after birth. This highlights how genes and environments are intricately linked and the importance of intrafamilial influences on maternal depressive symptoms. Together, the findings accentuate the importance of social factors for multiple aspects of mental health in adulthood.