Environmental influences on neuroticism : a story about emotional (in)stability

High neuroticism is the single most important risk factor in public mental health, a personal burden, and a substantial cost to society. About half of the individual differences in neuroticism have a non-genetic origin. In this PhD thesis I investigated whether and how environmental influences associate with change in neuroticism, and how long such changes persist. To do so, I performed a series of longitudinal studies. Additionally, I reviewed studies on monozygotic twin pairs discordant for neuroticism (a design that reduces genetic confounding of life event occurrences) and longitudinal studies on within-individual changes in neuroticism in adults. Results indicate that increases in the setpoint of neuroticism tend to follow stressful life events (especially social stress and conflict) that can be characterized as unpredictable, uncontrollable, unexpected, undesirable, and non-normative from a life history perspective. Additionally, we critically examined the meaning of the previously reported strong prospective association between neuroticism and the common mental disorders (CMDs, viz. anxiety, depression, and substance use disorders). This was done in a series of longitudinal studies and a review of population studies in which neuroticism predicts CMDs. The key observation is that high neuroticism is, indeed, an important prospective
indicator of risk for the development of full-blown psychological disorders, and can, to some extent, be viewed as sub-threshold psychopathology. In conclusion, this thesis indicates that the neuroticism setpoint is embedded in the environment, sensitive to both positive and negative life events, consequential for future mental health, and more malleable than researchers originally believed.