Invisible Scars
Authors:   , Gonggrijp Bodine Margaretha Adriana 
Published: January 2025

This dissertation investigates the relationship between victimization and its impacts on mental health, physical health, and biological aging. Using data from the Netherlands Twin Register (NTR) and the Co-Twin Control Design (CTCD), the research disentangles the effects of victimization from genetic and shared environmental factors, offering a clearer understanding of its consequences.

The Co-Twin Control Design
Chapter 2 lays the methodological foundation, exploring the CTCD’s application in twin registries. This design leverages monozygotic (MZ) twins discordant for victimization, controlling for genetic and shared environmental confounders. By comparing MZ and dizygotic (DZ) twins, the CTCD provides robust insights into the causal effects of victimization. The chapter also includes simulation analyses and scripts in R, SPSS, and STATA, enhancing the reproducibility of findings.

Victimization and Mental Health
Chapter 3 examines the association between victimization and mental health outcomes, including depression, anxiety, and loneliness, in 19,867 individuals from Dutch twin families. Victimization, particularly violent and sexual crimes, correlates strongly with negative mental health outcomes. However, CTCD analyses indicate that familial factors, including genetic predispositions, partially explain these associations. Longitudinal analyses reveal that victims already exhibit elevated mental health issues before victimization, suggesting that pre-existing vulnerabilities increase the risk of victimization.

Social Support: Genetic Influences and Protective Effects
Chapters 4 and 5 explore social support as both a genetically influenced trait and a protective factor against victimization. Chapter 4 estimates that 37% of social support variance is genetic, while 63% arises from non-shared environmental factors. Chapter 5 shows that social support improves general health and reduces depression. While social support buffers the mental health impacts of victimization, CTCD analyses reveal that this effect is confounded by genetic and shared environmental factors.

Epigenetics and Biological Aging
The final chapters investigate the impact of negative life events and victimization on biological aging using epigenetic biomarkers. Chapter 6 shows that cumulative life stressors and financial problems, sexual victimization and job loss, are associated with accelerated aging, as measured by the GrimAge biomarker. Financial problems were also linked to an increased pace of aging. After additional correction, the association between cumulative life events and financial problems and epigenetic age acceleration persisted for the GrimAge biomarker. In the discordant twin analyses, these associations were significantly reduced, suggesting a complex interplay between genetics, environment, and lifestyle in influencing epigenetic aging.
Chapter 7 demonstrated that recent experiences of sexual victimization were associated with epigenetic age acceleration of respectively 4, 7, and 4 years according to the Hannum, PhenoAge, and GrimAge biomarkers, and an increase in the pace of aging by 60 days per year according to the DunedinPACE biomarker. Weaker effects were observed for life-time experiences of sexual victimization, i.e. 1 year according to the GrimAge biomarker and an increase pace of aging by 19 days per year as measured by the DunedinPACE biomarker. The observed associations only reduced slightly after adjusting for additional confounding factors. Although the MZ discordant twin analyses do not yield significant associations, the effect size was only slightly reduced when compared to the association in the full sample, suggesting that the association between sexual victimization and epigenetic age acceleration may be partly causal.

Key Findings
Collectively, the research presented in this dissertation demonstrates the association of crime victimization with individuals' mental health and biological aging, that were especially marked for victims of sexual crime victimization. Victims of sexual crimes exhibited higher levels of depression, anxiety, loneliness, and also showed accelerated epigenetic aging. By employing the CTCD, this work offers a clearer understanding of these complex relationships and sets the stage for future research aimed at further exploring the mechanisms underlying the impacts of crime victimization.