Author: Natasha Wood
Wood, Natasha, 2023 Scars of Childhood Stress: An investigation of the relationship between childhood socioeconomic position, DNA methylation, and young adult mental health, Flinders University, College of Education, Psychology and Social Work
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There is evidence for an emerging link between childhood stressors, epigenetic changes, and mental health outcomes (e.g., Nöthling et al., 2019). Less research has explored epigenetic changes and mental health outcomes specifically in the context of childhood socioeconomic position, my thesis explores whether there is a mediating relationship between childhood socioeconomic position, DNA methylation, and young adult mental health outcomes. Overall, little research has investigated the mediating relationship between childhood socioeconomic position, DNA methylation, and young adult mental health outcomes. My thesis provides new and original contributions to this literature in four key ways: 1) I examined the existing literature on the relationship between childhood socioeconomic position and DNA methylation, 2) I constructed and examined a novel measure of childhood socioeconomic position, 3) I examined the relationship between DNA methylation and this novel measure of childhood socioeconomic position, and finally, 4) I investigated the mediating relationship between childhood socioeconomic position, DNA methylation, and young adult mental health outcomes.
First, my thesis articulates how prior research has primarily focused on the influence of childhood maltreatment and adversities on DNA methylation (e.g., Nöthling et al. (2019)). My thesis provided a systematic review of current literation on the relationship between childhood socioeconomic position and different types of DNA methylation, including epigenome-wide, candidate genes, and epigenetic age acceleration (Chapter 2). This work showed that despite being a growing area of research, there are several methodological issues and findings on the relationship between childhood socioeconomic position and DNA methylation are mixed (Chapter 2).
Second, my thesis constructed a novel measure of childhood socioeconomic position. Existing literature has used a variety of conceptualisations of childhood socioeconomic position, both regarding DNA methylation and in other research areas (Chapters 2 and 3). We know that some measures fail to account for sociological factors or focus on an area level when it may be more appropriate to look at individual socioeconomic position (Chapter 3). My thesis provides a unique perspective of childhood socioeconomic position by constructing a measure using both sociological and economic factors and examining childhood socioeconomic position over time (Chapter 3). I demonstrated that latent class growth analysis is suitable for modelling childhood socioeconomic position by constructing a four-class measure of childhood socioeconomic position. Additionally, I showed that measures constructed using latent class growth analyses can be used to examine distal outcomes, such as DNA methylation and mental health outcomes (Chapters 3-5).
Thirdly, my thesis examined the DNA methylation of childhood socioeconomic position. Existing literature has suggested that childhood socioeconomic position may have the potential to influence DNA methylation, (e.g., Borghol et al., 2012; Bush et al., 2018; Lam et al., 2012; Laubach et al., 2019; Needham et al., 2015), however due to inconsistencies in measurement of childhood socioeconomic position, findings are mixed. My thesis is the first to use a latent-class growth analysis as a childhood socioeconomic position predictor in this context, and to show that childhood socioeconomic position may have the potential to affect biological aging and the DNA methylation of genes associated with the secretion and release of corticotropin, a key hormone in the human stress response system.
Finally, my thesis investigated the mediating relationship between childhood socioeconomic position, DNA methylation, and young adult mental health outcomes. Using mediation analyses, I showed that there is some evidence for a mediating relationship between childhood socioeconomic position, DNA methylation, and young adult depression symptoms (Chapters 4 and 5). Specifically, I showed that this was the case for epigenetic age acceleration to mediate the relationship between the Decreasing class compared to the High class and depressive symptom scores. No such relationship was identified for the individual CpG sites.
Taken together, my findings suggest that DNA methylation may mediate the relationship between childhood socioeconomic position and young adult depression scores, but this relationship may be more salient when examining socioeconomic mobility. I hypothesise that the shift-and-persist model and homeostasis may explain why differences were only identified when the Decreasing and High class were compared. My thesis has methodological, clinical, and theoretical implications. Methodologically, my findings show that there may be benefit to developing epigenetic age acceleration measures which account for childhood socioeconomic position, and that weighted stepwise approaches with latent categorical predictors can be applied to models with DNA methylation. Clinically and theoretically my findings provide insight into the potential epigenetic programming of HPA axis, and suggest that socioeconomic position informed preventative interventions— potentially focusing on shift-and-persist strategies—may be of specific benefit for depression symptoms. Therefore, future work should aim to further explore the relationship between childhood socioeconomic position, DNA methylation, and young adult mental health outcomes through also examining gene expression and HPA axis activity.
Keywords: social epigenetics; childhood socioeconomic position; DNA methylation; epigenetics; mental health; behavioural epigenetics
Subject: Mental Health Sciences thesis
Thesis type: Doctor of Philosophy
Completed: 2023
School: College of Education, Psychology and Social Work
Supervisor: Sarah Cohen-Woods