The relationship between early life trauma, anxiety, and the experience of chronic pain in adulthood, and the role of inflammatory biomarker C-reactive protein

Abstract

When investigating factors that may relate to chronic pain experiences in adulthood, adverse childhood experiences (ACEs) and anxiety should be considered as important contributors. However, evidence of these associations is scattered, typically based on small cross-sectional samples, and unclear. Consequently, this thesis had two aims. First, to summarise the existing literature on the relationship between ACEs, anxiety, and chronic pain experiences in adults. Second, to examine these associations, as well as the potential impact of inflammatory biomarker C-reactive Protein (CRP), within large, representative cohorts. It was hypothesised there would be a significant positive association between childhood adversity/trauma, anxiety, and chronic pain experiences. Chapter Two is a systematic literature review (SLR) and meta-analysis; while Chapters Three and Four used structural equational modelling (SEM), general linear modelling (GLM), and Poisson regressions on existing data from two separate UK- and US-based cohorts. The narrative summary in Chapter Two revealed a significant association between ACEs, anxiety, and chronic pain experiences in adults. The meta-analyses showed moderate associations between anxiety and chronic pain, between ACEs and anxiety, and indicated that participants who experienced ACEs are around twice as likely to present with chronic pain during adulthood. Chapter Three focused on the analyses of the UK Biobank database, which found that ACEs interacted with CRP to predict chronic pain experiences. The results in Chapter Four, analysing the Midlife in the United States (MIDUS) data, helped support and validate the results of the UK Biobank analysis. It revealed CRP was significantly correlated with anxiety, emotional abuse, physical neglect, socio-demographic variables, and chronic pain presence, but childhood adversity, anxiety, and CRP did not independently predict chronic pain. However, there were several interactions between these variables that did predict chronic pain experiences, such as ACEs with CRP and with gender. The MIDUS data also allowed investigations into the influence of childhood adversity on long-term medication use for chronic pain, which were found to be complex, with significant interactions between childhood abuse types, and between CRP and socio-demographic variables. Chapter Five presents an overall Discussion of the findings of this thesis, such that these three studies supported the hypothesis that ACEs and anxiety influence chronic pain experience in adults, with the cohort data from Chapters Three and Four advancing the literature by suggesting potential mechanisms of the impact of ACEs on chronic pain via inflammation, as well as the substantial role socio-demographic variables play. The findings contribute to both academic/clinical guidance and perspectives for future research, policy changes, and improving healthcare screening practices. The implications are also discussed, such that ACEs should be considered in public health policies and decision-making, particularly in intervention/preventative programmes. Implementing screening measures and/or identification of those with co-occurring anxiety, inflammation, and chronic pain would be important for future public health strategies and could be incorporated into treatment algorithm processes.