Maternal separation in childhood and the role of biomarkers of stress in its association with mental health

Parent-child separation has been shown to increase the risk of depressive symptoms later in life. Dysregulation of the hypothalamic-pituitary-adrenal (HPA) axis may help to explain this association. However, few studies have examined the effects of separation on cortisol in late adulthood. This thesis aims to investigate the interplay between these social, psychological and biological factors. Data were from phases 7 (2002-04) to 11 (2012-13) of the Whitehall II study, when participants were aged 60 to 70 years, on average. The first two empirical chapters focus on establishing the association between maternal separation in childhood and cortisol, measured in saliva and hair. The third empirical chapter examines the association between long-term depressive symptoms and hair cortisol. Analyses were conducted using linear regression and multilevel mixed modelling. Participants who reported separation during childhood showed flatter diurnal cortisol slopes and higher hair cortisol concentrations (HCC), compared to their non-separated counterparts. Associations between separation and cortisol awakening response (CAR) and area under the curve (AUC) were not significant. An association between maternal separation and salivary cortisol was observed at phase 7 of Whitehall II but not phase 9 (2007-09). Diurnal cortisol slopes became flatter from phase 7 to 9 across all participants but the degree of change was lower in participants reporting separation. Current and recurrent, but not past, depressive symptoms were positively associated with HCC. An interaction effect between maternal separation in childhood and depressive symptoms was not significant. Maternal separation in childhood and adult depressive symptoms were independently associated with cortisol in saliva and hair in late adulthood. No evidence was found for mediating or moderating effects, suggesting that early-life stress and depression may have distinct effects on the HPA axis in later life.