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Abstract

Social disconnection—encompassing structural social isolation and subjective loneliness—is a recognized risk factor for cardiovascular morbidity and mortality, yet the biobehavioural and psychophysiological pathways linking social experience to cardiovascular regulation remain poorly delineated. This dissertation addresses how structural and subjective dimensions of social disconnection, including the temporal dynamics of loneliness, relate to blood pressure and vagally-mediated heart rate variability (vmHRV). In Study 1, recent residential movers (n = 26) and age- and sex-matched non-movers (n = 20) were followed for three months. Among movers, increases in local social network size predicted reductions in systolic blood pressure, an effect that remained after adjustment for demographic and health covariates. In Study 2, female university students (N = 265) were assessed at resting baseline, during a visuospatial attention task, and during experimentally induced state loneliness. Higher chronic loneliness predicted lower resting vmHRV and blunted vmHRV withdrawal to cognitive challenge, independent of psychosocial, behavioural, and demographic covariates; chronically lonely participants also reported greater negative affect and showed larger vmHRV increases during the state loneliness induction. In Study 3 (N = 151), chronic (past five years) and situational (past 24 hours) loneliness were examined in relation to vmHRV reactivity across diverse cognitive challenge tasks. Chronic loneliness predicted blunted vmHRV withdrawal during attention, perception, working memory, and executive function tasks, whereas situational loneliness showed weaker and less consistent associations. Exploratory analyses suggested especially blunted vmHRV withdrawal during working memory demands when both chronic and situational loneliness were elevated. Collectively, these studies identify complementary pathways linking social disconnection to cardiovascular regulation: greater structural social integration during a major life transition was associated with reductions in systolic blood pressure, and chronic loneliness was associated with lower resting vmHRV and reduced cardiac vagal flexibility during cognitive demands. By distinguishing between temporal dimensions of loneliness and combining longitudinal and experimental approaches, this work advances an integrated account of how social experiences may become biologically embedded, with implications for prevention and intervention targeting both social isolation and persistent loneliness.