Loneliness and cardiovascular reactivity to acute stress in younger and older adults

Introduction: Loneliness is considered an important determinant of wellbeing and has been associated with poorer cardiovascular health. Therefore, the examination of the psychophysiological mechanisms through which loneliness can influence health has become a priority. This thesis aims to examine the relationship between loneliness and cardiovascular reactivity (CVR) to acute psychological stress in younger and older adults. Method: This thesis consists of a systematic review and three empirical studies. Study 1 was a systematic review of past studies that sought to evaluate the association between loneliness and physiological reactivity to acute stress. Study 2 investigated the relationship between loneliness and CVR in younger adults. It also examined if this relationship varied by acute stressor type (e.g., mental arithmetic versus speech). This was followed by Study 3 which again examined the association between loneliness and CVR but this time in a sample of older adults. In addition, to investigating if this association varied by stressor type, this study also included a briefer measure of the same loneliness scale. Finally, Study 4 pooled the data from Study 2 and 3, to compare CVR to acute stress between the younger and older adults, while exploring if any differences in CVR were associated with loneliness. Results: For Study 1, the systematic review found that the majority of the available studies supported an association between loneliness and CVR to acute stress. However, the review also highlighted a few inconsistencies in previous findings such as the direction of this association across different cardiovascular parameters and variation in responses across different stressors. In Study 2, greater loneliness predicted a diminished total peripheral resistance (TPR) response to acute stress in younger adults but only to a public speaking task. When adjusting for potential confounding variables, greater loneliness was also associated with an increased heart rate (HR) response to the same speech task. In Study 3, higher levels of loneliness were related to diminished systolic blood pressure (SBP); however, this was dependent on the measure used to assess loneliness with the briefer measure being more predictive. Again, this association was found specifically in response to a speech task. Regardless of how loneliness was assessed, it was also associated with higher overall levels of TPR. In Study 4, there were differences in CVR observed between the two age groups. Greater loneliness predicted increased HR reactivity in younger adults but lower HR reactivity in older adults. Greater loneliness predicted diminished SBP to the speech task as well. Conclusions: Overall, the findings support an association between loneliness and atypical CVR to stress across age groups. Stressor type may have an important role in this relationship. While there are still a number of issues needing further research, CVR remains a plausible pathway through which loneliness may influence cardiovascular health.