Toward a transdisciplinary science of health and wellbeing spanning psychological science and epidemiology: a focus on vagal function

Abstract

Health and wellbeing are now much studied and contested topics in science. The work presented in this thesis focuses on heart rate variability (HRV), a measure extracted from the electrocardiogram and index of vagal function with links to psychological flexibility, social engagement, and future health and wellbeing. At the heart of this body of work is a desire to better understand the relationship between mental, physical and social health. A total of thirteen published papers are included in this thesis, bridging the gap between psychological science and epidemiology. In papers one and two, I examine the associations between common mental disorders (and antidepressants) and coronary heart disease (CHD), highlighting the association between mental and physical ill-health. Papers three and four investigate whether depression or its treatment are associated with vagal impairment, a major source of debate and discussion in the field. Paper five is a randomised controlled trial of oxytocin, the mammalian neuropeptide, to determine whether oxytocin might augment resting state HRV, a fundamental psychophysiological feature of social behaviour. In paper six, I examine whether alterations are observed in women with a prior history – but not current – anxiety disorders and their offspring to determine potential adverse impacts on future generations. In paper seven, the major outcome of the work I conducted at the University of São Paulo, I examine the association between common mental disorders, antidepressant treatments and vagal function in the largest cohort to date. Paper eight and nine are follow-up studies to this that further explore whether specific subtypes of depression display more robust reductions in HRV, and whether there are differential associations of the selective serotonin reuptake inhibitors on HRV. In paper ten, I examine whether carotid intima-media thickness (cIMT) – a measure of subclinical atherosclerosis – is greater in people with anxiety and depressive symptoms. Paper eleven extends on this idea to examine whether insulin resistance and cIMT mediate the relationship between HRV and executive function. In the final two papers, I present two major syntheses of the extensive literature base on vagal function – including my own research outcomes – and provide two overarching and complimentary theoretical models linking psychological science and epidemiology, with an eye toward further scientific insights and public health outcomes. In conclusion, vagal impairment may provide a ‘spark’ that triggers a downstream cascade of adverse physiological effects that could lead to increasing morbidity and premature mortality. This body of work represents the first steps towards a transdisciplinary science of health and wellbeing, spanning psychological science and epidemiology, providing a platform for future research activity.