Smoking cessation in people living with cardiovascular disease and mental illness: exploring the evidence base for clinician intervention

Introduction: Smoking is a leading behavioural cause of death worldwide, with particularly detrimental effects on individuals with cardiovascular disease (CVD) and mental illness. Despite the known harms of smoking, there is a gap in understanding the impact of smoking cessation on patient outcomes and the role of clinicians in offering smoking cessation support. This thesis investigates the impact of smoking cessation on individuals with CVD and mental illness, and the role of clinicians in offering smoking cessation support to these populations. Objectives: The objectives of this research were threefold: 1) to quantify the reduction in harm to CVD and mental health outcomes resulting from smoking cessation; 2) to assess the prevalence and effects of recorded smoking cessation treatments at the primary care level for patients diagnosed with CVD, with and without co-existing mental health disorders; 3) to evaluate the impact of messages framed around responsibility on the likelihood of GPs offering smoking cessation support to their patients. Methods: The research was structured into four projects. In Chapter 2, a Cochrane systematic review and meta-analysis of observational data was conducted to investigate the impact of smoking cessation on individuals living with coronary heart disease. Chapter 3 featured three confirmatory co-primary analyses (multivariable regression models, propensity score-matching models and instrumental variable regressions) to evaluate the association between smoking cessation and mental health outcomes using data from a large randomised controlled trial. Chapter 4 involved a retrospective cohort study using anonymised UK primary care patient records from the QResearch primary care research registry and assessed the prevalence and effects of recorded smoking cessation interventions for patients diagnosed with CVD, with and without co-existing mental health disorders. Finally, Chapter 5 implemented a between-subjects experimental online study to evaluate the impact of messages framed around responsibility on the likelihood of GPs offering smoking cessation support to their patients. Results: My systematic review of 68 studies demonstrated that smoking cessation significantly reduces the risk of secondary CVD events (Chapter 2), and my secondary analysis (Chapter 3) showed that quitting smoking was associated with improved mental health in people with and without mental illness, however instrumental variable analysis was underpowered. Despite these demonstrated benefits of smoking cessation, analysis of a GP database (Chapter 4) showed low cessation rates among people with CVD and mental illness and low recorded rates of smoking cessation support. My framing study (Chapter 5) demonstrated that responsibility frames, especially professional obligation, could potentially impact doctors' intention to offer smoking cessation support. However, a discrepancy was noted between self-reported attitudes of medical doctors and medical students towards smoking and health guidelines. Conclusion and Future Research: This thesis underscores the urgent need for smoking cessation interventions and support for people with CVD and mental illness, contributing to the growing body of research addressing health intersectionality. It also highlights the need for future policy to prioritise shifting clinicians’ opinions of smoking, aligning their attitudes with the objectives of health policy to ensure the effective implementation of smoking cessation support. Future research should focus on strategies to increase evidence-based cessation support and explore the discrepancy in attitudes towards smoking among medical professionals.