Two sides of the same coin: The associations between mental health and cardiometabolic health and the role of lifestyle behaviours in both

The overall aim of this doctoral thesis was to assess the associations between mental health and cardiometabolic health as well as the role of lifestyle behaviours in both. This was investigated through three specific objectives. The first objective was to investigate the association of declined mental health with cardiometabolic health. In Chapter 2, a systematic review and meta-analysis of 101 mainly observational studies showed that burnout and vital exhaustion symptoms were associated with approximately 30% higher odds of prevalent and 50% higher odds of incident metabolic syndrome, and with adverse metabolic measures such as obesity, poorer blood lipids and hypertension. Although potentially clinically relevant, results were not statistically significant, except for hypertension. In Chapter 3, a narrative review investigating the potential value of addressing mental disorders as a facet of four key aspects of precision medicine for type 2 diabetes (prevention, prognostics, treatment and monitoring) shows that several mental disorders are associated with a higher risk of type 2 diabetes and its complications. The review also suggests that treating some mental disorders may contribute to diabetes prevention and improved outcomes, with technological solutions offering opportunities for identification and targeted care. The second objective was to investigate the association of dietary behaviours with mental disorders and cardiometabolic health in people with type 2 diabetes. In Chapter 4, we investigated the cross-sectional associations of dietary protein intake with the prevalence and severity of depressive symptoms in 1137 Dutch adults with type 2 diabetes. We found that higher total protein intake, but not animal or plant-based protein intake, was associated with lower severity, but not prevalence, of depressive symptoms, although the clinical relevance may be limited due to the relatively small effect size. In Chapter 5, we investigate the prospective associations of eating behaviour types (cognitive restraint, uncontrolled eating, and emotional eating) with glycaemic and cardiometabolic outcomes over two years of follow-up in 1144 adults from the same cohort, and assessed the mediating role of diet and body weight. We found that uncontrolled eating was associated with higher fasting blood glucose, and emotional eating with higher blood pressure and poorer blood lipids. These associations were partly mediated by body weight but not by diet quality or total energy intake. The third objective was to investigate the feasibility of a worksite health promotion program (targeting lifestyle behaviours) to improve mental well-being and work-related vitality by performing a process and preliminary effect evaluation (Chapter 6). The process evaluation suggests that the 5-month app-based Recharge360 program is feasible to implement in a university hospital setting, but primarily among highly educated, health-conscious women, with feasible recruitment in terms of numbers but low relative to the total population (~19,500 employees). Also, high and increasing attrition rates indicating limited feasibility for retaining participants. The preliminary pretest-posttest evaluation showed potential improvements in mental well-being and mixed results for work-related vitality. Overall, this thesis adds to the body of evidence showing that mental health is associated with cardiometabolic health, with changes in one domain often resonating in the other, and that healthy lifestyle behaviours represent an important pathway for influencing outcomes in both domains. Therefore, it is important to continue promoting healthy lifestyle behaviours through a combined strategy of individual and population-based approaches across multiple contexts, with mental and physical health addressed in a more integrated manner. An overarching observation is that, in research, clinical practice, and policy, mental health and physical health are too often treated as separate domains, whereas they are in fact interconnected parts of overall health, or ‘two sides of the same coin’.