Is hypertension the link between depression and cardiovascular disease?

Both cardiovascular disease (CVD) and depression contribute a great deal to the disease burden around the world, and particularly in Kosovo. There is strong evidence that depression and CVD are causally linked. Several hypotheses support the notion of hypertension as a causal mediator of the association between depression and CVD. However, the mechanisms underlying the prospective relationship between depression and CVD remains poorly understood. Identifying mechanisms of this relationship is of great public health relevance towards improved CVD prevention and would greatly contribute towards cardiovascular epidemiology.
The overarching purpose of this dissertation was to elucidate the prospective association between depressive symptoms and blood pressure-related outcomes. Specifically, the dissertation aims to assess the potential effects of depression and depressive symptoms on change in blood pressure, hypertension diagnosis and hypertension control. Further, the dissertation will provide novel and updated evidence of the burden of depression, CVD and their risk factors in Kosovo.
Part of the dissertation work involved implementing a cohort study in Kosovo. Primary healthcare users aged 40 years and above were recruited consecutively between March and October 2019 from 12 Main Family Medicine Centers across Kosovo. Cohort data were collected annually in two phases, approximately 6 months apart, with an expected total follow-up time of 5 years. The dissertation also uses longitudinal data from the Swiss Cohort Study on Air Pollution and Lung and Heart Diseases in Adults from waves 2, 3 and 4. Multivariable censored regression was used to assess the prospective association between depression or depressive symptoms and change in systolic and diastolic blood pressure. Multivariable logistic regression was used to assess the prospective association between depression or depressive symptoms with hypertension diagnosis.
The dissertation provides evidence on the burden of hypertension, CVD risk factors and depression in Kosovo. Poor nutrition (85%), physical inactivity (70%), obesity (53%), and smoking (21%) were common risk factors among PHC users, contributing to the CVD burden in the country. Although mental health in Kosovo appears to have improved since reports from the early 2000s, moderate to very severe depressive symptoms were still highly prevalent (12.1%) in 2019. These findings highlight the importance of CVD-centered epidemiological studies in the Kosovo context for stakeholders and policy-makers.
We found that, within the same sample, depression was associated with both smaller age-related increases in blood pressure and an increase in odds of hypertension diagnosis. The dissertation, therefore, contributes to cardiovascular epidemiology by further elucidating the prospective association between depression and CVD through different pathways involving blood pressure. These findings can be explained first by shared biology between depression and lower blood pressure, while higher healthcare utilization among people with depression may explain the observed increase in odds of having underlying hypertension diagnosed.
Taken together, hypertension is not a likely causal mediator in the association between depression and CVD. The findings of this dissertation help explain the mixed evidence on the prospective association between depression and hypertension. The dissertation also provides evidence that depression and hypertension are still important disease burdens in Kosovo which need improved prevention. This thesis points to the important need for further research into other possible pathways between depression and CVD given their high contribution to disease burden and disability.