Beyond feeling blue: Longitudinal studies on the effects of depression on cardiovascular health, cognition and loneliness

In this dissertation, we studied how depression affects cardiovascular disease (CVD), cognition and loneliness. In chapter 1, we introduced the rationale, aims and outline of this thesis. In chapter 2, we studied whether time trends in the prevalence and incidence of CVD differ between older adults with and without depression. We found downward trends in the prevalence and incidence of CVD. These trends did not differ between depressed and non-depressed persons. In addition, we found that depressed persons had a higher cardiovascular risk than non-depressed persons and that this gap has not changed significantly over the past decades. These findings suggest that depressed persons have also benefitted from the favourable developments in the prevention and treatment of CVD. In chapter 3, we studied how depression and cardiovascular risk factors together influence the risk of six-year incident CVD. We found that the co-occurrence of depression and physical inactivity and the co-occurrence of depression and diabetes mellitus are associated with a disproportionate increase of the cardiovascular risk. Co-occurrence of depression and other cardiovascular risk factors was not associated with a disproportionate increase of the cardiovascular risk. Assuming causality, these synergistic effects imply that intervening on physical inactivity and diabetes mellitus can critically reduce cardiovascular risks in depressed persons. In chapter 4, we aimed to determine whether depression-related characteristics can improve the detection of incident CVD in depressed persons. Out of 15 clinical characteristics and personality traits, only anxiety symptom severity and depressive symptom severity were associated with an increased cardiovascular risk. Yet, adding these characteristics to the model with traditional cardiovascular risk factors barely improved the prediction of CVD. We conclude that, when information on traditional risk factors is available, the added value of depression-related characteristics in predicting cardiovascular risk is limited.In chapter 5, we studied how cardiovascular morbidity, depression and loneliness influence each other over time in older adults. We found prospective reciprocal risk increasing effects between depression and loneliness and a prospective risk increasing effect of cardiovascular morbidity on depression. Prospective effects of depression on cardiovascular morbidity and prospective reciprocal effects between cardiovascular morbidity and loneliness were not statistically significant and are therefore assumed to be indirect. We conclude that cardiovascular morbidity, depression and loneliness influence each other in complex ways and a deterioration of either of them could provoke a spiral of further deterioration of health. In chapter 6, we studied whether sex differences in cognitive functioning are explained by sex differences in cognitive risk factors. We found that women on average had better cognitive functioning than men. Smoking and physical activity partially explained sex differences in cognitive functioning. Obesity, systolic blood pressure and depressive symptoms suppressed sex differences in cognitive functioning. Therefore, reducing sex differences in explanatory cognitive risk factors may reduce sex differences in cognitive functioning, while reducing sex differences in suppressing cognitive risk factors may increase sex differences in cognitive functioning. A healthy lifestyle appears to be beneficial for cognitive functioning at old age.