Affect and physical health: Studies on the link between affect and physiological processes

The main goal of this thesis was to study the association between affect and health at both the between-subject and the within-subject level. Especially for the latter, time series analyses are a necessity. Time series are formed by multiple observations in one individual, and can be collected in an intensive day-to-day study design. To reduce the burden of the research protocol on participants, we explored the possibilities of non-invasive sampling to measure biomarker levels. In addition, we explored the possibility to combine self-reported diary data with physiological data from existing technologies, like Fitbit or smartwatches. In the second part of the thesis, we examined the associations between both positive affect (PA) and negative affect (NA) and health indicators at both the between-subject and the within-subject level.
Overall, it was shown to be feasible to measure physiological biomarkers in samples which can be obtained non-invasively in an intensive day-to-day study. In addition, the findings in this thesis imply that PA has a positive effect on health.PA is inversely associated with somatic symptoms and detrimental biomarkers, both at the between-individual and the within-individual level. However, the associations found within individuals are heterogeneous, meaning that the associations differ between individuals. More research is necessary to better understand the effect of affect, the possible protective role of PA, and pathological effects of psychopathology in the long run.