Author	J.L. Brown
Author	A. Steptoe
Author	J. Wardle
Abstract	People with higher levels of positive wellbeing may enjoy better health and live longer, but it is not clear why. This thesis explores the notion that links between positive wellbeing and health-relevant biological correlates could provide some explanation for the relationship between positive wellbeing and health. Two complementary approaches were used. First, associations between the positive personality trait of resilience (the ability to withstand chronic stress or adversity) and various biological and psychological factors were explored using secondary data. Second, an intervention study was used to test causal mechanisms between changes in positive wellbeing and changes in biology. Resilience (from the Resilience Scale), psychosocial stressors and affect and wellbeing outcomes were assessed in around 200 healthy working women as part of the Daytracker study. Measures of cortisol and heart rate variability (HRV) were also collected across a work and leisure day. Results of regression analyses suggested that higher resilience was associated with greater HRV across the work period, but there was no association with cortisol. Resilience mediated the relationship between particular stressors and affect and wellbeing outcomes. A two week gratitude-based intervention in 119 healthy women was used to try to increase positive wellbeing. Psychological and biological factors (cortisol, blood pressure and heart rate) were assessed before and after the intervention. The gratitude condition was associated with increased optimism, reduced depressive symptoms and lower diastolic blood pressure. However, associations with measures of positive wellbeing were not robust. It was therefore not possible to demonstrate causal links between changes in positive wellbeing and changes in biology. Future studies could focus on strengthening positive wellbeing intervention tasks. Overall the results provided modest evidence for links between positive wellbeing and biological correlates of health. Resilience may provide cardiac health protective effects, since reduced HRV has previously been associated with increased cardiovascular disease incidence.