This pre-registered study examines the longitudinal relationships between well-being, hair cortisol (a biomarker linked to poor health), and self-reported health. Accumulated cortisol output over three months was determined quarterly over the course of one year using hair samples. Well-being was assessed as affective well-being (via experience sampling), cognitive well-being (i.e., life satisfaction), and eudaimonic well-being (via the Ryff Scales of Psychological Well-Being). Self-reported health was measured using one item on the current state of health. The longitudinal analyses allowed for disentangling initial between-person differences from within-person changes and were based on a large panel study of working-age people (N = 726). The results indicate that hair cortisol levels were generally not associated with any of the examined well-being facets, regardless of the level of analysis. Further, deviations from well-being trait levels were not linked to subsequent within-person changes in hair cortisol (and vice versa), challenging the notion that cortisol output is a key physiological pathway through which well-being improves health. In contrast, self-reported health was positively correlated with affective, cognitive, and eudaimonic well-being at both the trait and within-person levels, whereas deviations from well-being trait levels were generally not associated with subsequent within-person changes in self-reported health, and vice versa.
