The indirect effect through health-risk behaviors, however, only partially accounts for the association between personality and levels of IL-6. Thus, in addition to health-risk behaviors, personality may have a direct effect on an individual's physical health through physiological mechanisms. For example, Neuroticism-related constructs have consistently been associated with activation of the hypothalamic–pituitary–adrenocortical (HPA) axis (e.g., Mangold & Wand, 2006, Tyrka et al. 2008). Although the research on Conscientiousness and HPA reactivity is still in its infancy, some evidence suggests that conscientious individuals have lower physiological reactivity in response to a stressor and return more quickly to baseline (Zobel et al. 2004) and positive psychological traits in general are associated with lower HPA reactivity (Chida & Hamer, 2008). As such, personality has both independent and incremental effects on health, even after controlling for major behavioral contributors to health-related outcomes.
