Activity mediates conscientiousness' relationship to diurnal cortisol slope in a national sample.

OBJECTIVE The present study explored pathways from the personality traits of neuroticism and conscientiousness through health-related behaviors to diurnal patterns of the stress hormone cortisol using data from a large national study. METHOD Using prospective data from the Midlife in the United States (MIDUS II) study and the National Study of Daily Experiences (NSDE II, a MIDUS substudy), hierarchical linear modeling (HLM) and Monte Carlo estimation for multilevel model mediation were used to test direct and indirect effects (via general activity level, moderate and vigorous physical activity, lifetime history of regular smoking, and alcohol consumption) of neuroticism and conscientiousness on cortisol at wakeup, diurnal cortisol slope, and cortisol awakening response (N = 960). RESULTS Initial HLM models showed greater levels of conscientiousness were associated with steeper (i.e., healthier) diurnal cortisol slope. Consistent with a hypothesized indirect biobehavioral pathway, when controlling for demographic factors, cortisol-related medications, daily stressors, and positive affect, HLM models showed the relationship between conscientiousness and diurnal cortisol slope was mediated by general activity levels. Lifetime history of smoking was associated with flatter diurnal cortisol slope, but did not mediate the effect of conscientiousness on diurnal cortisol slope. No effects were found for neuroticism. CONCLUSIONS The results support a psychophysiological model of resilience--one that provides a more complete rendering of the health-protective mechanisms of conscientiousness via hypothalamic-pituitary-adrenal axis functioning. Specifically, the mediated pathway suggests greater engagement in the activities of day-to-day life are an instrumental means by which conscientious individuals experience healthier patterns of stress hormone secretion.