Do psychosocial predictors affect the following days' cortisol awakening response? Expanding the temporal frame with which to explore morning cortisol.

Much of the extant cortisol awakening response (CAR) literature posits that CAR is an anticipatory response to perceived demands later that same day. However, expanding and switching the temporal order of cortisol and psychosocial influences may motivate more flexible approaches to understanding the dynamic relationship between mind and body, including cumulative strain on the HPA axis. This study was novel because we used two models to explore the effects of one day's emotion regulation and cortisol levels on cortisol and CAR the following day in 100 mildly stressed adults aged 50-81 years old, which contrasts with the more common CAR-anticipatory-response design. In the first model, High negative-affect-variation on day 1 predicted a higher risk of having a flat CAR the next day, relative to the moderate-affect-variation group (RR = 10.10, p < .05). In the second model, higher bedtime cortisol on day 1 was positively associated with waking cortisol (β = .293, p < .01) and flatter CAR slopes on day 2 (β = -.422, p < .001). These results show that morning cortisol intercepts and slopes may be associated with previous days' affect variability and levels of bedtime cortisol. These results also suggest that anticipation of demands may extend to the previous day, rather than just the morning of the demand, indicating a broader temporal framework for the study of CAR.