The Moderating Effects of Regular Caffeine Use on Cortisol Reactivity under Explicit Negative-Evaluative Stress

Caffeine induces the release of cortisol (Lovallo et al., 1996) and is reported to protect against depression (Grosso et al., 2016), but the mechanism for this is unclear. It may be that caffeine use facilitates cortisol’s ability to mobilize resources amid challenges, but few studies examine how caffeine use impacts cortisol under stress. One study found higher caffeine use produces greater cortisol reactivity under cognitive and physical stress (Lovallo et al., 2006); however, social stress —which provokes large cortisol responses (Dickerson & Kemeny, 2004) –has not been examined. Therefore, we tested whether caffeine use moderates social stress exposure on cortisol reactivity, predicting caffeine users would have greater cortisol reactivity to stress. Emerging adults (n=148) who abstained from caffeine use immediately prior, were randomized to either a control or explicitly negative-evaluative condition of the Trier Social Stress Test. Saliva samples for cortisol assay were collected at four timepoints and participants self-reported caffeine use. Hierarchical linear growth curve analyses modeled cortisol across time, stress condition, and caffeine use. As expected, we found no significant main effects of regular caffeine use on baseline cortisol or reactivity. However, in a significant Caffeine Use x Stress x Quadratic Time effect, est=0.94, p=0.02, caffeine users in the negative-evaluative condition had greater cortisol reactivity than non-users. These results suggest caffeine use moderates the impact of negative-evaluative stress on cortisol reactivity. The effect of caffeine consumption on reduced depression risk observed in other studies might be due to caffeine’s ability to mobilize cortisol.