Insomnia symptom severity predicts blunted cortisol reactivity to a psychosocial stressor.

Insomnia is characterized by a state of hyperarousal, sometimes seen as increases in hypothalamic-pituitary-adrenal (HPA) axis activity (e.g., greater cortisol secretion). The evidence for the association between insomnia symptoms and HPA-axis functioning, however, is surprisingly mixed. Moreover, few studies have investigated whether insomnia is related to differences in cortisol responses to acute stressors. We used an in-lab, cross-sectional design to collect insomnia symptoms and salivary cortisol stress data from 295 young adults. Mixed effects models were used to examine whether differences in insomnia symptom severity were associated with cortisol reactivity to a psychosocial stressor. The study findings supported that greater insomnia symptoms were associated with a significantly more blunted cortisol stress response. Gender and hormonal contraceptive use were also associated with more blunted cortisol slopes, but the link between insomnia symptoms and cortisol stress reactivity remained significant even when controlling for gender and contraceptive use. These data add additional support to growing evidence that insomnia symptom severity is associated with alterations in HPA-axis functioning in response to acute laboratory challenges.