Individual differences in latent trait cortisol (LTC): Implications for the onset and course of future depressive symptoms.

Research suggests that various indicators of hypothalamic pituitary adrenal (HPA) axis activity prospectively predict depression, but few studies have evaluated whether trait indicators of HPA axis activity are related to depression. Further, no prior study has examined links between trait cortisol and psychopathology using a trait indicator that captures HPA axis activity over multiple time points. Here we examined whether we could construct an across-wave latent trait cortisol (LTC) factor using cortisol samples collected over 13 weeks, and whether the across-wave LTC prospectively predicted new depressive symptom onsets and symptom duration. Emerging adults (n = 85; M age = 19.37 years) provided salivary cortisol samples four times a day (waking, 30 min and 45 min post-waking and bedtime) over three 3-day measurement waves separated by 6 weeks. Diagnostic interviews at 3 timepoints (baseline, 1- and 2.5 years post-baseline) assessed lifetime and current depressive symptoms. Results indicated that the across-wave LTC predicted new onsets of depressive symptoms and longer symptom duration. Follow-up tests revealed that the link between the across-wave LTC and new onsets was not significant after adjusting for past depressive symptoms. These findings suggest that an indicator of individual differences in HPA axis regulation has implications for depressive symptom onsets and course.