Hair cortisol in a naturalistic sample of outpatients with depressive disorders - A secondary analysis of a randomized-controlled trial and a status update on psychoneuroendocrine markers for clinical practice.

Background: Psychoneuroendocrine research has for many years sought diagnostic, prognostic, and intervention-related biomarkers for clinical conditions. Hair cortisol concentrations (HCC) have been considered promising, but findings on their properties as such a biomarker, for instance in depressive disorders, remain mixed. Method: In a randomized controlled trial (RCT), the Affect Regulation Training (ART), a structured group intervention targeting emotion regulation skills, was compared with a common-factor-control (CFC) and a waitlist control condition (WLC) in an outpatient sample with depressive disorders (major depressive disorder or dysthymia, Results: Baseline HCC were neither consistently associated with clinical characteristics nor intervention effects. However, in a subsample rigorously controlled for confounding influences ( Discussion: To our knowledge, this is the first study to demonstrate psychoneuroendocrine changes during a psychotherapeutic intervention in depressive disorders - but only when rigorously controlling for confounding influences, and not accompanied by consistent cross-sectional and predictive results. Building on these and related findings in depressive disorders, we outline the relevance of controlling for confounding influences, as well as key future research avenues to advance psychoneuroendocrinologically informed psychotherapy.