Correlation of cortisol in 1-cm hair segment with salivary cortisol in human: hair cortisol as an endogenous biomarker

Background: Cortisol level in human hair would be an endogenous biomarker for the retrospective assessment of long-term central hypothalamo-pituitary-adrenal activity. However, no direct evidence supports that blood-related diffusion is a biologically endogenous source of hair cortisol in humans. The present study aims to validate the direct correlation between cortisol in 1-cm hair segments and salivary cortisol in healthy humans. Methods: We collected three saliva samples from the same participant at Time 1, Time 2 (1 week later) and Time 3 (2 weeks later), and hair 4 weeks later. Cortisol levels in I-cm hair segments and saliva were determined with high performance liquid chromatography tandem mass spectrometry Results: Salivary cortisol at Time I was significantly associated with that at Time 2 (r =0.514, p = 0.003), but not with that at Time 3 (r = 0.187, p = 0.305); and the one at Time 2 was significantly associated with that at Time 3 (r = 0.380, p = 0.032). Hair cortisol was significantly correlated with salivary cortisol at Time 2 (r = 0.389, p < 0.05) and average salivary cortisol (r = 0.383, p < 0.05) from three sampling. Conclusions: Our results confirmed that blood-related diffusion mechanism is a biologically endogenous source of hair cortisol.