Hair cortisol concentrations as a putative biomarker for suicidal behavior.

Suicide is the 2nd leading cause of death for young adults in the United States, and rates are particularly high among psychiatric patients in the year following psychiatric hospitalization. However, the prediction of suicidal behavior continues to be a challenge. We examined hair cortisol concentrations (HCC)-reflecting HPA axis activity over the preceding months-as an objective marker of risk for suicidal behavior across the full spectrum of suicidal behavior, including death by suicide. Participants were 238 young adults across the spectrum of suicide (i.e., suicide; suicide attempt; suicidal ideation; psychiatric comparison; 57% male) and 43 individuals who died by drug overdose (56% male). Data were collected via self-report, clinical interview, medical records review, and hair sampling (i.e., 3 cm segments). Multivariate regression models were used to examine the relationship between group and HCC, controlling for covariates. HCC was significantly lower in individuals who died by suicide compared to those with a suicide attempt [Difference in EMMs (SE) = -0.64 (0.20), p = 0.010, d = 0.73], suicidal ideation [Est. Diff (SE) = -0.89 (0.20), p < 0.0001, d = 1.02], and psychiatric comparison individuals [Est. Diff (SE) = -0.74 (0.26), p = 0.022, d = 0.85]. Lower HCC may serve as an objective marker that signals risk for death by suicide among high-risk adults, which have important clinical implications for the prediction and prevention of suicide. Future studies with larger sample sizes are needed to replicate these findings and to make assaying HCC accessible for its translation into clinical practice.