OBJECTIVE: Hair cortisol is a promising new biomarker of retrospective systemic cortisol concentration. In this study, we compared hair cortisol concentrations in patients with newly diagnosed bipolar disorder (BD), their unaffected first-degree relatives and healthy individuals and identified potential predictors of hair cortisol concentrations in patients with BD.

METHOD: In a cross-sectional design, we compared hair cortisol concentrations in 181 patients with newly diagnosed/first episode BD, 42 of their unaffected first-degree relatives and 101 healthy age- and sex-matched individuals with no personal or first-degree family history of affective disorder. In patients with BD, we further investigated whether medication- and illness related variables, as well as measures of stressful life events in the preceding 12 months and childhood trauma, were associated with hair cortisol concentrations.

RESULTS: Hair cortisol concentrations were 35.1% (95%CI: 13.0-61.5) higher in patients with BD (P = 0.001) compared with healthy individuals in models adjusted for age and sex. Hair cortisol concentrations in unaffected first-degree relatives did not differ from healthy individuals (P = 0.8). In patients, neither medication, illness duration nor stress related variables were associated with hair cortisol concentrations.

CONCLUSION: We found elevated hair cortisol concentrations in patients newly diagnosed with BD indicating the presence of physiological stress in early stages of BD.