Hair cortisol as a biomarker for mood in bipolar disorder: a pilot study

Background Bipolar disorder (BD) is characterized by episodes of manic, depressive and mixed mood states which have profound effects on the patient's quality of life. BD is diagnosed and followed up clinically using psychiatric assessment, with currently no biomarkers in clinical use for diagnosis or follow-up of the disorder. One potential biomarker is the stress hormone cortisol, but this has not been tested by comparing mood and cortisol within a cohort of people with BD. Here we asked whether hair cortisol might serve as a biomarker for mood in BD, with its advantage of averaging cortisol over months, bypassing concerns of circadian rhythm and acute stresses. Methods We measured cortisol in 2cm hair segments proximal to the scalp, which correspond to two months of hair growth. At the time hair was harvested, participants with BD were scored for depression and anxiety using the Hamilton Depression Rating Scale (HDRS), Beck Depression Inventory (BDI) and Hamilton Anxiety Rating Scale (HAM-A). We calculated partial Pearson correlations between mood scales and hair cortisol levels, accounting for participant’s age, gender, family status, education and medication. Results Hair cortisol correlated positively with mood scores in all three scales (r = 0.45–0.55, n = 38, p < = 0.01). Conclusions We conclude that hair cortisol may be a useful candidate biomarker for mood of BD patients over recent months.