Dysregulation of the hypothalamic-pituitary-adrenal (HPA-)axis is hypothesized to play a role in the pathogenesis of bipolar disorder (BD). Conflicting results have been reported when saliva or serum was used to measure cortisol levels. A recently developed method is to measure cortisol in scalp hair, with one cm of scalp hair representing one month. We studied whether there are differences in long-term hair cortisol levels between BD patients and healthy individuals and whether there are associations between hair cortisol, life events and disease characteristics.

Hair samples were collected in 100 BD patients and 195 healthy controls. Long-term cortisol levels were determined in 3 cm hair segments. Saliva samples were collected on two consecutive evenings. Documented disease characteristics were disease state, age of onset, psychiatric co-morbidity, and life events.

Hair cortisol levels were not statistically different in BD patients compared to healthy controls (p=0.233) and were not associated with the disease state at the moment of sample collection (p=0.978). Clinical characteristics, such as age of onset ≥30 years (p=0.004) and psychiatric co-morbidity (44.87 versus 31.41 pg/mg hair; p=.021), appeared to associate with higher hair cortisol levels. Panic disorder associated with decreased cortisol levels (22.13 versus 34.67 pg/mg hair; p=0.019). The occurrence of recent negative major life events, but not of positive major life events, was associated with an increase in HCC in BD patients.