Systematic review and meta-analysis of basal cortisol levels in Borderline Personality Disorder compared to non-psychiatric controls

Objective: Borderline personality disorder (BPD) is a prevalent, complex, and serious mental disorder involving multiple symptoms and maladaptive behaviour. The underlying psychobiological mechanisms involved are not yet fully understood, but increasing evidence indicates that changes in hypothalamic-pituitary-adrenal stress axis (HPA) activity may contribute to BPD. Whilst various studies have demonstrated elevated levels of cortisol (the end-product of the HPA axis) in BPD sufferers, others have presented opposite findings. Inconsistent findings may be attributable to comorbidities, collection and measurement methods, gender, and sample size. Considering these discrepancies, the aim of this systematic review and meta-analysis was to assess available studies in the scientific literature examining basal/ baseline cortisol levels in patients diagnosed with borderline personality disorder compared to non-psychiatric controls. Methods: A systematic literature review was conducted with descriptions of primary studies in addition to a meta-analysis of studies with a control group. Meta-analysis was performed using Comprehensive Meta-analysis software (CMA version 2). The effect size (Hedges' g) was calculated with random-effect model. Results: A systematic literature search identified 16 studies that met the eligibility criteria from a total of 1076 unique records initially examined. Twelve studies (N = 546; 278 borderline personality disorder and 268 non-psychiatric controls) fulfilled the inclusion criteria for meta-analysis. The standardised mean difference (Hedges' g) of basal cortisol level between BPD and control groups was -0.32 (pooled data from 12 studies; 95% confidence interval -0.56 to -0.06, p = 0.01), indicating significantly lower mean cortisol level for the BPD group. Conclusion: Cortisol as a biomarker of the HPA axis is an important and helpful measure in the study of stress disorders such as BPD. However, considerations of potential confounding factors must be considered.