Depression and sleep: what has the treatment research revealed and could the HPA axis be a potential mechanism?

Research indicates that insomnia improvement plays a critical role in depression symptom improvement. In line with the National Institute of Mental Health Experimental Therapeutics approach recent research focuses on identifying specific mechanisms; the present manuscript aims to review recent research on one potential mechanism, dysfunction in the HPA axis which is a shared biological substrate of both depression and insomnia. Over the past five years, research demonstrated a relationship between sleep disturbance and cortisol reactivity and recovery following a stressor. Meanwhile, research on the relationship between depression and HPA axis functioning is less consistent and is dependent on measurement of HPA axis. Experimental research that aims to determine a causal pathway between sleep, depression and HPA axis functioning is needed.