A new Australian study published in The British Journal of Psychiatry proposes a distinct subtype of severe mood disorders called "circadian depression," characterized by symptoms such as waking up extremely tired, sleeping more during depressive episodes, and tending to be a "night owl."
Researchers from the University of Sydney's Brain and Mind Centre analyzed clinical and genetic data from 11,380 Australians dealing with severe, recurrent, or persistent depression. The findings revealed that roughly one in four individuals—about 2,604 participants—met the criteria for circadian depression by self-reporting specific patterns linked to the body's 24-hour internal clock. Lead researcher Emiliana Tonini noted that patients within this proposed subgroup experienced more severe mental health symptoms, including an earlier age of onset, higher rates of suicidality and mania, and a potentially distinct genetic profile that includes a higher risk for attention deficit hyperactivity disorder (ADHD).
Experts unconnected to the study, such as UNSW Professor of Psychiatry Philip Mitchell and Monash University sleep medicine expert Shanthakumar Wilson Rajaratnam, acknowledged the work as thought-provoking while emphasizing that more international research is required before the classification enters standard clinical practice. They noted potential overlaps with existing diagnoses like atypical depression and suggested that sleep complaints can heavily intersect with mood disturbances.
While circadian depression is not currently listed as a standalone diagnostic category in global manuals, researchers believe identifying the subtype could pave the way for more targeted interventions. Potential treatments include light therapy, melatonin-targeted approaches, and behavioral adjustments aimed at regulating the body's circadian rhythm to improve patient outcomes.
