Overview
- Researchers at the University of Sydney analysed data from 11,380 adults with severe, recurrent depression and in October 2026 classified about 2,604 people, roughly 23 percent, as meeting a proposed 'circadian' set of criteria.
- The team used a six-item catalogue of measurable circadian features and assigned people to the group if they met three or more criteria such as late sleep timing, strong morning fatigue, hypersomnia and seasonal symptom fluctuation.
- People in the circadian group reported earlier illness onset, more recurrent episodes and higher rates of suicidal thoughts and psychosis‑like experiences, and they showed higher average polygenic risk scores for ADHD, anxiety, bipolar disorder and severe depression.
- Study authors proposed circadian-targeted approaches—morning light therapy, melatonin or melatonergic drugs and fixed sleep‑timing routines—after participants said standard SSRIs and SNRIs worked less well, but those medication findings rely on retrospective self-report rather than controlled comparisons.
- External experts cautioned that many features overlap with established atypical or seasonal depression and stressed replication and randomized trials are the next steps before clinicians change practice.