Overview
- A University of Sydney team published a paper in the British Journal of Psychiatry on Wednesday that used data from 11,380 participants in the Australian Genetics of Depression Study to define a proposed subtype called circadian depression.
- The researchers classified people as circadian if they reported at least three of six features — seasonal mood change, late sleep timing, social jet lag, evening chronotype, hypersomnia during episodes, and morning grogginess — and about 2,604 participants met those criteria.
- Those in the circadian group tended to have earlier onset, more severe symptoms, more suicidality and physical complaints, and they reported poorer benefit and more side effects from common antidepressants such as SSRIs and SNRIs.
- Genetic analyses linked the proposed subtype to higher polygenic risk for ADHD, other mood disorders, metabolic traits and inflammation, which the authors say supports a distinct biological pathway tied to the body clock.
- The study relies on self-reported sleep and a largely European-ancestry Australian cohort, so experts call for replication with objective circadian measures (for example melatonin timing), broader samples and randomized trials of clock‑targeted treatments before changing diagnostic labels or prescribing practice.