Overview
- The peer-reviewed paper published in October 2026 used data from 11,380 people in the Australian Genetics of Depression Study and classified about 2,604 (roughly 25%) as having a proposed circadian subtype based on meeting at least three of six sleep–circadian features.
- People in the circadian group tended to develop depression younger, reported more severe symptoms and suicidal thoughts, were more often female, and said common antidepressants helped them less and caused more side effects.
- Genetic analyses found the circadian group had higher polygenic risk scores for ADHD, major depression, anxiety, bipolar disorder and several metabolic or inflammatory traits, suggesting a partly distinct biological profile.
- Authors and outside experts stressed key limits: the subtype was defined from retrospective self-report, the sample was genetically inferred European ancestry, and the study lacked objective circadian measures such as melatonin timing or actigraphy.
- Next steps include replication in more diverse cohorts and randomized clinical trials testing circadian-targeted therapies — including an announced melatonin trial — before changing clinical guidelines or routine practice.