Key Findings of the Study
Prevalence: About 23% to 25% (2,604 participants) of individuals with depression met the criteria for the circadian subtype.
Classification Criteria: Participants needed to exhibit at least three of six binary circadian features:
- Social jetlag (significant shift in sleep schedule between work/free days)
- Seasonality
- Delayed sleep midpoint
- Evening chronotype ("night owl" preference)
- Sleep inertia (severe morning tiredness)
- Hypersomnia (sleeping longer during depressive episodes
Genetic and Biological Correlates
Using polygenic risk scores (PGS), researchers found that the circadian subtype shared higher genetic loading with:
- Mental and neurodevelopmental disorders: Major depressive disorder, bipolar disorder, and attention-deficit/hyperactivity disorder (ADHD).
- Sleep-wake traits: Delayed sleep midpoint, insomnia, and evening chronotype.
- Metabolic and inflammatory markers: Higher body mass index (BMI), triglycerides, insulin resistance, and interleukin-6 (IL-6).
Ref: Clinical and genetic correlates of a circadian subtype of depression in the Australian Genetics of Depression Study
Published online by Cambridge University Press: 20 October 2026
