Study identifies a possible body-clock-linked form of depression
21 Oct 2026
Researchers from the University of Sydney have identified a possible subtype of depression associated with the body’s internal clock. They hope the findings could help guide more personalised approaches to treatment.
The study, published in the British Journal of Psychiatry, describes circadian depression as a form of depression with distinct biological features.
The researchers found that people who met the criteria for this subtype may respond differently to some commonly used antidepressants. Their findings also suggest that treatments targeting melatonin and light therapy could be helpful, although further research is needed.
The team analysed clinical and genetic information from more than 11,000 Australians who took part in the Australian Genetics of Depression Study and had been diagnosed with severe, recurrent or persistent depression.
About 23% of participants met the criteria for circadian depression. Around 80% of this group were women. However, the researchers noted that women made up 75% of the original study group, meaning the findings should be considered in the context of the participant mix.
To meet the criteria, participants needed to report at least three of six features linked to circadian rhythms:
- Seasonality: Depression symptoms that follow seasonal patterns.
- Delayed sleep midpoint: Sleeping and waking later than usual.
- Social jetlag: Differences in sleep timing between workdays and days off.
- Evening chronotype: A tendency to feel more alert later in the day.
- Hypersomnia: Sleeping more than usual during a depressive episode.
- Morning tiredness: Feeling excessively tired shortly after waking.
The most commonly reported features were hypersomnia, at 23.8%, and morning tiredness, at 23.3%.
The researchers also found that participants who met the criteria tended to experience depression earlier in life. The average age of onset was around 18, compared with 23 among participants with other forms of depression.
This group also reported more frequent and severe symptoms, including mania and higher levels of suicidal thoughts. Genetic analysis indicated links with an increased genetic risk for inflammatory and cardiovascular conditions, as well as neurodevelopmental conditions such as attention deficit hyperactivity disorder (ADHD).
Lead author Dr Emiliana Tonini, from the University of Sydney’s Brain and Mind Centre, said the genetic findings pointed to inflammatory and metabolic features that may distinguish this subtype from other forms of depression.
Co-author Dr Jacob Crouse explained that circadian rhythms affect more than sleep. They help coordinate many aspects of human behaviour and body function, which may help researchers understand why some people respond differently to treatment.
The team’s next area of interest is digital phenotyping, which uses tools such as wearable devices and smartphone apps to track changes in mood, mental health and physical patterns over time.
Researchers hope these measures could help clinicians better understand how symptoms change between appointments and across seasons, supporting more personalised care.
However, the findings are based on one large Australian group assessed at a single point in time. The researchers said further studies in other countries are needed to confirm the results before the proposed subtype can inform wider clinical practice.
Study identifies a possible body-clock-linked form of depression
Source: University of Sydney researchers, study published in the British Journal of Psychiatry.