According to a study published on 20 October 2026 in the British Journal of Psychiatry, 23% of 11,380 adults in an Australian cohort of people who had experienced depression showed a "circadian" profile linked to the body clock: sleeping much more during episodes, feeling exhausted on waking, and a strong preference for evenings. These people reported depression that started earlier and was more severe, and slightly less benefit from two major classes of antidepressants. It is an observational study that tested no treatment and still needs to be confirmed.
- The study: 11,380 Australian adults with a lifetime diagnosis of depression, with online questionnaires and genetic data.
- The subtype: at least 3 of 6 criteria related to sleep-wake timing and the seasons. 2,604 people met the definition.
- The findings: earlier depression (18.7 years on average versus 23.2) that was more severe, and slightly higher genetic risk scores, notably for ADHD and for an "evening" profile.
- The limits: self-reported data, no biological measure of the body clock, people of European ancestry only, provisional criteria, no replication yet.
The body clock, chronotype and sleep timing, in plain words
Your body runs on rhythms of about 24 hours, called circadian rhythms, coordinated by a master clock in the brain, the suprachiasmatic nucleus. According to the US National Institute of General Medical Sciences (NIGMS), light and dark are the signals with the strongest influence on it: based on the light your eyes receive, it controls, among other things, melatonin, a hormone that rises in the evening and makes you sleepy.
Your chronotype is your natural tendency to be a morning person or an evening person. We explain the biology in Night Owl or Morning Lark? The Biology of Your Body Clock. Two other ideas appear in the study:
- Sleep midpoint: the time halfway through your night. If you sleep from 1 am to 9 am, it is 5 am. The later it is, the more your clock is shifted towards the evening.
- "Social jetlag": the gap between your sleep midpoint on free days and on work days. A large gap points to an imposed schedule out of step with your clock.
What the researchers did
The team at the University of Sydney's Brain and Mind Centre (including first author Emiliana Tonini, Jacob Crouse and Ian Hickie) put to the test an idea that several of its members had proposed in a 2021 literature review: a "circadian depression" in which disrupted sleep-wake rhythms sit at the heart of the illness.
The data come from the Australian Genetics of Depression Study, which recruited volunteers through invitation letters from the Australian government and a media campaign. The analysis covers questionnaires collected between 2016 and 2018. People were classed as having the circadian subtype if they met at least 3 of these 6 criteria:
- a high score for seasonal changes in mood and behaviour;
- a late sleep midpoint on free days, with age-adjusted cut-offs;
- marked social jetlag;
- describing themselves as "definitely an evening type";
- hypersomnia, meaning sleeping much more than usual, during their worst depressive episode;
- feeling "very tired" in the first half-hour after waking.
What they found
A common profile in this sample. 2,604 participants (23%) met the definition. They were younger on average (37.9 years versus 45.6) and more often women (80% versus 73%). The most frequent criteria among them were hypersomnia (84%) and morning tiredness (83%), followed by evening chronotype (68%) and seasonality (41%).
Earlier and heavier depression. The first episode came at 18.7 years on average, versus 23.2 years in the rest of the sample. People with the subtype also reported more psychological distress, more physical complaints, more suicidal thoughts and more (hypo)manic-like or psychotic-like experiences, and more often weight gain during episodes.
Modest genetic differences. The researchers calculated polygenic risk scores, which add up the small effects of a great many genetic variants linked to a trait. People with the subtype had slightly higher scores for ADHD, depression, bipolar disorder, anxiety, insomnia, body mass index, triglycerides and insulin resistance. The clearest gap was in the genetics of chronotype, leaning towards evening. These are group tendencies: they say very little about any one individual, and they do not mean that these people have ADHD.
Slightly less reported benefit from two classes of antidepressants. Participants rated for themselves how well the antidepressants they had taken worked ("not at all", "moderately", "very well"). The circadian group had slightly lower odds of rating selective serotonin reuptake inhibitors (SSRIs, odds ratio 0.88) and serotonin-noradrenaline reuptake inhibitors (SNRIs, 0.89) as effective. There was no difference for mirtazapine or amitriptyline. This group also reported more side effects (drowsiness, fatigue and weight gain among them). These gaps are modest and rely on memory: they do not tell you whether a medicine will work for you.
What the study does not show
- No cause and effect: the data were collected at a single point in time, which, as the authors acknowledge, makes causal conclusions difficult.
- Everything is self-reported: sleep timing, treatment response and side effects come from questionnaires, with a risk of recall errors. No physiological measure of the clock (melatonin, actigraphy) was taken.
- A particular sample: Australian volunteers, three quarters of them women, all of European ancestry. The 23% figure may not apply to everyone with depression.
- Provisional criteria: the six criteria carry equal weight, their cut-offs have not been validated, and only hypersomnia was assessed during an episode, the other criteria describing lasting habits. The profile partly overlaps with so-called atypical depression and with bipolar disorder, while remaining distinct from them according to the authors.
- No treatment was tested: the study did not evaluate light therapy, melatonin or any other treatment. In the press release, Jacob Crouse says treatments targeting the circadian rhythm "may be much more relevant" for this profile: that is a hypothesis to test, not a finding. The authors themselves conclude that independent replication is needed.
- Funding and competing interests: the study was mainly funded by Australian public money (NHMRC), donations and the Wellcome Trust. Ian Hickie declares that he has led projects supported by several pharmaceutical companies. The press release specifies that he has conducted research on agomelatine, an antidepressant that acts notably on melatonin receptors, funded by the company Servier. He also advises a digital mental health company, InnoWell, in which he holds equity.
Why talk about it now?
The clocks went back in the UK and across the European Union on 25 October 2026, and the days are getting shorter. But the study looked at neither the clock change nor winter: seasonality was only one of the six criteria, present in 41% of people with the subtype. The takeaway is simpler: in some people, depression comes with very late sleep timing, much longer nights or a mood that follows the seasons. These signs are worth describing to your doctor.
To take stock before that conversation, our chronotype questionnaire places you on the morning-evening scale, the sleep quality questionnaire (PSQI) describes your nights, and the PHQ-9 questionnaire estimates the intensity of depressive symptoms over two weeks. These are self-assessment questionnaires: the result is not a diagnosis. If you take an antidepressant and recognise yourself in this profile, do not change anything on your own: talk to your doctor. On the link between sleep and mood, see also Treating Insomnia to Ease Depression and ADHD and Seasonal Affective Disorder.
If you are struggling or having thoughts of suicide, help is available. In the US, call or text 988. In the UK and Ireland, call Samaritans free on 116 123, 24 hours a day. Elsewhere, call your local emergency number. Depression can be treated, and talking about it is a first step.
Frequently asked questions
Is circadian depression an official diagnosis?
No. It is a profile proposed by researchers, with criteria that are still provisional, and it needs to be confirmed by other teams.
Does being a night owl raise the risk of depression?
This study cannot say: it only included people who had already experienced depression, and it describes associations. An evening chronotype is not an illness.
Do light therapy or melatonin work for this subtype?
This study cannot tell us, because it tested no treatment. If you are considering either, talk to your doctor, especially if you already take a treatment.
I take an SSRI and recognise myself in this profile: should I change treatment?
Not on your own. The differences observed are modest and say nothing about any one person. Any change to an antidepressant should be decided with a doctor: talk to yours, and describe your sleep and daily rhythms.
Can the clock change trigger depression?
This study did not look at it. If your mood drops clearly and lastingly as winter approaches, or at the same season every year, talk to your doctor.
References: Tonini E, Crouse JJ, Shin M, Carpenter JS, Mitchell BL, Byrne EM, et al., including Hickie IB (2026). Clinical and genetic correlates of a circadian subtype of depression in the Australian Genetics of Depression Study. The British Journal of Psychiatry, published online 20 October 2026, pp. 1-10. DOI: 10.1192/bjp.2026.10798. Cross-sectional study, n = 11,380 (2,604 with the circadian subtype). | University of Sydney (21 October 2026). Researchers identify new circadian subtype of depression | Carpenter JS, Crouse JJ, Scott EM, Naismith SL, Wilson C, Scott J, Merikangas KR, Hickie IB (2021). Circadian depression: a mood disorder phenotype. Neuroscience & Biobehavioral Reviews, 126, 79-101. DOI: 10.1016/j.neubiorev.2021.02.045 (literature review) | NIGMS. Circadian Rhythms | GOV.UK. When do the clocks change? | 988 Suicide & Crisis Lifeline | Samaritans: contact us