One in Four Cases of Depression Could Be Caused by a Dysregulated Body Clock, Study Says

Outside experts warn that more research is needed before “circadian depression” can be classified as a subtype

Sara Hashemi | Daily Correspondent

October 22, 2026 2:15 p.m.

One in four people with depression could have a newly identified subtype called “circadian depression” caused by a dysregulated body clock, suggests a new study.

The work, published in the British Journal of Psychiatry on October 21, deepens our understanding of depression, and could lead to more effective intervention and treatment for people affected by this subtype.

“Depression is not a uniform illness and understanding the characteristics of different subtypes means that we can give people earlier access to treatments that will be most effective for them,” says study co-author Emiliana Tonini to Lauren Roberts at the Australian Broadcasting Corporation.

However, the study also had several limitations, and outside experts say that more research is still needed before circadian depression can be classified as a subtype.

To conduct the study, Tonini and her colleagues surveyed more than 11,000 Australians of European descent with severe depression and asked them about their sleep patterns, tiredness and other characteristics. The participants also provided saliva samples.

The researchers found that 2,604 people met at least three of the researchers’ criteria for circadian depression: morning sleepiness, delayed sleep timing, social jet lag, excessive sleeping during depressive episodes, and seasonality.

“It’s not only about the quantity or the amount of sleep, it’s really about the rhythm and the regularity of sleep,” Tonini explains to Alice Klein at New Scientist.

The team also found that those with the subtype had higher genetic risk factors for attention deficit hyperactivity disorder (ADHD) and mood disorders, as well as “a series of metabolic and inflammatory markers,” says Tonini to Donna Lu at the Guardian. That suggests that with circadian depression, “there is an underlying biology that is quite distinct from other forms of depression.”

Those with circadian depression tended to have more severe mental health symptoms that began at a younger age compared to those with non-circadian depression. They were also less likely to respond to standard antidepressants like selective serotonin reuptake inhibitors (SSRIs), which include drugs such as Prozac.

“One of the things I hate most in the depression world is the name ‘treatment-resistant depression’—as if, if you failed two SSRIs or an SNRI, somehow your depression won’t respond. When really, you’ve been on the wrong track since the start,” says study co-author Ian Hickie, a psychiatrist at the University of Sydney, to Euan Black at the Financial Review. For people with this subtype of depression, drugs that target the circadian system are more likely to be effective, he suggests.

The findings are “really useful because they advance the field in terms of understanding the whole circadian rhythm aspect of depression and how it might be related to biological measures like genetics and inflammatory markers,” says Colleen Loo, a clinical psychiatrist at the University of New South Wales who wasn’t involved in the work, to New Scientist.

However, they also have several limitations. For one, the study is based on self-reported data about symptoms, Loo tells Rachel Fieldhouse at Nature, so more work is needed to establish the connection between circadian rhythm and depression.

The study’s sample size was also limited to people with European ancestry; future work needs to look at people from other populations. Andrew Coogan, a behavioral neuroscientist at Maynooth University in Ireland who wasn’t involved in the work, tells the Guardian that the proposed subtype has a “lack of detail as to how the cluster of features of, and the criteria for, the proposed circadian subtype of depression was arrived at.”

“The results of this exploratory study are best interpreted as initial if interesting findings that warrant further examination,” he adds.