Australian Researchers Identify 'Circadian Depression' Subtype Linked to Body Clock Disruption

Researchers defined circadian depression as at least three of six features: a seasonal pattern of illness, delayed sleep timing, sleeping longer when depressed, being a night owl, waking feeling very tired, and social jetlag, described as sleep on workdays differing sharply from weekends or free days. The study’s first author, Dr Emiliana Tonini of the University of Sydney’s Brain and Mind Centre, said at a press briefing that people with the subtype had more severe mental health symptoms, younger onset of depression, more episodes, more complex trajectories, more suicidality and more hypomanic and psychotic-like symptoms than those with non-circadian depression.

The researchers also found higher genetic risk for ADHD and mood disorders among people with circadian depression, along with a series of metabolic and inflammatory markers, Tonini said. She said this indicated the subtype was “not just depression with bad sleep” but had an underlying biology distinct from other forms of depression. The researchers suggested people with the subtype may benefit from treatments targeting circadian rhythms, such as melatonin and light therapy.

Prof Ian Hickie, a psychiatrist and co-director of the Brain and Mind Centre, said the critical issue was poor response to standard therapies typically recommended in guidelines. The study found SSRIs and SNRIs, common first-line antidepressant drugs, were less effective and had more side effects for people with the circadian subtype. Hickie said chronobiological treatments focused on the sleep-wake cycle, especially morning light exposure, daylight activity, regularity of sleep-wake cycles and regular food schedules, were critical.

The researchers noted that participants were limited to those of genetically inferred European ancestry, which may limit generalisability, and that future studies are needed to replicate the findings in diverse samples.

Prof Jayashri Kulkarni, director of the Monash Alfred Psychiatry Research Centre, who was not involved in the research, described it as a “really well-conducted study.” She said the polygenic risk score tied certain types of depression to a specific genetic profile, which would be important for onward treatment. Kulkarni added that the research did not take into account the hormonal impacts of menopause, which is predominantly one of the things women describe as causing sleep disturbance and would be another factor worth considering. Prof Andrew Coogan, a behavioural neuroscientist at Maynooth University in Ireland, said researchers have known for a long time that major depression is linked to body-clock changes that make people later to bed and later to rise, so the findings are not overly surprising. He cited a lack of detail as to how the cluster of features and criteria for the proposed subtype was arrived at and said the results of the exploratory study are best interpreted as initial if interesting findings that warrant further examination.