Australian researchers have identified a new subtype of depression, termed “circadian depression,” which is linked to disruptions in the body’s internal clock. The study, published in the British Journal of Psychiatry, suggests this form of the illness is less responsive to traditional antidepressant treatments.
The research analyzed clinical and genetic data from 11,380 Australians, mostly those with severe and recurrent depression. The findings indicate that circadian depression affects nearly a quarter of participants, specifically 23 percent. Researchers believe that individuals with this subtype may benefit more from treatments targeting circadian rhythms, such as melatonin and light therapy, rather than standard medication.
Defining the Circadian Subtype
Dr Emiliana Tonini, the study’s first author from the University of Sydney’s Brain and Mind Centre, defined the subtype based on six specific features. To be classified as having circadian depression, participants needed to exhibit at least three of these traits: a seasonal pattern of illness, delayed sleep timing, sleeping longer during depressive episodes, being a night owl, waking up feeling very tired, or experiencing social jetlag.
Social jetlag occurs when a person’s sleep schedule during work or school days differs significantly from their schedule on weekends or free days. Tonini noted that individuals with this subtype tend to have more severe mental health symptoms. Their depression often begins at a younger age, involves more episodes, and follows a more complex trajectory. The study also found higher rates of suicidality and symptoms such as hypomania and psychosis-like experiences in this group.
Genetic analysis revealed that those with circadian depression had a higher risk for ADHD and mood disorders. They also showed distinct metabolic and inflammatory markers. Tonini emphasized that this indicates an underlying biology distinct from other forms of depression, rather than simply depression accompanied by poor sleep.
Treatment Implications and Genetic Links
Professor Ian Hickie, a psychiatrist and co-director of the Brain and Mind Centre, highlighted the poor response to standard therapies in this group. The study found that selective serotonin reuptake inhibitors (SSRIs) and serotonin-norepinephrine reuptake inhibitors (SNRIs), which are typical first-line antidepressants, were less effective for people with circadian depression. These medications also caused more side effects in this subgroup.
Hickie stated that chronobiological treatments are critical for this group. These approaches focus on the sleep-wake cycle, including morning light exposure, daylight activity, and regularity in sleep-wake cycles and food schedules. The researchers hope that clinically diagnosing this subtype in the future will allow for more tailored treatments, particularly for young people seeking mental health support for the first time.
Professor Jayashri Kulkarni, director of the Monash Alfred Psychiatry Research Centre, described the study as well-conducted. She noted the importance of the polygenic risk score used to tie specific depression types to genetic profiles. However, she pointed out that the research did not account for the hormonal impacts of menopause, which often causes sleep disturbances in women. She suggested this factor should be considered in future studies.
The study had limitations, including a participant pool limited to those of genetically inferred European ancestry. The researchers acknowledged this may limit the generalizability of the findings and called for replication in diverse samples. Professor Andrew Coogan of Maynooth University in Ireland noted that the link between depression and body clock changes is not entirely new. He suggested the results are initial findings that warrant further examination, citing a lack of detail on how the criteria for the subtype were established.
Source: The Guardian
