Researchers at the University of Sydney’s Brain and Mind Centre have identified a distinct subtype of depression characterized by disruptions to the body’s internal clock, termed “circadian depression.” The findings, published in the British Journal of Psychiatry, were based on analysis of clinical and genetic data from 11,380 Australians predominantly experiencing severe and recurrent depression, with the new subtype identified in approximately 23% of the study population.
The research defines circadian depression through the presence of at least three of six specific features: seasonal mood patterns, delayed sleep timing, extended sleep duration during depressive episodes, nocturnal chronotype, severe morning fatigue, and social jetlag—a mismatch between weekday and weekend sleep schedules. Study lead Dr. Emiliana Tonini noted that individuals with this subtype demonstrated more severe mental health symptoms overall, with earlier depression onset, greater episode frequency, and elevated rates of suicidality and psychotic-like features compared to those without circadian dysfunction.
Genetic analysis revealed that people with circadian depression carried higher genetic risk factors for attention deficit hyperactivity disorder and mood disorders, alongside distinct metabolic and inflammatory markers. According to Prof. Ian Hickie, a psychiatrist and co-director of the research center, this circadian subtype exhibits poor responsiveness to conventional therapies. Standard antidepressants including SSRIs and SNRIs demonstrated reduced effectiveness and increased side effects in this population.
The researchers propose that chronobiological interventions targeting the sleep-wake cycle—such as morning light exposure, daytime activity engagement, and sleep-wake regularity—may provide more effective treatment options. Study authors acknowledged limitations, including the restriction of participants to individuals of genetically inferred European ancestry, noting that future research should examine diverse populations to establish broader applicability of the findings.
While external experts praised the study’s methodological rigor and polygenic risk scoring approach, some raised questions regarding the development of the diagnostic criteria and suggested the findings warrant further validation before widespread clinical application.
Article Attribution | Read More at Article Source
Article summary produced by Claude AI