University of Sydney researchers identify circadian depression subtype

Researchers at the University of Sydney have identified a potential new subtype of clinical depression termed ‘circadian depression’. A study published in the British Journal of Psychiatry, which analyzed clinical and genetic data from over 11,000 Australians, suggests that approximately 23% of individuals with severe or recurrent depression meet the criteria for this subtype.

Unlike seasonal affective disorder, circadian depression is not limited to specific times of the year. It is characterized by a disruption in the body’s internal 24-hour clock, often manifesting as ‘social jet lag’. Key diagnostic criteria include waking up feeling extremely fatigued, identifying as a night owl, sleeping significantly later on free days compared to work days, and experiencing seasonal shifts in mood, weight, or energy levels.

The study found that individuals with this subtype often experience an earlier onset of depression and more severe symptoms, including suicidal ideation and brief hallucinations. Notably, these patients appeared less likely to respond effectively to standard serotonin-based antidepressants. Researchers suggest that treatments targeting the biological clock, such as light therapy and melatonin, may offer more effective personalized care for this specific group.