One in four people with severe depression could have a newly explored subtype called circadian depression, characterized by disrupted internal body clocks, excessive daytime sleepiness, and severe symptoms starting at a younger age, according to a large population and genetics study published in the British Journal of Psychiatry.
A large population and genetics study published in the British Journal of Psychiatry examined 11,380 people of European ancestry suffering from severe depression, a condition that ranks as the second most common mental-health disorder globally. The findings establish that nearly one-quarter of those participants—totaling 2,604 individuals—met at least three out of six proposed criteria for what researchers call circadian depression.
Defining the Circadian Depression Subtype
Affected individuals tend to experience more severe symptoms that begin at an earlier age compared to people with other forms of depression. The condition is marked by disrupted sleep patterns, low energy levels, and reduced physical activity throughout the day. Demographically, they are also more likely to be female and less likely to find relief through conventional antidepressants.
- Excessive daytime sleepiness
- Feeling tired in the morning
- A preference for staying up late
- Seasonality, where changes in light and day length affect mood
- Delayed sleep
Shared Genetics Link Circadian Depression to Other Disorders
According to co-author Emiliana Tonini, a circadian researcher at the University of Sydney, this genetic overlap could mean that people with circadian depression are more vulnerable to having their symptoms triggered by shifts in their circadian rhythm or sleep–wake cycle changes, such as adjusting to daylight saving time or having a child. The study linked circadian depression to higher genetic risk factors for attention deficit hyperactivity disorder, alongside other mood disorders such as anxiety and major depressive disorder.
Co-author Jacob Crouse, another circadian researcher at the University of Sydney, noted that these findings suggest metabolic dysfunction can directly influence a person’s mood, energy levels, and sleep, as researchers also uncovered connections between circadian depression and an elevated risk of inflammation and disrupted metabolism.
Up to 68% of people fail to see an improvement in their symptoms after receiving standard antidepressants, according to data cited in the research explaining why standard treatments often fail. Colleen Loo, a clinical psychiatrist and researcher at the University of New South Wales in Sydney, Australia, describes the work as a really useful contribution to the science of understanding depression, noting that it moves the field one step further toward uncovering underlying biological mechanisms.
Tonini expressed hope that identifying whether a disrupted circadian rhythm contributes to a patient’s depression will eventually guide clinicians toward more effective treatments. Researchers in the field maintain that while the findings improve clinical understanding of potential causes, the evidence remains preliminary. More research is required before circadian depression can achieve formal recognition as a disorder or prompt changes to standard treatment guidelines.
