Disruptions to the body’s internal clock may be responsible for up to a quarter of all depression cases, according to a major new study published in the British Journal of Psychiatry. The findings suggest that a distinct subtype of depression, termed “circadian depression,” is closely linked to irregularities in the sleep–wake cycle and daily activity patterns.
The research, led by a team at the University of Sydney, analysed population and genetic data to identify individuals whose depression symptoms were strongly associated with body clock disruptions. These individuals experienced disrupted sleep, low energy, and reduced physical activity during the day, and their symptoms tended to be more severe and begin at a younger age compared to other forms of depression.
According to the study, people with circadian depression were more likely to exhibit at least three out of six signs of body clock dysregulation. These included being an “evening type,” going to sleep later than most people, feeling extremely tired upon waking regardless of sleep duration, sleeping more during depressive episodes, sleeping in late on non-work days, and experiencing pronounced seasonal changes in mood, energy, sleep, and appetite.
Co-author Emiliana Tonini, a circadian researcher at the University of Sydney, said the findings indicate that disruptions to the circadian rhythm or sleep–wake cycle—such as those caused by daylight saving time changes or major life events like having a child—could trigger or worsen depression symptoms in this group. “It’s not only about the quantity or the amount of sleep, it’s really about the rhythm and the regularity of sleep,” Tonini told reporters.
Experts say the results could have significant implications for the treatment of depression. Current standard antidepressants appear to be less effective for those with circadian depression, according to the study. Instead, therapies that target the body clock, such as melatonin supplements or behavioural strategies like early morning sun exposure, may offer new avenues for relief.
Depression has long been associated with chemical imbalances in the brain, but researchers increasingly recognise that it is a complex condition with multiple subtypes and causes. The identification of circadian depression highlights the need for more personalised approaches to diagnosis and treatment, particularly for patients who do not respond to conventional therapies.
Despite the promising findings, researchers caution that the results are preliminary. Further studies are needed to confirm the existence of circadian depression as a distinct disorder and to determine the most effective interventions. Clinical guidelines have not yet been updated to reflect these insights, and experts urge caution before making changes to current treatment protocols.
The study’s authors and other specialists in the field agree that more evidence is required before circadian depression can be formally recognised or included in diagnostic manuals. In the meantime, the research is expected to prompt further investigation into the role of body clock disruptions in mental health and may encourage clinicians to consider circadian factors when assessing and treating depression.
The image accompanying this article is an AI-generated illustrative depiction inspired by the actual scene of the event.
