A study led by researchers at the University of Sydney suggests that disruptions in the body's internal clock may help explain why some people experience persistent depression and respond differently to conventional treatments.
Depression does not affect everyone in the same way. While some people experience changes in mood, energy and sleep that respond well to standard treatments, others continue to struggle despite seeking medical help. New research from the University of Sydney offers fresh insight into these differences, identifying a potential subtype of depression associated with the body's internal clock.
The researchers have termed this condition circadian depression, highlighting the possible role of the circadian rhythm, the body's natural 24-hour system that regulates sleep, wakefulness and other biological processes. The findings suggest that understanding a person's body clock may help clinicians make more informed decisions about depression treatment.
Published in the British Journal of Psychiatry, the study examined clinical and genetic information from more than 10,000 Australians who participated in the Australian Genetics of Depression Study. The findings could contribute to a more individualised approach to managing depression, particularly for people whose symptoms persist or return despite treatment.
What Is Circadian Depression?
The body's circadian rhythm influences far more than the time a person falls asleep or wakes up. It helps coordinate daily patterns in alertness, hormone activity and other essential functions. When this internal timing system is disrupted, it can affect sleep, energy levels and overall wellbeing.
In the University of Sydney study, researchers identified 2,604 participants, accounting for nearly 25 per cent of the study population, as having characteristics associated with circadian depression.
These characteristics included seasonal patterns in depressive episodes, sleeping longer than usual during periods of depression, waking up feeling persistently exhausted and a tendency to stay awake late into the night.
Although these symptoms can occur in other forms of depression and sleep-related conditions, their combination may help researchers identify a group of people whose illness has a stronger connection to circadian rhythms.
The findings also reinforce an important point: depression is a complex condition, and a single treatment approach may not work equally well for everyone.
What the Researchers Discovered
Beyond sleep-related symptoms, the study found that participants identified with circadian depression tended to experience the onset of depression earlier in life and reported more severe symptoms.
The researchers also observed associations with greater levels of suicidal thoughts and symptoms related to mania. These findings underline the importance of careful clinical assessment, particularly when depression begins at a young age or is accompanied by significant changes in mood, sleep and energy.
Genetic analysis revealed further connections. Participants in this group showed higher genetic susceptibility to certain inflammatory and cardiovascular conditions, as well as neurodevelopmental disorders such as attention-deficit/hyperactivity disorder (ADHD).
These findings point towards possible biological connections between circadian rhythms, mental health and other aspects of physical health. However, genetic associations do not establish that circadian depression directly causes these conditions, and further research will be needed to clarify the underlying mechanisms.
Why Conventional Antidepressants May Not Work Equally Well
Selective serotonin reuptake inhibitors (SSRIs) and serotonin-norepinephrine reuptake inhibitors (SNRIs) are commonly prescribed for depression. These medications influence neurotransmitter systems involved in mood regulation and can be effective for many people.
However, the study suggests that people with circadian depression may respond less favourably to some conventional antidepressant treatments and may experience more side effects.
One possible explanation is that this subtype involves biological pathways that are not fully addressed by treatments primarily targeting serotonin or serotonin and norepinephrine.
If circadian rhythms play a significant role in a person's symptoms, treatment strategies that address sleep timing and the body's internal clock may deserve greater consideration.
The findings do not mean that antidepressants are ineffective for everyone with circadian depression. Rather, they highlight the need to assess individual symptoms, treatment history and biological factors before deciding on the most appropriate course of care.
Could Light Therapy and Melatonin Offer New Options?
The researchers suggest that treatments targeting the body's internal clock could be particularly relevant for people who display circadian patterns of depression.
Light therapy is one approach that may help regulate circadian rhythms. It involves exposure to carefully timed bright light and is already used in certain conditions involving seasonal mood changes and disrupted sleep-wake patterns. Its suitability depends on the individual's symptoms and clinical circumstances.
Melatonin, a hormone involved in regulating the sleep-wake cycle, may also have a role in selected treatment plans. Certain medications designed to act on melatonin-related pathways could offer additional options for some patients.
The timing of these interventions can be important. Light exposure at different times of day can have different effects on the body's internal clock, while melatonin use requires consideration of dose, timing, other medications and individual health factors.
These treatments should therefore be discussed with a qualified healthcare professional rather than started independently. The study's findings support further consideration of circadian-focused care, but they do not establish a single treatment that will work for everyone with this subtype.
Why Early Recognition Matters
Recognising circadian patterns may be particularly valuable when depression begins during adolescence or early adulthood. According to the study's senior researchers, failing to identify these patterns could contribute to unsuccessful early treatment attempts and unnecessary side effects for some young people.
A more detailed assessment of sleep habits, daily energy levels, seasonal changes and the timing of depressive symptoms could help clinicians build a clearer picture of an individual's condition.
For people who have not experienced sufficient improvement with antidepressants, the findings also offer a reason to revisit their treatment plan with their clinician. Changes in medication or the introduction of other therapies should always be guided by professional advice.
Importantly, symptoms such as persistent exhaustion, sleeping longer than usual or staying awake late are not enough on their own to establish a diagnosis of circadian depression. A comprehensive mental health assessment remains essential.
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A Step Towards More Personalised Mental Health Care
The identification of circadian depression adds to growing scientific interest in the biological differences that may shape how people experience and respond to depression.
By combining clinical observations with genetic data, the University of Sydney researchers have highlighted a potential subgroup for which the body's internal clock may be especially relevant. The findings could help guide future research into more targeted treatments and earlier recognition of distinct depression patterns.
Further studies will be needed to validate this subtype, establish reliable diagnostic criteria and determine which circadian-focused interventions provide the greatest benefit.
For now, the research offers a valuable message: understanding depression requires looking beyond mood alone. Sleep patterns, daily rhythms, genetics and an individual's treatment history may all provide important clues.
A more personalised approach could eventually help clinicians move closer to treatments that better match each person's needs, offering renewed possibilities for those who continue to struggle with depression.