26 October 2026 (Navroze Bureau) People who prefer staying awake late at night and struggle to wake up in the morning may share certain characteristics associated with a possible subtype of depression, according to new research. Scientists have identified a profile called “circadian depression”, which is linked to disruptions in the body’s internal clock and may help explain why some people respond differently to commonly prescribed antidepressants.
The research was conducted by scientists at the University of Sydney and published in the British Journal of Psychiatry in October 2026. Researchers analysed clinical and genetic information from more than 11,000 people who had experienced severe, recurrent or persistent depression. The findings suggest that understanding sleep timing and daily biological rhythms could eventually help doctors personalise depression treatment.
However, researchers stress that being a night owl does not automatically indicate a mental health condition. The proposed subtype is an emerging research concept, and further studies are needed to establish its clinical usefulness.
What Is Circadian Depression?
Circadian rhythms are the body’s natural 24-hour cycles that help regulate sleep, wakefulness, hormone release, body temperature and other biological processes. These rhythms are influenced by environmental signals, particularly daylight, which helps the brain coordinate the sleep-wake cycle.
When a person’s internal clock does not align well with their daily routine, they may experience difficulties sleeping, morning tiredness, low energy and reduced daytime activity. Researchers believe these patterns may be particularly relevant for some people experiencing depression.
In the study, approximately 2,604 participants, representing around 23 per cent of the sample, met the researchers’ proposed criteria for circadian depression. The profile was identified using several features, including a preference for evening activity, delayed sleep timing, difficulty waking up, excessive sleepiness, seasonal changes in mood and a mismatch between biological sleep patterns and everyday schedules.
The findings suggest that depression may involve different underlying patterns in different groups of people. Recognising these differences could eventually help healthcare professionals identify more suitable treatment approaches.
Why Researchers Are Studying Night Owls
People naturally differ in their preferred sleep schedules. Some feel most alert early in the morning, while others become more productive later in the evening. These differences are often described as chronotypes.
An evening chronotype, commonly known as being a night owl, is not a disorder in itself. Problems may arise when a person’s natural sleep schedule repeatedly conflicts with work, education or family commitments.
For example, someone whose body clock favours sleeping late may have to wake up early every day. Over time, this mismatch can contribute to insufficient sleep, morning fatigue and difficulties maintaining a regular routine.
In the new research, people who met the proposed circadian depression criteria were more likely to report morning tiredness, longer sleep during depressive episodes and seasonal patterns in their symptoms. They also tended to experience depression earlier in life and reported more severe symptoms than participants who did not meet the criteria.
The researchers also observed higher reported levels of suicidal thoughts and other complex symptoms in the circadian group. These findings underline the importance of proper mental health assessment, rather than relying on sleep habits alone to judge someone’s psychological wellbeing.
Could This Depression Subtype Respond Differently to Treatment?
One of the most important aspects of the study was its examination of treatment response. Common antidepressants, including selective serotonin reuptake inhibitors (SSRIs) and serotonin-norepinephrine reuptake inhibitors (SNRIs), are widely used to treat depression.
The analysis found that participants classified as having circadian depression reported somewhat poorer responses to these medicines and more side effects than those in the comparison group.
Researchers suggested that treatments targeting circadian rhythms, including appropriately supervised light therapy and certain melatonin-related approaches, may deserve further investigation for people with this profile.
Light exposure, sleep scheduling and behavioural interventions can influence the body’s internal clock. However, the findings do not establish a universal treatment plan, and the study did not prove that every person with circadian features will respond better to these approaches.
People taking antidepressants should not stop, reduce or change their medication on the basis of these findings. Anyone experiencing persistent symptoms or medication side effects should discuss their treatment with a qualified healthcare professional.
What the Findings Mean for Mental Health
The study offers a potential new way to understand why depression can look different from one person to another. It also raises the possibility that information about sleep timing, morning alertness and seasonal mood changes could eventually help clinicians make more personalised treatment decisions.
Nevertheless, there are important limitations. The research focused on people with significant histories of depression, so the findings cannot be applied directly to everyone who stays up late. The proposed classification also needs independent replication and further testing before it can be treated as an established clinical diagnosis.
The results do not show that being a night owl causes depression. Sleep patterns and depression can influence one another, and genetics, life circumstances, physical health and other factors may also contribute.
For people concerned about their mental health, maintaining a reasonably consistent sleep schedule, getting daylight during waking hours and seeking professional advice for persistent low mood may be helpful steps. These habits are not substitutes for treatment when depression is present.
The central message from the research is that sleep timing may offer valuable information about some forms of depression, but a person’s preferred bedtime alone cannot determine their mental health. More research is needed to establish how circadian patterns can be used safely and effectively in clinical care.