By: Dr Tim Smithies
Earlier this week, my colleague shared an Australian Broadcasting Corporation (ABC) news article [1] with me about a new study published in The British Journal of Psychiatry by Tononi and colleagues at the University of Sydney [2]. The study described an analysis of over 11,000 Australians who had been diagnosed with depression at some stage of their life. The authors of the study identified a subtype of depression, characterised by “circadian disruption”. This subtype represented almost a quarter of people with depression, and was linked to more severe depressive symptoms, mania and psychotic-like experiences, suicidality and weight gain, as well as higher risk of comorbidity with attention-deficit hyperactivity disorder (ADHD), anxiety and bipolar disorder.
Circadian Disruption
Clearly, circadian disruption is something that is worth considering for clinicians when treating patients with depression. However, we know that circadian disruption is also linked to other mood disorders such as anxiety and bipolar disorder [3]. So, what is circadian disruption? Tononi and colleagues considered the people in their dataset to have circadian disruption if they had or did three of these six things:
- Seasonal changes – not only in sleep, but also mood, energy, social activity, weight and appetite
- Sleep timing that is far later than average for folks their age
- Large differences between sleep timing on workdays and free days (also called “social jet lag”)
- A late “chronotype”. Chronotype refers to individual preferences in activity timing across the day
- Hypersomnia, or excessive sleep when depression symptoms were bad
- Feeling excessively tired in the morning upon waking up
Elsewhere, circadian disruption is used as an umbrella term for challenges posed to a person’s circadian rhythm or “body clock” that cause some kind of negative outcome [4]. Circadian disruption can stem from factors we can’t fully control, such as genetics and physiological changes across the human lifespan, but it can also be influenced by external or environmental factors like natural light exposure, cultural factors, social factors, and, of course, workplace factors.
Circadian Disruption and the Workplace
A few honourable mentions aside (light levels in indoor environments, exercise and meal timings), the chief body clock disruptor in the workplace is work timing. This is mostly a problem for shift work, which occurs outside standard hours (i.e., before 7am or after 6pm). Shift work can disrupt circadian rhythms by altering sleep and light exposure patterns across the 24 hours of the day. Shift-work-related circadian disruption can impact worker alertness, performance and safety, but is also linked with increased risk of mental health disorders like depression and anxiety, as well as decreased self-reported quality of life [5].
How Can We Reduce Circadian Disruption in the Workplace?
Going back to the study I mentioned at the start, using measures or therapies that seek to address circadian disruption, such as increasing daytime light exposure and decreasing nighttime light exposure, won’t magically eradicate all mental health concerns for those with “circadian depression”; but they can help [6]. Similarly, addressing circadian disruption in the workplace won’t solve all problems team members might face, but it can help in several ways, including improving workers’ mental health, reducing absenteeism, and improving overall satisfaction. When aiming to minimise the risk of workers experiencing circadian disruption in a shift work environment, asking the following three questions is a great place to start:
- Could the roster be better designed? Roster design strongly influences body clock disruption, and in turn, worker performance and wellbeing. Our shift and roster design and operational analysis services help organisations build rosters that meet operational needs while reducing risks to workers’ performance, safety, and mental health.
- Are we educating our team on how to best manage the demands of shift work? Melius Consulting’s sleep health and fatigue education equips participants with information on the body clock, light exposure, and practical strategies to minimise the impact of circadian disruption. This can, in turn, improve worker performance, mental health, and overall work satisfaction.
- How well do we know our own team members? Factors like a late chronotype, an undiagnosed sleep disorder or existing health conditions can make some shift workers more vulnerable to circadian disruption and its effects on mental health. Our sleep health optimisation and assessment programs use validated technologies and assessment tools to identify these workers early, guide targeted interventions, and refer workers to specialists where needed.
To learn more about these services or any other services we offer at Melius Consulting, visit our website at https://meliusconsulting.com.au/ or contact me at tim.smithies@melius.com.au.
References
1. Roberts, L., One in four people with severe depression have dysregulated body clock, study suggests. ABC News [Internet]. 2026 Oct 21 [cited 2026 Oct 28]. Available from: https://www.abc.net.au/news/health/2026-10-21/circadian-depression-clinical-genetic-implications/107261644.
2. Tononi, E., et al., Clinical and genetic correlates of a circadian subtype of depression in the Australian Genetics of Depression Study. The British Journal of Psychiatry, 2026. p. 1-10. https://doi.org/10.1192/bjp.2026.10798.
3. McClung, C., Videnovic, A., Musiek, E., Circadian Dysregulation in Brain Aging and Neuropsychiatric Health. In: Kryger M. H., Roth T., Goldstein C. A., editors. Principles and practice of sleep medicine. 7th ed. Philadelphia: Elsevier; 2022. p. 433-40.
4. Vetter, C. Circadian disruption: What do we actually mean?. European Journal of Neuroscience, 2020; 51: p. 531-50. https://doi.org/10.1111/ejn.14255.
5. Drake, C.L., Wright, K.P.W. Jr., Cheng, P., Shift Work, Shift-Work Disorder, Jet Lag, and Jet Lag Disorder. In: Kryger M. H., Roth T., Goldstein C. A., editors. Principles and practice of sleep medicine. 7th ed. Philadelphia: Elsevier; 2022. p. 761-73.
6. Kang, S-G., Kim, Y-K., Chronotherapy in the treatment of major depression. In: Kim, Y-K., editor. Understanding Depression: Contemporary Issues and Dilemmas. 2nd ed. Singapore: Springer Nature; 2026. p. 415-29.