A Sydney-based study of 69 young people seeking mental health care found almost a quarter showed disrupted body clocks that showed signs that looked like jet lag, despite not having travelled across time zones. The University of Sydney researchers suggest the finding could lead to new ways to treat and study mental health conditions such as depression and bipolar disorder.
The study, led by Dr Joanne Carpenter and Professor Ian Hickie from the University of Sydney , is the first to look simultaneously at three key measures of body clock regulation in people with mental ill-health.
"We analysed participants' core body temperature, cortisol levels and melatonin levels, which we know play important roles in how our bodies manage the circadian rhythm - our 24-hour cycles which regulate things like wakefulness and sleep," said Dr Carpenter, a Research Fellow at the Faculty of Medicine and Health Central Clinical School and member of the Brain and Mind Centre's Youth Mental Health and Technology Group .
Melatonin is a hormone that signals to our bodies that it's time to sleep, while cortisol is a hormone that is found at its highest levels in the morning shortly after waking up. Our body temperature also goes through a daily cycle of rising and falling that is closely aligned with sleep.
"When we looked at these three measures in young people who presented to mental health services, we found that 23 percent of patients were experiencing a kind of physiological jet lag."
The Australian Bureau of Statistics 2023 National Study of Mental Health and Wellbeing found that almost two in five people (38.8 percent) aged 16-24 experienced a mental disorder that persisted over 12 months.
Dr Jacob Crouse , co-author of the study and academic lead of the Clinical Stream of the Youth Mental Health and Technology Team , said these results could indicate new ways to approach mental health.
"Our findings suggest we might need to think differently about what kinds of treatments we're giving people with mood disorders, and whether we should be targeting body clocks as another option for managing these conditions."
Comparing sleep cycles
The study comprised two groups - the first, young people between the ages of 16-35 who presented to mental health clinics in Sydney for treatment; the second, young people who had no prior history of mental illness.
The participants in the two groups were monitored overnight in a chronobiology lab to measure their sleep and body clock related hormones in the lead up to sleep and in the hours after they woke up. Their body temperatures were recorded continuously using a sensor that was swallowed by participants.
A chronobiology lab allows scientists to carry out research into sleep and circadian rhythms. The lab is a controlled space where factors that influence our circadian rhythms like light, activity and posture can be tightly managed to rule out external influences.
"We were able to measure melatonin and cortisol levels using saliva samples in the lead up to sleep and after participants woke, which is the first time these key markers of the circadian rhythm have been combined with body temperature to study how circadian rhythms might be misaligned in people with mood disorders," says Dr Carpenter.
"We found that 23 percent of patients had at least two of these circadian rhythm measures out of sync with each other. This is similar to the disruption we see when travelling across time zones or undertaking shift work, when the body clock becomes out of sync with the external environment. However, what we are seeing here is circadian rhythms being out of sync with each other within a person's body, a kind of 'internal jet lag'.
"While we do see teenagers sleeping later because of normal developmental shifts in the body clock to later timing across adolescence, what we are seeing here is a more extreme kind of circadian disruption where the clocks are not just delayed but not lining up with each other."
"We also found a correlation between how out of sync patient's body clocks were and the severity of their depressive symptoms," said Dr Crouse. "In particular, higher depressive symptoms were linked to core body temperature cycles that were running on an earlier clock than other rhythms and sleep-wake patterns."
The researchers note that the study doesn't establish internal jet lag as a cause of mental ill health, and that further research is needed to fully understand the link between body clock and mental health, as patient data was collected over a single sleep cycle. It will be important to follow young people with mood disorders over time to see whether body clocks and mental health change together. A small number of people in the control group also exhibited signs of body clock misalignment, which the researchers say could be useful for assessing someone's risk of developing mood disorders in the future.
"This strong early evidence opens up exciting new ways we can study and potentially treat common mental health disorders and hopefully improve the lives the thousands of young Australians living with depression anxiety," says Dr Carpenter.
Research: Carpenter JS, et al. ' Evidence for Internal Misalignment of Circadian Rhythms in Youth With Emerging Mood Disorders ', Journal of Biological Rhythms, July 2025. DOI:10.1177/07487304251349408
Declaration: The research was approved by the University of Sydney Human Research Ethics Committee (02-2008/11445) and all participants gave written informed consent.
The research was partially supported by grants from the National Health & Medical Research Council (NHMRC) including an NHMRC Centre of Research Excellence (1061043), NHMRC Australia Fellowship (511921 awarded to Professor Hickie), NHMRC Emerging Leadership Fellowship (awarded to Dr Crouse), NHMRC Leadership Fellowship (2016346) and the Stephen Francis Bequest (awarded to Dr Carpenter).
Professor Ian Hickie is the Co-Director, Health and Policy at the Brain and Mind Centre (BMC) University of Sydney, Australia. The BMC operates an early-intervention youth services at Camperdown under contract to headspace. Professor Hickie has previously led community-based and pharmaceutical industry-supported (Wyeth, Eli Lily, Servier, Pfizer, AstraZeneca) projects focused on the identification and better management of anxiety and depression. He is the Chief Scientific Advisor to, and a 3.2 percent equity shareholder in, InnoWell Pty Ltd. InnoWell was formed as a joint venture by the University of Sydney (32 percent equity) and PwC (Australia; 32 percent equity) to deliver the $30m Australian Government-funded Project Synergy (2017-20; a three-year program for the transformation of mental health services) and to lead transformation of mental health services internationally through the use of innovative technologies. All other authors declare no conflict of interest.
Lead image credit: Licenced from Adobe Stock
