Eyes opened on the sleep-gut link


It’s well established that getting enough sleep is critical to ‘waking up on the right side of the bed’ and ensuring good mood and mental health and that lack of sleep can produce adverse mental health outcomes. Until recently, though, the link between the gut and sleep was insufficiently studied. New research that focuses on this relationship is now highlighting that many of us should be paying more attention to our gut microbiome and our sleep quality. 

Sleep and emotional well-being are intricately linked. When we don’t get enough sleep, we can be grumpy, moody and irritable. When people are chronically overtired or suffer from repeatedly disturbed sleep, they’re at an increased risk of mental health issues, such as depression, paranoia, anxiety and post-traumatic stress disorder.1<superscript> In reverse, those with mental health issues are more likely to experience sleep disruption and sleep disorders, such as insomnia.1

Mental health and sleep 

This link between mental health and sleep is well-researched, with robust evidence supporting that sleep is crucial to good mental and physical health. Findings suggest that the relationship between sleep and mental health is bidirectional, with poor mental health  associated with poorer sleep.2

Recent research from the University of Otago demonstrated that sleep quality is the biggest predictor of depressive symptoms among young adults. In a media release, lead author Shay-Ruby Wickham says sleep quality is stronger than sleep quantity as a predictor of mental health and well-being.

“This is surprising because sleep recommendations predominantly focus on quantity rather than quality,” she said. “While we did see that both too little sleep, or less than eight hours at a time, and too much sleep – more than 12 hours at a time – were associated with higher depressive symptoms and lower wellbeing, sleep quality significantly outranked sleep quantity in predicting mental health and wellbeing

“This suggests that sleep quality should be promoted alongside sleep quantity as a tool for improving mental health and wellbeing within young adults.”

Senior author Associate Professor Tamlin Conner, of the university’s Department of Psychology, says most previous research has examined these health behaviours in isolation from each other.

“We showed that they’re all important for predicting which young adults are flourishing versus suffering,” she said.

Associate Professor Conner stressed that the study’s findings were correlations only.

“We didn’t manipulate sleep, activity or diet to test their changes on mental health and wellbeing,” she said. “Other research has done that and has found positive benefits. Our research suggests that a ‘whole-health’ intervention prioritising sleep, exercise and fruit and vegetable intake together could be the next logical step in this research.”3

The Sleep Health Foundation’s tips for improving sleep include:

  • Having a set bedtime.
  • Winding down before bedtime.
  • Avoiding alcohol, tobacco and caffeine during the evening.
  • Dimming lights and avoiding electronic devices at least an hour before bedtime.
  • Avoiding daytime naps.
  • Exercising regularly and being exposed to natural light.2

The gut-sleep connection

The gut microbiome has been a research focus in recent years, specifically in studies involving the gut-brain axis – how the gut microbiota affects and interacts with brain function. The work has linked certain gut microbiome compositions to depressive symptoms and poor mental health.4

One way the brain and gut are linked is through the vagus nerve, which connects the intestine to the brain. Neurotoxic metabolites are produced by the gut microbiota and pass through the vagus nerve to the central nervous system, affecting brain function, stress and sleep structure.5

Studies suggest that the microbiota also exhibit circadian rhythms, and further research indicates that circadian rhythm disruption is linked to changes in sleep patterns. Disruption of the circadian rhythm also disrupts the gut microbiome equilibrium. In addition, depression and sleep are interconnected, with depressive symptoms among those affected often milder at night compared with the morning.5

Poor sleep quality affects gut health, and poor gut health affects sleep quality. Therefore, to improve sleep for mental health, perhaps we should look to improve the microbiome and implement healthy sleep habits.


  1. Sleep Health Foundation. ‘Mental health and Sleep’. 2021. org.au/mental-health-and-sleep-2.html [accessed 20/6/23].
  2. Sleep Health Foundation. ‘Ten tips for a good night’s sleep’. 2020. org.au/tips-for-a-good-night-s-sleep.html [accessed 21/6/23].
  3. University of Otago. ‘Sleep, food or exercise: which has the biggest impact on mental health?’ 2020. org/newsfeed/sleep,-food,-or-exercise-which-has-the-biggest-impact-on-mental-health [accessed 21/6/23].
  4. Springer Nature. ‘Gut bugs linked to depressive symptoms’. 2022. org/newsfeed/gut-bugs-linked-to-depressive-symptoms [accessed 20/6/23].
  5. Yuanyuan Li, et al. ‘The role of microbiome in insomnia, circadian disturbance and depression’. 2018. nlm.nih.gov/pmc/articles/PMC6290721/ [accessed 20/6/23].

This feature was originally published in the July issue of RPA e-magazine