Scientists know that circadian rhythms and the gut microbiome work together to impact health. The body’s internal clock (which regulates sleep, appetite, and other key physiological processes) and the flora in the GI tract help the body respond to environmental conditions. On a deeper level, though, researchers have yet to fully understand why and how they’re connected. Here are some insights into what is known when it comes to the links between the gut microbiome and circadian rhythms.
The gut microbiome changes throughout the day
Circadian clock genes regulate how the GI tract functions.1 It should come as no surprise, then, that the composition of gut flora oscillates depending on the time of day. As researchers discovered, the two main components of mammalian gut microbiota, Bacteroidetes and Firmicutes, change in quantity from day to night.2 During the active phase of the light: dark cycle, mammals have higher levels of bacteria, with lower levels during the inactive phase. Accordingly, one study found that mice harbor more bacteria (including more Bacteriodetes) at 11 p.m., and less bacteria (including more Firmicutes) at 7 a.m.3 Meanwhile, animals deprived of a light: dark cycle didn’t experience such shifts.
Stress affects the gut microbiome
Researchers are aware that several GI diseases are linked with the disruption of circadian rhythms and changes to the composition of the gut microbiome. Stress, including a shift in the sleep and wake or light: dark cycle, impacts the structure and diversity of gut flora in animals and humans.
Disruptions to circadian rhythms can reduce the total amount of healthful microorganisms and increase the populations of potentially harmful microorganisms that can lead to a lack of equilibrium in the gut. By way of evidence, one 2017 study assessed changes in microbiota composition after a military training exercise.4 Following four days of sleep restriction and other challenges, subjects’ gut flora changed in ways consistent with inflammation and a “leaky gut” (a harmful condition where more food particles, toxins, and bacteria penetrate the tissues beneath the gut lining). Similarly, mice exposed only to darkness for two weeks experienced no oscillations in the gut flora in their intestinal tract and an increase in the harmful bacteria, Clostridia, in their small intestines.
More stress has a larger impact
Disrupting circadian rhythms is challenging for lab animals and humans. However, adding another stressor at the same time (such as an unhealthy diet) truly poses a threat to the gut microbiome. As evidence of this, in a 2014 study, researchers disrupted the light: dark cycle of mice over several weeks.5 While they fed one group a standard healthy diet, they gave another a high-sugar, high-fat diet. The rats on the healthier diet experienced no change in their gut microbiota; however, the rats on the less healthy diet underwent significant changes, including more pro-inflammatory bacteria. Similarly, in a 2013 study, scientists showed that mice given alcohol and exposed to light: dark cycle disruptions experienced more gut leakiness (versus those not given alcohol).1
The takeaways
In general, try to reduce the stress on your body. Along with eating a healthful diet that’s full of nutrients and not high in fat, added sugar, or alcohol, prioritize your sleep. Go to bed at the same time each night and rise with the sun. Each morning, head outside to expose your body to sunlight and sync up with the light: dark cycle. Spend as much time as you can outside and avoid light within a couple of hours of bedtime. These simple strategies should make it easier for your body to function in an optimal state.
Resources:
1 Summa, K.C. et al. (2013). [Circadian rhythm disruption in mice increasing gut permeability]. PLoS One, PubMed Central
2 Liang, X et al. (2015). [Study on host circadian clock and thythmicity of gut microbiome]. Proceedings of the National Academy of Sciences of the United States of America, pnas.org
3 Gugliemi, G. (2020). [The gut microbiome and circadian rhythms influence on health]. Microbiomepost.com
4 Karl, J.P. et al (2017). [Study on stress, intestinal permeability and changes in microbiome composition]. American Journal of Physiological Gastrointestinal Liver Physiology, PubMed. gov
5Voigt, R.M. et al (2014). [Circadian rhythm disruption affects gut microbiome]. PLoS One, PubMed Central
Karl, J. P. et al (2018). [Study on environmental and physical stress on gut microbiome]. Fontiers in Microbiology, PubMed Central
Campos, M. (2021). [Report on leaky gut and what it means]. Harvard Health Publishing, health.harvard.edu
Li, Y. et al. (2018). [Gut microbiome, insomnia, circadian rhythms and depression]. Frontiers in Psychiatry, frontiersin.org
Voigt, R.M. et al. (2016). [Gut microbiome and circadian rhythms]. International Review of Neurobiology, PubMed.gov
Gutierrez Lopez, D.E. et al. (2021). [Review on circadian rhythms, gut microbiome and host metabolic response to diet]. Cell Metabolism, cell.com
