The gut microbiome and our digestive system is inextricably linked to human health and disease. Already we know there is a 2-way (bidirectional) communication pathway between the gut and different organs throughout the body including skeletal muscle, liver, bone and the brain. The gut-brain communication is carried out through the nervous system in particular the vagal nerve, as well as through hormonal and the immune system, all of which may be affected by the health of the gut microbiota. The importance of the microbiota-gut-brain axis is highlighted by studies linking dysbiosis or dysregulation of the gut microbiota to Parkinson’s disease, autism, increased anxiety and depression, decreased cognitive abilities as well as altered behavioural patterns and sleep.

Short sleep duration and poor sleep quality have also been associated with several aspects of cognitive and neurobehavioral performance, and several diseases including cancer, type II diabetes, and Alzheimer’s disease. Sleep also regulates mood, supports learning, and clears metabolic waste from the brain (hence one of the links with poor sleep and Alzheimer’s). 

Sleep has been shown to be intrinsically linked to the immune system and growing evidence suggests that the gut microbiota, which impacts our immune system, can influence our sleep quality. In addition, our sleep is regulated by our normal bodily processes and our circadian rhythm, which also appears to be related to the gut microbiome composition. Emerging studies have shown that the gut microbiota and its metabolites exhibit daily fluctuations and exhibit their own circadian rhythms, which predominantly respond to our eating habits. Our gut microbial metabolites influence our central and liver clock and sleep duration. They are all connected.

In support of this the research shows that metabolic disturbances associated with sleep loss may in fact be mediated through the overgrowth of specific gut bacteria and create a state of gut dysbiosis. Reciprocally, bacterial by-products from bacterial species which grow in response to sleep loss are able to induce fatigue. 

Studies on mice without any gut microbiota (germ-free) have been shown to have very different sleep patterns compared with conventionally-raised mice with normal gut microbiota. While, human patients with obstructive sleep apnea harbour lower quantities of bacteria which produce short-chain fatty acid (e.g., butyrate) derived from fermentation of dietary fibres. Moreover, in a study of just two nights of partial sleep deprivation in human subjects increased gut microbiome dysbiosis associated with metabolic risk.  While, in another study of 28 healthy young subjects, self-reported sleep quality was positively associated with gut microbial diversity as well as a positive association between sleep quality.1 Indicating that consuming the right types of butyrate producing fibre and prebiotics can improve sleep quality. 

In one study they found that microbiota diversity was positively correlated with increased sleep efficiency and total sleep time. The greater the microbial diversity in the gut the better the sleep. They also found a positive correlation between total microbiome diversity and the chemical messenger called interleukin-6, a cytokine previously noted for its effects on sleep2.

It appears that these chemical messengers, represent a potential critical link between sleep and our gut microbiome composition. The cytokines IL-1β (cytokine interleukin–1β) and IL-6 in particular, are strongly associated with sleep. IL-1β is a major factor which can induce sleep. In fact administration of IL-1β in human and other animals increases spontaneous sleep and fatigue. 

Collectively, these findings highlight a significant relationship between the gut microbiome and its metabolites with sleep. Furthermore, probiotic and prebiotic supplementation has been found to improve subjective sleep quality and visa-versa sleep quality and duration may be an important target for supporting healthy gut microbiota composition3. 

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References

1 Sleep Med. Author manuscript; available in PMC 2021 Sep 1. Sleep Med. 2020 Sep; 73: 76–81.  doi: 10.1016/j.sleep.2020.04.013 PMCID: PMC7487045 NIHMSID: NIHMS1587155 PMID: 32795890 Self-Reported Sleep Quality Is Associated With Gut Microbiome Composition in Young, Healthy Individuals: A Pilot Study Gregory J. Grosicki,1 Bryan L. Riemann,1 Andrew A. Flatt,1 Taylor Valentino,2 and Michael S. Lustgarten3

2 PLoS One. 2019; 14(10): e0222394. Published online 2019 Oct 7. doi: 10.1371/journal.pone.0222394 PMCID: PMC6779243 PMID: 31589627 Gut microbiome diversity is associated with sleep physiology in humans. Robert P. Smith, Cole Easson, et al 

3 Sleep Med Rev . 2020 Oct;53:101340. doi: 10.1016/j.smrv.2020.101340. Epub 2020 May 13. Sleep, circadian rhythm, and gut microbiota Brittany A Matenchuk  1 , Piush J Mandhane  1 , Anita L Kozyrskyj . PMID: 32668369 DOI: 10.1016/j.smrv.2020.101340