Nium.bio

The gut microbiota–sleep connection: mechanisms, evidence and open questions

Over the past decade, growing interest has emerged in the relationship between sleep and the gut microbiota. Evidence suggests that sleep habits, including duration, quality, and alignment with circadian rhythms, are associated with changes in gut microbial composition and function. In turn, gut microbes and the metabolites they produce may influence processes involved in sleep regulation. Experimental studies indicate that sleep loss and chronic sleep disruption can alter the microbiota and affect metabolic health, although findings have not been entirely consistent. At the same time, research has shown that the gut microbiota follows daily rhythms that are closely linked to feeding schedules and the host circadian system. While these observations point to a complex, bidirectional relationship, evidence in humans remains limited and sometimes conflicting.

Here, we review the existing literature on the sleep-microbiota relationship, highlighting evidence from human studies, circadian regulation, proposed biological pathways, and areas that warrant further investigation.

Introduction

Sleep is a fundamental biological process that supports metabolic health, immune function, cognitive performance, and overall physiological balance. Disrupted sleep, whether through insufficient sleep, insomnia, or misalignment of circadian rhythms, has been linked to a wide range of negative health outcomes. As a result, there is increasing interest in understanding the biological factors that connect sleep with health and disease. One area that has attracted growing attention is the gut microbiota, which plays an important role in metabolism, immune regulation, and communication between the gut and the central nervous system.

The relationship between sleep and the gut microbiota appears to be bidirectional. Sleep patterns and circadian rhythms can shape the intestinal environment by influencing feeding behaviour, hormone secretion, gastrointestinal function, and immune responses. At the same time, gut microbes produce a variety of metabolites and signalling molecules that may affect pathways involved in inflammation, metabolism, and brain function. However, the strength of evidence varies across these interactions. While daily oscillations in the gut microbiota driven by circadian rhythms are well established, direct causal effects of the microbiota on sleep in humans remain less clearly understood.

A systematic review covering 41 human studies published between 2016 and 2025 found that sleep duration, sleep disturbances, and circadian misalignment are associated with differences in gut microbial composition and function. However, results regarding microbial diversity were mixed, with no clear consensus across studies (Olson et al., 2026).

More recent meta-analyses have reported similar associations between sleep disturbances and changes in the gut microbiota, while also pointing out important limitations related to study quality and methodological heterogeneity (Chen et al., 2026; Wang et al., 2026). Together, these findings highlight the potential role of the gut microbiota in sleep-related physiology, but also emphasise the need for further research to clarify whether these relationships are causal.

Sleep disturbances and gut microbiota composition

Studies in humans have investigated the relationship between sleep characteristics and gut microbiota profiles, with several reporting differences in microbial composition between individuals with healthy and disrupted sleep. However, the lack of consistency across studies has limited the identification of specific microbial patterns that reliably characterise sleep disturbances.

In their review, Olson et al. (2026) found that sleep restriction, sleep disturbances, and circadian misalignment were linked to differences in gut microbial composition and function. However, results for alpha diversity, a measure of microbial diversity within a sample, were inconsistent across studies. The review also highlighted members of the Oscillospiraceae/Ruminococcaceae group as potentially associated with sleep and circadian parameters, although their specific role remains unclear and requires further investigation using higher-resolution taxonomic and functional analyses.

The relationship between insomnia and the gut microbiota has been explored in a systematic review and meta-analysis of 14 studies including 9,036 participants. Chen et al. (2026) reported differences in overall microbial community structure, as well as shifts in the relative abundance of several bacterial genera. Individuals with insomnia tended to show lower levels of Faecalibacterium and Lachnospira and higher levels of Blautia and Anaerobutyricum hallii. Many of these taxa have previously been linked to microbial fermentation, gut barrier function, and inflammatory processes.

Despite these observations, caution is warranted when interpreting individual taxonomic associations. Reported findings often differ between studies, likely reflecting variations in participant demographics, diet, medication use, sleep assessment methods, microbiome profiling techniques, and analytical approaches. In addition, relative abundance data provide limited information about absolute microbial abundance or functional activity. As a result, the biological significance of the reported microbial differences remains uncertain and will require confirmation in larger, longitudinal, and well-controlled human studies.

Experimental studies provide a complementary perspective because they can examine microbiome changes following controlled alterations in sleep.

Benedict et al. (2016) examined the effects of recurrent partial sleep deprivation in a small group of healthy, normal-weight young men. After two days of restricted sleep, participants showed alterations in specific bacterial taxa together with changes in glucose metabolism. Analysis of gut microbiota composition using V4 16S rRNA gene sequencing revealed an increased Bacillota:Bacteroidota ratio, higher relative abundances of the families Coriobacteriaceae and Erysipelotrichaceae, and a lower abundance of Mycoplasmatota, compared with periods of normal sleep. These microbial changes are of interest because similar patterns have previously been linked to metabolic disturbances in both animal and human studies. However, the effects were not observed consistently across all measures of microbial community structure, and the study did not establish a causal link between the microbiome alterations and the metabolic changes associated with sleep restriction.

In contrast, Zhang et al. (2017) found that experimental sleep restriction had only a limited impact on overall gut microbiome composition in both humans and rats. Although sleep restriction reduced operational taxonomic unit (OTU) richness in rats, the abundance of the major microbial groups remained largely unchanged. These findings challenge the notion that sleep loss consistently leads to marked microbiota disruption.

Taken together, these studies suggest that sleep restriction can be associated with changes in selected microbial features, but that such effects are not necessarily large, uniform or reproducible across experimental conditions. The evidence does not support the assumption that every episode of insufficient sleep produces a detectable change in gut microbiota composition (Benedict et al., 2016; Zhang et al., 2017).

Circadian rhythms as a link between sleep and the microbiota

Sleep is tightly linked to the circadian system, which orchestrates daily rhythms in physiology and behaviour. As a result, understanding the relationship between sleep and the gut microbiota requires consideration of not only sleep duration, but also sleep timing, feeding behaviour, and circadian alignment, all of which can influence the intestinal microbial ecosystem.

A landmark study by Thaiss et al. (2014) showed that the gut microbiota undergoes regular daily fluctuations in both composition and function. Using experimental models and human data, the authors demonstrated that these microbial rhythms are shaped by feeding patterns and can be disrupted by circadian misalignment. They further observed that transferring microbiota from animals with disrupted circadian rhythms to germ-free mice contributed to metabolic disturbances in the recipients. While the study did not examine sleep directly, it provided important evidence that circadian rhythms influence microbial activity and that alterations in these rhythms can have functional consequences for host metabolism. These findings helped establish a mechanistic framework linking circadian regulation, the gut microbiota, and metabolic health.

Subsequent studies showed that microbial daily rhythms involve more than shifts in community composition alone. Thaiss et al. (2016) demonstrated that the location of microbes within the intestine, as well as their metabolic activity, changes over the course of the day. These fluctuations were linked to daily patterns in host gene expression, epigenetic regulation, and metabolism, suggesting that microbiota function varies according to time of day and may contribute to the temporal organisation of host physiology.

These findings have important implications for sleep research. People exposed to shift work, irregular sleep schedules, or circadian misalignment often experience disrupted eating patterns and altered daily behaviours. Such changes may affect when and how the gut microbiota functions, even in the absence of major changes in overall microbial diversity. As a result, growing attention has been directed towards the circadian microbiome as a potential mediator of the health effects associated with irregular sleep schedules (Litichevskiy & Thaiss, 2022; Thaiss et al., 2014, 2016).

It is important, however, to distinguish between circadian disruption and sleep deprivation. Circadian misalignment occurs when internal biological rhythms are out of sync with behavioural or environmental cues, whereas sleep deprivation simply reflects an insufficient amount of sleep. Although these conditions often occur together, they are not interchangeable and may affect physiology through different mechanisms. Future studies that clearly separate the effects of sleep loss from those of circadian misalignment will be essential for understanding their respective contributions to changes in the gut microbiota and host health.

Potential mechanisms linking gut microbiota and sleep

Several biological pathways could mediate interactions between the gut microbiota and sleep. These mechanisms are biologically plausible and supported to varying degrees by microbiome, circadian and host-physiology research. However, direct evidence that they mediate sleep outcomes in humans remains limited.

The gut microbiota generates a wide range of metabolites through the fermentation of dietary components and the modification of host-derived compounds. Among these, short-chain fatty acids (SCFAs), such as acetate, propionate, and butyrate, have attracted particular interest because of their roles in maintaining intestinal barrier integrity, regulating immune responses, and supporting metabolic signalling.

Given these functions, alterations in microbial composition or activity may affect pathways that are relevant to sleep, including inflammation, metabolic regulation, and gut-brain communication. In addition, evidence that microbial metabolite production follows daily rhythms suggests that both the quantity and timing of host exposure to these compounds may be influenced by circadian processes (Thaiss et al., 2016).

Despite these observations, the contribution of SCFAs to sleep regulation remains poorly understood. It is not yet clear whether specific SCFAs directly influence sleep in humans, whether any effects depend on their concentration or timing of production, or whether they help explain the associations observed between the gut microbiota and sleep disorders such as insomnia. Addressing these questions will require studies that combine microbiome sequencing with metabolomic analyses and objective assessments of sleep.

The gut-brain axis refers to the network of communication between the gastrointestinal tract and the central nervous system, involving neural, endocrine, immune, and metabolic pathways. Through the production of metabolites and other signalling molecules, the gut microbiota can influence these pathways by interacting with intestinal cells, modulating immune responses, and affecting host signalling processes.

This concept provides a biological basis for a potential link between microbial activity in the gut and sleep-related physiology. The relationship may also operate in the opposite direction, as sleep disturbances can alter stress responses, autonomic nervous system activity, and gastrointestinal function, all of which may affect gut microbial communities. However, the existence of these communication pathways does not necessarily mean that microbiota-related changes have a measurable or clinically relevant impact on sleep in humans.

It is also unlikely that the relationship can be explained by the presence or absence of a single bacterial taxon or metabolite. Instead, any effects are likely to emerge from complex interactions between microbial functions, host physiology, diet, lifestyle, and environmental factors. For this reason, future research should focus on functional and mechanistic approaches that can test causality, rather than relying solely on comparisons of microbial composition (Litichevskiy & Thaiss, 2022; Olson et al., 2026).

Methodological limitations and future directions

Although interest in the links between sleep and the gut microbiota has increased rapidly in recent years, several challenges continue to limit the strength of current conclusions.

One major issue is the lack of methodological consistency across studies. Researchers use different definitions of sleep disturbances, rely on either subjective or objective measures of sleep, and vary in the duration of sleep interventions and the timing of sample collection. As a result, studies addressing similar questions do not always produce comparable results.

Another challenge is the large number of factors that can influence both sleep and the gut microbiota. Diet, medications, age, physical activity, stress, and metabolic health are all known to affect microbial communities and sleep patterns. In populations such as shift workers, additional factors including altered meal timing and light exposure further complicate interpretation, making it difficult to isolate the specific contribution of sleep-related variables.

A further limitation is that changes in microbial composition do not necessarily reflect changes in microbial activity. Taxonomic analyses can identify which microorganisms are present, but provide only limited information about their functional roles, metabolic outputs, or interactions with the host. Because microbial activity also fluctuates throughout the day, single time-point measurements are unlikely to capture the full picture. Integrating repeated sampling with approaches such as metagenomics and metabolomics may provide a more detailed understanding of these dynamic processes.

Establishing causality remains perhaps the greatest challenge. Most human studies are observational and cannot determine whether alterations in the microbiota contribute to sleep disturbances or arise as a consequence of them. Experimental studies involving sleep manipulation have provided valuable insights, but their findings have not always been consistent. Animal models and microbiota-transfer experiments can help explore potential mechanisms, although their relevance to human sleep physiology must be interpreted with caution.

Conclusion

The evidence available to date suggests that sleep and the gut microbiota are linked through a complex interplay of behavioural, circadian, metabolic, and physiological factors. Human studies have reported associations between sleep disturbances and differences in gut microbial communities, while experimental work indicates that sleep loss and circadian disruption can affect both microbial and host responses. In particular, research on daily microbial rhythms has highlighted the importance of timing, suggesting that sleep and feeding schedules may shape not only the composition of the gut microbiota but also its activity and interactions with the host.

Despite these advances, many questions remain unanswered. Current findings do not support the existence of a consistent microbiome profile associated with poor sleep or insomnia, and it is still unclear whether observed microbial changes contribute to sleep disturbances or simply reflect them. Future studies should focus on capturing both microbial composition and function over time, while incorporating objective measures of sleep and circadian rhythms. Such approaches will be critical for disentangling cause-and-effect relationships and determining whether the gut microbiota could become a meaningful target for strategies aimed at improving sleep health.

References

Benedict, C., Vogel, H., Jonas, W., Woting, A., Blaut, M., Schürmann, A., & Cedernaes, J. (2016). Gut microbiota and glucometabolic alterations in response to recurrent partial sleep deprivation in normal-weight young individuals. Molecular metabolism, 5(12), 1175–1186. https://doi.org/10.1016/j.molmet.2016.10.003

Chen, S., Li, H., Ning, M., Yu, B. Y. M., Wu, S., Cheng, W. Y., Li, Y., & Yeung, W. F. (2026). The association between gut microbiota and insomnia: A systematic review and meta-analysis. Sleep medicine reviews, 86, 102236. https://doi.org/10.1016/j.smrv.2026.102236

Litichevskiy, L., & Thaiss, C. A. (2022). The Oscillating Gut Microbiome and Its Effects on Host Circadian Biology. Annual review of nutrition, 42, 145–164. https://doi.org/10.1146/annurev-nutr-062320-111321

Olson, M., Withrow, D., Koelbel, M., Southworth, G., Phan, A., Wright, K. P., Jr, Whisner, C. M., & Petrov, M. E. (2026). What is the nature of sleep and circadian rhythm health on gastrointestinal microbiota? A systematic review of studies in humans. Sleep medicine reviews, 86, 102256. https://doi.org/10.1016/j.smrv.2026.102256

Thaiss, C. A., Zeevi, D., Levy, M., Zilberman-Schapira, G., Suez, J., Tengeler, A. C., Abramson, L., Katz, M. N., Korem, T., Zmora, N., Kuperman, Y., Biton, I., Gilad, S., Harmelin, A., Shapiro, H., Halpern, Z., Segal, E., & Elinav, E. (2014). Transkingdom control of microbiota diurnal oscillations promotes metabolic homeostasis. Cell, 159(3), 514–529. https://doi.org/10.1016/j.cell.2014.09.048

Thaiss, C. A., Levy, M., Korem, T., Dohnalová, L., Shapiro, H., Jaitin, D. A., David, E., Winter, D. R., Gury-BenAri, M., Tatirovsky, E., Tuganbaev, T., Federici, S., Zmora, N., Zeevi, D., Dori-Bachash, M., Pevsner-Fischer, M., Kartvelishvily, E., Brandis, A., Harmelin, A., Shibolet, O., … Elinav, E. (2016). Microbiota Diurnal Rhythmicity Programs Host Transcriptome Oscillations. Cell, 167(6), 1495–1510.e12. https://doi.org/10.1016/j.cell.2016.11.003

Wang, Z., Wu, T., Li, J., Dong, G., Kong, L., Zhang, Y., Zhang, Z., Lv, Z., Zhang, Y., Zhan, R., Li, R., Shan, Y., Zhang, C., Wang, Z., Chen, S., Vitiello, M. V., Wing, Y. K., Wang, Y., Zheng, Y., Bao, Y., … Lu, L. (2026). Gut microbiota alterations in sleep disturbances: A systematic review and meta-analysis. Sleep medicine reviews, 88, 102293. https://doi.org/10.1016/j.smrv.2026.102293

Zhang, S. L., Bai, L., Goel, N., Bailey, A., Jang, C. J., Bushman, F. D., Meerlo, P., Dinges, D. F., & Sehgal, A. (2017). Human and rat gut microbiome composition is maintained following sleep restriction. Proceedings of the National Academy of Sciences of the United States of America, 114(8), E1564–E1571. https://doi.org/10.1073/pnas.1620673114